Patent Publication Number: US-2021169941-A1

Title: Multistrain population control systems and methods

Description:
CLAIM OF PRIORITY 
     This application claims the benefit of U.S. Provisional patent Application Ser. No. 62/682,755, filed Jun. 8, 2018, the entire contents of which are hereby incorporated by reference. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under Grant Nos. RO1-GM069811 awarded by the National Institutes of Health and National Institute of General Medical Sciences. The Government has certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to methods, systems, kits, and compositions for culturing bacterial cells, and more particularly to methods, systems, kits, and compositions for multi-strain ecosystems, including a quorum-regulated multi-lysis system. 
     BACKGROUND 
     Microbial ecologists are increasingly turning to small, synthesized ecosystems 1-5  as a reductionist tool to probe the complexity of native microbiomes 6, 7 . Concurrently, synthetic biologists have gone from single-cell gene circuits 8-11  to controlling whole populations using intercellular signaling 12-16 . 
     SUMMARY 
     Without wishing to be bound by theory, the present inventors disclose a tri-lysis or multi-lysis system that can be used to engineer multi-strain ecosystems and/or enable cyclical delivery of one or more payloads, such as therapeutic agents. Each strain can deliver, e.g., a payload of a single therapeutic protein or multiple therapeutic proteins, while excluding previously administered strains, or previously existing strains, in the site of disease. For example, there may be at least three strains that comprise this system, wherein each strain produces a toxin, which kills one of the other two strains, and an antitoxin to protect itself, and the other strains not targeted by the toxin. For example, in an exemplary system comprising strains labeled strain A, strain B, and strain C, strain A can produce a toxin that kills strain B; strain B, in turn, can produce a toxin that kills strain C, and strain C can produce a toxin that kills strain A. More strains can be present in the system, and may or may not participate in the cyclical toxin system. The system is not limited to a three strain system, it can potentially be composed of more than three strains (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 strains), where each strain produces a toxin with the ability to kill another strain in the system which does not have the anti-toxin, thereby allowing a cyclical system (composed of four, five, six, seven, eight, nine, ten, eleven, twelve or more strains). Additionally, it is possible that the system is composed of more than three strains (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 strains), wherein each of at least three of the strains produces a toxin with the ability to kill another strain in the system which does not have the anti-toxin, thereby allowing a cyclical system among at least three of the strains while other strains of the system are not controlled according to the tri-lysis or multi-lysis circuit. In one aspect, such a system can provide specific delivery of a therapeutic agent(s) via engineered strains for a certain amount of time until a subsequent strain in the system is administered, thereby separating the delivery of certain therapeutic agent(s) in space and time, as desired. 
     In some embodiments, each of the strains can produce a therapeutic protein or a suite of therapeutic proteins, the expression of which can be controlled by a genetic circuit such as a Synchronized Lysis Circuit (SLC). In some embodiments, exemplary SLC&#39;s can include those described in International Application No. PCT/US18/33555, which is incorporated herein by reference in its entirety. 
     In some embodiments, a tri-lysis or multi-lysis system utilizes a well characterized  E. coli  specific toxin-antitoxin system, combined with a Lux AHL quorum sensing lysis circuit, to not only provide self-limiting control of bacterial population size, but also enable the precise removal of unwanted strains in a cyclic “rock paper scissors” fashion that enables long term continuous culture. A tri-lysis or multi-lysis system ensures specific delivery of a therapeutic protein(s) via engineered strains for a certain amount of time until a subsequent strain in the system is administered, thereby separating the delivery of certain therapeutic protein(s) in space and time. A tri-lysis or multi-lysis system may also be engineered to output specific profiles of therapeutic proteins to the disease site. 
     In another aspect, the tri-lysis or multi-lysis system can also be applicable to engineering ‘division of labor’ ecosystems where multiple strains may metabolize or produce certain intermediates with the goal of synthesizing a commercially valuable compound. Additional similar applications the tri-lysis or multi-lysis system can include remediation and sensing applications. 
     Additionally, the use of the tri-lysis or multi-lysis system as a method to ensure circuit stability is not necessarily limited to therapeutic applications, it may be applicable to any application where the stability of engineered genetic constructs in bacteria are necessary. 
     Provided herein are methods of maintaining a co-culture by quorum sensing that include: co-culturing at least three (e.g., 3, 4, 5, 6, 7, 8, 9, 10) bacterial strains at certain ratios (e.g., 1:1:1) during a period of time; wherein each of the at least three bacterial strains comprises a lysis plasmid and an activator plasmid. 
     Also provided herein are methods of maintaining a co-culture by quorum sensing that include: co-culturing at least three (e.g., 3, 4, 5, 6, 7, 8, 9, 10) bacterial strains at certain ratios (e.g., 1:1:1) during a period of time; wherein each of the at least three bacterial strains comprises a toxin system. 
     Also provided herein are methods of maintaining a co-culture that include: co-culturing at least three (e.g., 3, 4, 5, 6, 7, 8, 9, 10) bacterial strains at certain ratios (e.g., 1:1:1) during a period of time; wherein each of the at least three bacterial strains comprises a toxin system. 
     In some embodiments, the at least three bacterial strains are  E. coli, S. typhimurium , or a bacterial variant thereof. In some embodiments, the at least three bacterial strains are Gram-negative bacterial strains, e.g., a  Salmonella  strain, an  Acetobacter  strain, an  Enterobacter  strain, a  Fusobacterium  strain, a  Helicobacter  strain, a  Klebsiella  strain, or an  E. coli  strain. In some embodiments, the at least three bacterial strains are Gram-positive bacterial strains, e.g., a  Actinomyces  strain, a  Bacillus  strain, a  Clostridium  strain, an  Enterococcus  strain, or a  Lactobacillus  strain. In some embodiments, the at least three bacterial strains are all Gram negative bacterial strains or all Gram positive strains. In some embodiments, at least one of the at least three bacterial strains is a Gram negative bacterial strain. In some embodiments, at least one of the at least three bacterial strains is a Gram positive bacterial strain. 
     In some embodiments, the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, a degradation tag, and optionally a reporter gene. In some embodiments, the lysis gene is E from a bacteriophage ΦX174. In some embodiments, the activatable promoter is a LuxR-N-acyl homoserine lactone (AHL) activatable luxI promoter and the activator gene is a LuxI. In some embodiments, the activatable promoter is a RpaR-N-acyl homoserine lactone (AHL) activatable RpaI promoter and the activator gene is a RpaI. In some embodiments, the reporter gene is green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP) or a variant thereof. In some embodiments, the degradation tag is an ssrA-LAA degradation tag. In some embodiments, each of the at least three bacterial stains comprises the lysis plasmid and the activator plasmid. In some embodiments, each of the at least three bacterial strains comprises a different reporter gene. 
     In some embodiments, the co-culture is inoculated at a ratio of 1:1:1. In some embodiments one or more bacterial strains can be co-cultured. In some embodiments, the co-culture is inoculated at certain ratios (e.g., 1:1, 1:5, 1:10, 1:1:1, 1:5:1, and the like) based on the strains used, the desired characteristics of the system, the outcome goals, and the like. In some embodiments, one or more strain in a system may have a growth advantage over one or more other strains in the system. 
     In some embodiments, the plasmid is integrated into a genome of the at least one of the at least three bacterial strains. 
     In some embodiments, the co-culturing occurs in a microfluidic device. In some embodiments, the co-culturing occurs in a cell culture vessel (e.g., a cell culture plate, a bioreactor). 
     In some embodiments, the period of time is 0 to 72 hours (e.g., 0 to 72; 0 to 60 hours; 0 to 48 hours; 0 to 36 hours; 0 to 24 hours; 0 to 16 hours; 0 to 14 hours; 0 to 12 hours; 0 to 10 hours; 0 to 8 hours; 0 to 6 hours; 0 to 4 hours; 0 to 2 hours; 2 to 72 hours; 2 to 60 hours; 2 to 48 hours; 2 to 36 hours; 2 to 24 hours; 2 to 16 hours; 2 to 14 hours; 2 to 12 hours; 2 to 10 hours; 2 to 8 hours; 2 to 6 hours; 2 to 4 hours; 4 to 72 hours; 4 to 60 hours; 4 to 48 hours; 4 to 36 hours; 4 to 24 hours; 4 to 16 hours; 4 to 14 hours; 4 to 12 hours; 4 to 10 hours; 4 to 8 hours; 4 to 6 hours; 6 to 8 hours; 6 to 10 hours; 6 to 12 hours; 6 to 14 hours; 6 to 16 hours; 6 to 18 hours; 6 to 20 hours; 6 to 22 hours 6 to 24 hours; 8 to 10 hours; 8 to 12 hours; 8 to 16 hours; 8 to 24 hours; 8 to 36 hours; 8 to 48 hours; 8 to 60 hours; 8 to 72 hours; 1 to 2 hours; 1 to 3 hours; 1 to 4 hours; 1 to 6 hours; 1 to 8 hours; 1 to 10 hours; 1 to 12 hours; 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 or 72 hours). 
     In some embodiments, the co-culturing of the at least three bacterial strains is in a constant lysis state; wherein the constant lysis state is characterized by a steady-state balance of growth and lysis of the at least three bacterial strains. 
     Provided herein are bacterial strains including a lysis plasmid and an activator plasmid; wherein the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, a degradation tag, and optionally a reporter gene. 
     In some embodiments, the lysis gene is E from a bacteriophage ΦX174. 
     In some embodiments, the activatable promoter is a LuxR-N-acyl homoserine lactone (AHL) activatable luxI promoter and the activator gene is a LuxI. 
     Also provided herein are pharmaceutical composition that include any of the bacterial strains described herein. In some embodiments, the pharmaceutical composition is formulated for in situ drug delivery. A pharmaceutical composition is formulated to be compatible with its intended route of administration. Examples of routes of administration include oral or parenteral, e.g., intravenous, intradermal, subcutaneous, inhalation, transdermal (topical), transmucosal, and rectal administration. As used herein the language “pharmaceutically acceptable carrier” includes solvents, dispersion media, coatings, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. Supplementary active compounds can also be incorporated into the compositions. 
     Provided herein are systems including: a co-culture of at least three bacterial strains as described herein. 
     Provided herein are drug delivery systems including any of the systems described herein. Provided herein are periodic drug delivery systems including any of the systems described herein. 
     Provided herein are methods for treating a disease in a subject, comprising: administering to a subject in need therapeutically effective amounts of at least three bacterial strains as described herein, or a pharmaceutical composition as described herein, to treat the disease in the subject. In some embodiments, the administering comprises administering sequentially each of the at least three bacterial strains to the subject. In some embodiments, the administering comprises administering each of the at least three bacterial strains simultaneously. In some embodiments, each of the at least three bacterial strains expresses a different therapeutic agent. In some embodiments, the disease is cancer or an infection. 
     Provided herein are microfluidic sample traps including any of the systems described herein. 
     Provided herein are microfluidic devices including one or more microfluidic sample traps. In some embodiments, the microfluidic system further includes at least one channel in fluid communication with the microfluidic sample trap. 
     Provided herein is a method including culturing a first bacterial strain for a first period of time in a growth environment, adding a second bacterial strain to the growth environment and culturing the second bacterial strain for a second period of time, adding a third bacterial strain to the growth environment and culturing the third bacterial strain for a third period of time, wherein each of the first, second, and third bacterial strains includes a toxin system, wherein the toxin system of the first bacterial strain produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the toxin system of the second bacterial strain produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, and wherein the toxin system of the third bacterial strain produces a third toxin/third antitoxin pair and the second antitoxin from the second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, and optionally wherein each of the first, second, and third bacterial strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum-sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum-sensing molecule. 
     Implementations can include one or more of the following features. The quorum-sensing molecule can be different in each of the first, second, and third bacterial strains. Each quorum-sensing molecule of each of the first, second, and third bacterial strains can have no or substantially no effect on the activatable promoter of the lysis gene of another strain. The quorum-sensing molecule can be the same in each of the first, second, and third bacterial strains. The method can further include culturing or co-culturing one or more additional bacterial strains in the growth environment. Each of the one or more additional bacterial strains can include a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum-sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum-sensing molecule. The quorum-sensing molecule can be different in each of the first, second, third, and one or more additional bacterial strains. Each quorum-sensing molecule of each of the first, second, third, and one or more additional bacterial strains can have no or substantially no effect on the activatable promoter of the lysis gene of another bacterial strain used in the growth environment. The quorum sensing molecule can be the same in each of the first, second, third, and one or more additional bacterial strains. Each of the one or more additional bacterial strains can include a toxin system. The toxin system of the first bacterial strain, the second bacterial strain, the third bacterial strain, and each of the one or more additional bacterial strains can be independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. The lysis plasmid and activator plasmid of each of the at least first, second, and third bacterial strains can be copies of the same plasmid. The lysis plasmid and activator plasmid of each of the at least the first, second, and third bacterial strains can be different plasmids. At least the first, second, and third bacterial strains can be metabolically competitive. At least the first, second, and third bacterial strains can be selected from  E. coli, S. typhimurium , or a bacterial variant thereof. Each of the at least the first, second, and third bacterial strains can not have a growth advantage compared to another strain in the growth environment. In each of the at least the first, second, and third bacterial strains, the lysis plasmid can include a lysis gene, an activatable promoter, and optionally a reporter gene, and the activator plasmid includes an activator gene, optionally a degradation tag, and optionally a reporter gene. The lysis gene in each of the at least the first, second, and third bacterial strains can be E from a bacteriophage ΦX174. The activatable promoter in each of the at least the first, second, and third bacterial strains can be a LuxR-AHL activatable luxI promoter and the activator gene can be a LuxI. At least one reporter gene can be selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof. The degradation tag can be an ssrA-LAA degradation tag. At least one of the plasmids can be integrated into a genome of at least one of the first, second, and third bacterial strains. The culturing can occur in a microfluidic device. The culturing can occur in a bioreactor. The culturing can occur in vivo. Each of the first, second, and third periods of time can range from about 12 to about 72 hours. Each of the first, second, and third periods of time can be selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours. Each of the first, second, and third periods of time can be selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 72 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 48 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 24 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 18 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 12 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 6 hours. Each of the first, second, and third periods of time independently can range from about 1 hours to about 3 hours. The first, second, and third periods of time can occur sequentially. The first and second, second and third, or first and third periods of time can partially or completely overlap. One or more of the first, second, and third bacterial strains can encode a heterologous nucleic acid and/or a heterologous protein operably linked to a promoter. The promoter can be an activatable promoter. The promoter can be activated by the quorum sensing molecule. The promoter can be a constitutive promoter. The heterologous nucleic acid and/or heterologous protein can be a therapeutic agent. The therapeutic agent can be selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof. The inhibitory nucleic acid can be siRNA, shRNA, miRNA, or antisense. 
     Also provided herein is a method including providing n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, co-culturing each of the bacterial strains sequentially for an independent period of time in a growth environment, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein each of the n bacterial strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Implementations can include one or more of the following features. In each of the n bacterial strains, the lysis plasmid can include a lysis gene, an activatable promoter, and optionally a reporter gene, and the activator plasmid includes an activator gene, optionally a degradation tag, and optionally a reporter gene. The lysis gene in each of the n bacterial strains can be E from a bacteriophage ΦX174. The activatable promoter in each of the n bacterial strains can be a LuxR-AHL activatable luxI promoter and the activator gene can be a LuxI. At least one reporter gene can be selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof. The degradation tag can be an ssrA-LAA degradation tag. At least one of the plasmids can be integrated into a genome of at least one of the n bacterial strains. The quorum-sensing molecule can be different in each of the n bacterial strains. Each quorum-sensing molecule of each of then bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another strain. The quorum-sensing molecule can be the same in each of then bacterial strains. The lysis plasmid and activator plasmid of each of the n bacterial strains can be copies of the same plasmid. The lysis plasmid and activator plasmid of each of the n bacterial strains are different plasmids. 
     Also provided herein is a method including providing n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, co-culturing each of the bacterial strains sequentially for an independent period of time in a growth environment, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n bacterial strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. The n bacterial strains can be metabolically competitive. Each of the n bacterial strains can be selected from  E. coli, S. typhimurium , or a bacterial variant thereof. Each of the n bacterial strains can not have a growth advantage compared to another strain in the growth environment. The toxin system of the n bacterial strains can be independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. The culturing can occur in a microfluidic device. The culturing can occur in a bioreactor. The culturing can occur in vivo. Each of the independent periods of time can range from about 12 to about 72 hours. Each of the independent periods of time can be selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours. Each of the independent periods of time can be selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours. Each of the periods of time independently can range from about 1 hours to about 72 hours. Each of the periods of time independently can range from about 1 hours to about 48 hours. Each of the periods of time independently can range from about 1 hours to about 24 hours. Each of the periods of time independently can range from about 1 hours to about 18 hours. Each of the periods of time independently can range from about 1 hours to about 12 hours. Each of the periods of time independently can range from about 1 hours to about 6 hours. Each of the periods of time independently can range from about 1 hours to about 3 hours. One or more of the periods of time can partially or completely overlap. One or more of the n bacterial strains can encode a heterologous nucleic acid and/or a heterologous protein operably linked to a promoter. The promoter can be an activatable promoter. The activatable promoter can be activated by a quorum-sensing molecule. The promoter can be a constitutive promoter. The heterologous nucleic acid and/or heterologous protein can be a therapeutic agent. The therapeutic agent can be selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof. The inhibitory nucleic acid can be siRNA, shRNA, miRNA, or antisense. Each of the second bacterial strain through the nth bacterial strain can not produce the second toxin of the toxin system of the previous strain, and the first bacterial strain can not produce the fourth toxin of the toxin system of the nth bacterial strain. 
     Also provided herein is a bacterial strain including a lysis plasmid and an activator plasmid, wherein the lysis plasmid includes a lysis gene, an activatable promoter, and optionally a reporter gene, and the activator plasmid includes an activator gene, optionally a degradation tag, and optionally a reporter gene, wherein the bacterial strain further includes a toxin system, wherein the toxin system produces a first toxin/first antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the bacterial strain does not produce the second toxin. 
     Implementations can include one or more of the following features. The lysis gene can be E from a bacteriophage ΦX174. The activatable promoter can be a LuxR-AHL activatable luxI promoter and the activator gene can be a LuxI. The activator gene can encode a molecule that activates, directly or indirectly, the activatable promoter. The molecule that activates, directly or indirectly, the activatable promoter can be a quorum-sensing molecule. The lysis gene can be operably linked to the activatable promoter. The reporter gene on the lysis plasmid can be operably linked to the activatable promoter. The activator plasmid can further include an activatable promoter. The activatable promoter of the activator plasmid can be a copy of the activatable promoter of the lysis plasmid. The activator gene can be operably linked to the activatable promoter of the activator plasmid. The reporter gene of the activator plasmid can be operably linked to the activatable promoter of the activator plasmid. The degradation tag can be operably linked to the activatable promoter of the activator plasmid. The toxin system can be operably linked to the activatable promoter of the lysis plasmid. The degradation tag can be an ssrA-LAA degradation tag. The reporter gene of the lysis plasmid, the reporter gene of the activator plasmid, or both, can be fluorescent proteins. The reporter gene of the lysis plasmid and the reporter gene of the activator plasmid can be different genes. 
     Also provided herein is bacterial strain including a toxin system, wherein the toxin system produces a first toxin/first antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the bacterial strain does not produce the second toxin. 
     Implementations can include one or more of the following features. The bacterial strain can encode a heterologous nucleic acid and/or a heterologous protein operably linked to a promoter. The promoter can be an activatable promoter. The activatable promoter can be activated by a quorum-sensing molecule. The promoter can be a constitutive promoter. The heterologous nucleic acid and/or heterologous protein can be a therapeutic agent. The toxin system can be encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. The bacterial strain can further include a nucleic acid encoding a therapeutic agent. The therapeutic agent can be selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof. The therapeutic agent can be a therapeutic polypeptide. The therapeutic agent can be cytotoxic or cytostatic to a target cell. The target cell can be a cancer cell or an infected cell. 
     Also provided herein is a pharmaceutical composition including any one or more of the bacterial strains described herein. The pharmaceutical composition can be formulated for in situ drug delivery. 
     Also provided herein is a system including a first bacterial strain including a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, wherein the first bacterial strain further includes a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, a second bacterial strain including a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, optionally a second degradation tag, and optionally a second reporter gene, wherein the second bacterial strain further includes a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, and a third bacterial strain including a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene, wherein the third bacterial strain further includes a third toxin system, wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Also provided herein is a system including first bacterial strain including a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further includes a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, a second bacterial strain including a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further includes a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, optionally a second degradation tag, and optionally a second reporter gene, and a third bacterial strain including a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further includes a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Implementations of some systems can include one or more of the following features. The system can further include one or more additional bacterial strains. The first toxin system, the second toxin system, and the third toxin system can be independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. 
     Also provided herein is a system including n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Also provided herein is a system including n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an n th  bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein each of the n bacterial strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Implementations of some systems can include one or more of the following features. The value of n can be 3. The value of n can be 4, 5, 6, 7, 8, 9, or 10. Each of the toxin systems can be independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. Each of the second bacterial strain through the nth bacterial strain can not produce the second toxin of the toxin system of the previous strain, and the first bacterial strain does not produce the fourth toxin of the toxin system of the nth bacterial strain. 
     Also provided herein is a kit including a first pharmaceutical composition including a first bacterial strain including a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, a first degradation tag, and optionally a first reporter gene, wherein the first bacterial strain further includes a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, a second pharmaceutical composition including a second bacterial strain including a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, a second degradation tag, and optionally a second reporter gene, wherein the second bacterial strain further includes a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, and a third pharmaceutical composition including a third bacterial strain including a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, a third degradation tag, and optionally a third reporter gene, wherein the third bacterial strain further includes a third toxin system, wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Also provided here is a kit including a first pharmaceutical composition including a first bacterial strain including a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further includes a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, a second pharmaceutical composition including second bacterial strain including a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further includes a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, optionally a second degradation tag, and optionally a second reporter gene, and a third pharmaceutical composition including a third bacterial strain including a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further includes a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Implementations of some kits can include one or more of the following features. The first toxin system, the second toxin system, and the third toxin system can independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. The kit can further include one or more additional bacterial strains in the first, second, third, and/or one or more additional pharmaceutical compositions. 
     Also provided herein is a kit including n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Also provided herein is a kit including n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the lysis plasmid of each of the n bacterial strains includes a toxin system, wherein the toxin system of the lysis plasmid of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the lysis plasmid of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the n th  bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Implementations of some kits can include one or more of the following features. The value of n can be 3. The value of n can be 4, 5, 6, 7, 8, 9, or 10. 
     Also provided herein is a drug delivery system including any one or more of the systems or kits provided herein. 
     Also provided herein is a periodic drug delivery system including any one or more of the systems or kits provided herein. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of a first bacterial strain including a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, wherein the first bacterial strain further includes a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, a second bacterial strain including a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, optionally a second degradation tag, and optionally a second reporter gene, wherein the second bacterial strain further includes a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, and a third bacterial strain including a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene, wherein the third bacterial strain further includes a third toxin system, wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of: a first pharmaceutical including a first bacterial strain including a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, wherein the first bacterial strain further includes a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, a second pharmaceutical including a second bacterial strain including a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, optionally a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, a second degradation tag, and optionally a second reporter gene, wherein the second bacterial strain further includes a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, and a third pharmaceutical including a third bacterial strain including a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene, wherein the third bacterial strain further includes a third toxin system, wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of: a first bacterial strain including a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further includes a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, a second bacterial strain including a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further includes a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, optionally a second degradation tag, and optionally a second reporter gene, and a third bacterial strain including a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further includes a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of: a first pharmaceutical composition including a first bacterial strain including a first toxin system, wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further includes a first lysis plasmid and a first activator plasmid, wherein the first lysis plasmid includes a first lysis gene, a first activatable promoter, and optionally a first reporter gene, and the first activator plasmid includes a first activator gene, optionally a first degradation tag, and optionally a first reporter gene, a second pharmaceutical composition including second bacterial strain including a second toxin system, wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further includes a second lysis plasmid and a second activator plasmid, wherein the second lysis plasmid includes a second lysis gene, a second activatable promoter, and optionally a second reporter gene, and the second activator plasmid includes a second activator gene, optionally a second degradation tag, and optionally a second reporter gene, and a third pharmaceutical composition including a third bacterial strain including a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further includes a third lysis plasmid and a third activator plasmid, wherein the third lysis plasmid includes a third lysis gene, a third activatable promoter, and optionally a third reporter gene, and the third activator plasmid includes a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Implementations of some methods can include one or more of the following features. Administering can include administering sequentially each of the first, second, and third bacterial strains or first second and third pharmaceutical compositions to the subject. Administering can include administering each of the first, second, and third pharmaceutical compositions simultaneously and wherein each of the first, second, and third pharmaceutical compositions has a different release profile for releasing the first second and third bacterial strains. Each of the first, second, and third bacterial strains can express a different therapeutic agent. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of n bacterial strains including at least first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the lysis plasmid of each of the n bacterial strains includes a toxin system, wherein the toxin system of the lysis plasmid of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the lysis plasmid of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Implementations of some methods can include one or more of the following features. The value of n can be 3. The value of n can be 4, 5, 6, 7, 8, 9, or 10. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of m pharmaceutical compositions, each including at least one of n bacterial strains, wherein the n bacterial strains comprise at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a toxin system, wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Also provided herein is a method for treating a disease in a subject in need thereof, including administering to the subject a therapeutically effective amount of each of m pharmaceutical compositions, each including at least one of n bacterial strains, wherein the n bacterial strains comprise at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain, wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain, wherein n can be at least 3, wherein each of the n strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the lysis plasmid of each of the n bacterial strains includes a toxin system, wherein the toxin system of the lysis plasmid of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain, wherein the toxin system of the lysis plasmid of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Implementations of some methods can include one or more of the following features. The value n can be 3. The value of n can be 4, 5, 6, 7, 8, 9, or 10. The value m=n. Each of the toxin systems can be independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof. Each of the second bacterial strain through the nth bacterial strain does not produce the second toxin of the toxin system of the previous strain, and the first bacterial strain does not produce the fourth toxin of the toxin system of the nth bacterial strain. Administering can include administering sequentially each of the n bacterial strains or m pharmaceutical compositions to the subject. Administering can include administering each of the m pharmaceutical compositions simultaneously and wherein each of the m pharmaceutical compositions has a different release profile for releasing the first second and third bacterial strains. Each of the first, second, and third bacterial strains can express a different therapeutic agent. The disease can be cancer or an infection. The infection can be caused by an infectious agent selected from the group consisting of:  Camphylobacter jejuni, Clostridium botulinium, Escherichia coli, Listeria monocytogenes  and  Salmonella.  The cancer can be selected from the group consisting of: glioblastoma, squamous cell carcinoma, breast cancer, colon cancer, hepatocellular cancer, melanoma, neuroblastoma, pancreatic cancer, and prostate cancer. 
     In some implementations of any one or more of the methods, bacterial strains, pharmaceutical compositions, systems, or kits described herein, one or more of the bacterial strains can express a therapeutic agent. In some implementations of any one or more of the methods, bacterial strains, pharmaceutical compositions, systems, or kits described herein, one or more of the bacterial strains expresses a therapeutic agent selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof. 
     Also provided herein is a method including culturing a first bacterial strain for a first period of time in a growth environment, adding a second bacterial strain to the growth environment and culturing the second bacterial strain for a second period of time, adding a third bacterial strain to the growth environment and culturing the third bacterial strain for a second period of time, wherein each of the first, second, and third bacterial strains includes a toxin system, wherein the toxin system of the first bacterial strain produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the toxin system of the second bacterial strain produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, and wherein the toxin system of the third bacterial strain produces a third toxin/third antitoxin pair and the second antitoxin from the second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the toxin system can be encoded on a plasmid, multiple plasmids, integrated into the host genome, or a combination thereof. 
     Implementations can include one or more of the following features. Each of the first, second, and third bacterial strains can include a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the quorum sensing molecule may or may not be different in each of the first, second, and third bacterial strains, wherein each quorum-sensing molecule of each of the first, second, and third bacterial strains may or may not have any effect on the activatable promoter of the lysis gene of another strain. Each of the lysis plasmids of the first, second, and third bacterial strains can be the plasmid containing the toxin system for such bacterial strain, or wherein each of the activator plasmids of the first, second, and third bacterial strains can be the plasmid containing the toxin system for such bacterial strain, or wherein the toxin system for each bacterial strain can be integrated into the genome. 
     Also provided herein is a method of culturing n bacterial strains including culturing a first bacterial strain of n bacterial strains for a first period of time in a culture, adding a second bacterial strain of the n bacterial strains to the culture and culturing the second bacterial strain for a second period of time, adding each of the other of then bacterial strains to the culture and culturing each such bacterial strain for a period of time, wherein n can be three or a greater whole number and wherein a plasmid of each of the n bacterial strains includes a toxin system, wherein the toxin system of the plasmid of the first bacterial strain produces a first toxin/first antitoxin pair and a nth antitoxin from an nth toxin/nth antitoxin pair wherein the first bacterial strain does not produce the nth toxin, wherein the toxin system of the plasmid of each mth, where m can be an element of the set {2, 3, . . . , n}, of the other bacterial strains in the n bacterial strains produces a mth toxin/mth antitoxin pair and the (m−1)th antitoxin from the (m−1)th toxin/(m−1)th antitoxin pair. 
     Implementations of some methods described herein can include one or more of the following features. Each of the n bacterial strains can include a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the quorum sensing molecule may or may not be different in each of the n bacterial strains, wherein each quorum-sensing molecule of each of the n bacterial strains may or may not have an effect on the activatable promoter of the lysis gene of another strain of then bacterial strains. Each of the lysis plasmids of the n strains can be the plasmid containing the toxin system for such bacterial strain. Each of the n bacterial strains can produce a payload. Each of the n bacterial strains can produce a different payload. Each of the n bacterial strains can produce the same payload. Each payload can be a therapeutic. The payload of the mth bacterial strain produces an mth substrate by directly or indirectly acting upon the substrate of the (m−1)th bacterial strain, and wherein the payload of the first bacterial strain acts upon a substrate present in the environment where the n bacterial strains are cultured. The value of n can be four. The value of n can be five. The value of n can be six. The method can further include culturing or co-culturing one or more additional bacterial strains in the culture. Each of the one or more additional bacterial strains can include a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the quorum sensing molecule can be different in each of the first, second, third, and one or more additional bacterial strains, wherein each quorum-sensing molecule of each of the first, second, third, and one or more additional bacterial strains can have no or substantially no effect on the activatable promoter of the lysis gene of another bacterial strain used in the culture. The lysis plasmid of each of the one or more additional bacterial strains can include a toxin system. The lysis plasmid and activator plasmid of each of the at least first, second, and third bacterial strains can be the same plasmid. The lysis plasmid and activator plasmid of each of the at least the first, second, and third bacterial strains can be separate plasmids. At least the first, second, and third bacterial strains can be metabolically competitive. At least the first, second, and third bacterial strains can be selected from  E. coli, S. typhimurium , or a bacterial variant thereof. Each of the at least the first, second, and third bacterial strains can not have a growth advantage compared to another strain in the culture. In each of the at least the first, second, and third bacterial strains, the lysis plasmid includes a lysis gene, an activatable promoter, and optionally a reporter gene, and the activator plasmid includes an activator gene, a degradation tag, and optionally a reporter gene. The lysis gene in each of the at least the first, second, and third bacterial strains can be E from a bacteriophage ΦX174. The activatable promoter in each of the at least the first, second, and third bacterial strains can be a LuxR-AHL activatable luxI promoter and the activator gene can be a LuxI. At least one reporter gene can be selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof. The degradation tag can be an ssrA-LAA degradation tag. At least one of the plasmids can be integrated into a genome of at least one of the first, second, and third bacterial strains. The culturing can occur in a designated growth environment. The culturing can occur in a microfluidic device. The culturing can occur in a bio reactor. The culturing can occur in vivo. Each of the bacterial strains can produce therapeutic payloads and the culturing can occur in a human or animal patient in need of the therapeutic payloads. Each of the first, second, and third periods of time can range from about 12 to about 72 hours. Each of the first, second, and third periods of time can range from about 1 hours to about n hours. Each of the first, second, and third periods of time can be selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours. Each of the n periods of time can partially or completely overlap. The n bacterial strains can be cultured together. Each of the n bacterial strains are added to the culture sequentially such that each mth bacterial strain can be added to the culture after the passage of the (m−1)th period of time. The first, second, and third periods of time can be selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours. 
     Also provided herein is a method of maintaining a co-culture, the method including co-culturing at least three bacterial strains, wherein each of the at least three bacterial strains includes a lysis plasmid having a lysis gene under the control of an activatable promoter, and an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, wherein both the activatable promoter of the lysis gene and the expression of the activator gene can be activated by the quorum sensing molecule, wherein the quorum sensing molecule can be different in each of the at least three bacterial strains, wherein each quorum-sensing molecule of each of the at least three bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another strain, wherein the lysis plasmid includes a toxin/antitoxin system. 
     Implementations of some methods described herein can have one or more of the following features. The toxin/antitoxin system can produce a toxin/antitoxin pair and a different antitoxin of another strain. The lysis plasmid and activator plasmid of each of the at least three bacterial strains can be the same plasmid. The lysis plasmid and activator plasmid of each of the at least three bacterial strains can be separate plasmids. The at least the three strains can be metabolically competitive. The at least three strains can be selected from  E. coli, S. typhimurium , or a bacterial variant thereof. Each of the at least three strains does not have a growth advantage compared to another strain. In each of the at least three strains, the lysis plasmid can include a lysis gene, an activatable promoter, and optionally a reporter gene, and the activator plasmid can include an activator gene, optionally a degradation tag, and optionally a reporter gene. The lysis gene in the at least three strains can be E from a bacteriophage ΦX174. The activatable promoter can be a LuxR-AHL activatable luxI promoter and the activator gene can be a LuxI. At least one reporter gene can be selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof. The degradation tag can be an ssrA-LAA degradation tag. The co-culture can be inoculated at a ratio of 1:1:1 of each of the at least three bacterial strains. At least one of the plasmids can be integrated into a genome of at least one of the at least three strains. The culturing occurs can occur a microfluidic device. The period of time can be 12 to 72 hours. The period of time can be selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours. The period of time can be selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours. The co-culturing of the at least three strains can be in a constant lysis state; wherein the constant lysis state is characterized by a steady-state balance of growth and lysis of the at least three bacterial strains. 
     The methods, systems, kits, bacterial strain, and compositions described herein can provide several advantages. First, a tri-lysis or multi-lysis system can ensure specific delivery of a therapeutic protein(s) via engineered strains for a certain amount of time until a subsequent strain in the system is administered, thereby separating the delivery of certain therapeutic protein(s) in space and time, as desired. This capability would not otherwise be available with the engineered bacteria approach to therapy since they colonize the sites of disease for extended periods of time, potentially resulting in a single therapeutic being delivered regardless of whether or not another strain has been introduced into the disease environment, as well as decreasing the colonization ability of future strains due to decreased resources in the disease environment used up by the strain that has been introduced earlier. 
     Second, the tri-lysis or multi-lysis system can also be engineered to output specific profiles of therapeutic proteins to the disease site. For example, the proteins produced by the three strains and the time in which they are allowed to colonize the site of disease may be adjusted depending on the context of the application. 
     Third, the tri-lysis or multi-lysis system can ensure the stability of the circuit components in the strains. This can be accomplished because subsequent strains in the tri-lysis cycle are able to kill off and remove the previous strain populating the site of disease, even if members of that population have mutated the circuit machinery. For example, strain A is administered and allowed to colonize the site of disease for a desired period of time, where members of the population have mutated the lysis gene (or any other gene critical to the function of the circuit). Then the introduction of strain B to the site of disease will allow for the de-population of strain A from the environment, including the mutated members of the population, since they do not carry an immunity for the toxin released by strain B. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Methods and materials are described herein for use in the present invention; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All publications, patent applications, patents, sequences, database entries, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. 
     Other features and advantages of the invention will be apparent from the following detailed description and figures, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a strategy to provide rapid and reliable control over active populations in a continuous culture.  FIG. 1A  is a schematic of a two strain system in which strain A has an engineered selective advantage over strain B using a paired toxin antitoxin system. Strain A produces toxin A, antitoxin A, and antitoxin B, while Strain B only produces toxin B and antitoxin B.  FIG. 1B  shows exemplary growth of strain B from  FIG. 1A  in a microfluidic cell chamber. After introduction of strain A via pulse loading (grey shaded region), fraction of Strain A increases exponentially while fraction of strain B decays. The images below the plot show a composite of phase contrast and fluorescence at the indicated time points. AU, arbitrary fluorescence units (background subtracted).  FIG. 1C  is an exemplary genetic diagram of a toxin antitoxin system integrated with the quorum sensing synchronized lysis circuit. The circuit contains a lysis plasmid containing the toxin, antitoxin system, and an activator/reporter plasmid. Transient production of LuxI eventually leads to an accumulation of AHL above the quorum threshold needed to activate LuxR, which begins a positive feedback loop by driving transcription off the PluxI promoters that control production of LuxI, reporter fluorescence protein (sfGFP, CFP or mKAte2) and the lysis gene X174E. LuxR in this system is driven by the native LuxR promoter.  FIG. 1D  is schematic of an exemplary two strain population dynamics with the integration of the synchronized lysis circuit to control population size. The self-limiting behavior of the synchronized lysis circuit, as well as the synchronization of toxin release when the primary strain is at its lowest population should enable more rapid strain takeover.  FIG. 1E  shows film strips showing a composite of phase contrast, GFP and CFP fluorescence produced by the oscillator circuit. The integration of the synchronized lysis circuit (bottom strip) reduces the time needed to achieve full takeover of the microfluidic trap compared to the non-synchronized lysis circuit strain (top strip). Note the sfGFP and CFP fluorescent reporters for the synchronized lysis strains are driven by production of AHL and are only expressed when quorum threshold is reached. 
         FIG. 2  shows an exemplary diagram of a three strain system that cycles between engineered strains unidirectionally.  FIG. 2A  is an exemplary schematic of a three-strain system of self-lysing  E. coli . Each strain produces its own toxin-antitoxin pair, while also producing the antitoxin of the following strain. All three strains utilize the same Lux AHL quorum sensing system to drive fluorescent reporter protein expression, as well as self-limiting synchronized lysis.  FIG. 2B  shows exemplary batch culture growth curves of the 3 strains shows the lysis OD600 of each strain. All strains were started from the same diluted density and under the same growth conditions (n=3).  FIG. 2C  shows exemplary lysis periods for the three strain system as measured in bilayer microfluidic chambers under the same growth conditions (n=15).  FIG. 2D  shows co-culture incubation of two strains seeded in microfluidic devices at initial concentrations of 20 percent dominant strain 80 percent susceptible strain. Strain takeover proceeds unidirectionally with the dominant strain taking over the microfluidic chamber.  FIG. 2E  shows video stills of a co-culture seeded at initial densities of 40 percent strain 1, 60 percent strain 2, exhibiting strain takeover by strain 1 in a bilayer microfluidic chamber.  FIG. 2F  shows Video stills of a co-culture seeded at initial densities of 40 percent strain 2, 60 percent strain 3, exhibiting strain takeover by strain 2 in a bilayer microfluidic chamber.  FIG. 2G  shows video stills of a co-culture seeded at initial densities of 40 percent strain 3, 60 percent strain 1, exhibiting strain takeover by strain 3 in a bilayer microfluidic chamber.  FIGS. 2H, 2I, and 2J  each show time series of fluorescence expression for the microfluidic experiments depicted in Figs. E-G demonstrating synchronized lysis of both strains and strain takeover within the microfluidic chamber. Fluorescent reporters for the synchronized lysis strains are driven by production of AHL and are only expressed when quorum threshold is reached. 
         FIG. 3  shows three-strain co-culture dynamics, model and experimental results.  FIG. 3A  shows time series dynamics of the colicin model demonstrate that when three-strains are simultaneously co-cultured and under estimated parameters, the three strains should each cycle once until a single strain overtakes the trap. The three graphs show the concentrations of the strains, colicins, and AHL over time.  FIG. 3B  shows time trace of GFP, CFP, and RFP fluorescence expression of a single trap from a 3-strain co-culture experiment in which all three strains are loaded at roughly equal ratios.  FIG. 3C  shows video stills of phase contrast, GFP, CFP, and RFP for the microfluidic chamber shown in  FIG. 3B .  FIG. 3D  shows time trace of GFP, CFP, and RFP fluorescence expression of a single trap from the experiment in  FIG. 3C  that demonstrates cycling through all 3 strains in a single continuous uninterrupted run.  FIG. 3D  shows time series dynamics of the colicin model demonstrate that when three-strains are simultaneously co-cultured and under estimated parameters, given constant seeding, the three strains should cycle indefinitely.  FIG. 3E  shows limit cycle of the three-strain system demonstrates stable transitions between the three strains. Additionally, all input parameters of reasonable value result in convergence towards the stable limit cycle.  FIG. 3F  shows diagram representing strain takeover events observed across 1600 microfluidic traps in which all three engineered strains are loaded simultaneously at approximately equal ratios. Arrows represent each possible transition event between the three strains, arrow colors indicate the number of observed transitions for each arrow. 
         FIG. 4  shows exemplary toxins that can be used according to some embodiments. 
         FIG. 5  shows exemplary verification of colicin and immunity activity in non-lysis strains in 96-well plate reader experiments.  FIG. 5A  shows MG1655 wild-type control strain with a mKate2 expression plasmid. Time course traces of OD600 and RFP fluorescence expression.  FIG. 5B  shows MG1655 wild-type control strain with a GFP expression plasmid. Time course traces of OD600 and GFP fluorescence expression (RFU).  FIG. 5C  shows MG1655 Strain 1 (pML0001) time course traces of OD600 and GFP fluorescence expression.  FIG. 5D  shows MG1655 Strain 2 time course traces of OD600 and RFP fluorescence expression.  FIG. 5E  shows MG1655 Strain 3 time course traces of OD600 and RFP fluorescence expression.  FIG. 5F  shows co-incubation of MG1655 Strain 1 with Colicin E3. Time course traces of OD600, GFP and RFP fluorescence (RFU) expression verify that Strain 1 is able to grow in the presence of Colicin E3.  FIG. 5G  shows co-incubation of MG1655 Strain 2 with Colicin E7. Time course traces of OD600 and GFP fluorescence (RFU) expression verify that Strain 1 is able to grow in the presence of Colicin E7.  FIG. 5H  shows co-incubation of MG1655 Strain 3 (pML0004) with Colicin V. Time course traces of OD600 and RFP fluorescence expression verify that Strain 3 is able to grow in the presence of Colicin V.  FIGS. 5I, 5J, and 5K  show co-incubation of Colicin E3, E7 and V with MG1655 wild type control strains demonstrate effectiveness of Colicins in inhibiting MG1655 wild type growth. Time course traces of OD600, GFP and RFP fluorescence (AU). 
         FIG. 6  shows video stills taken from exemplary microfluidic experiments to show growth inhibition of one strain by toxin production of the other strain. In this experiment, Strain 1 produces toxin 1, antitoxin 1, and antitoxin 3. Strain 3 produces toxin 3, antitoxin 3, and antitoxin 2. The inhibition of growth by toxins released by strain 1 is evident when comparing normal growth of Strain 3 (scenario 2) with the growth rate when Strain 1 is nearby (scenario 3). It is demonstrated that toxin activity is dependent on proximity, as shown in (Scenario 4), when the two strains are not in close proximity, growth of Strain 3 is not affected.  FIG. 6A  is scenario 1 showing the growth of Strain 1 alone in a microfluidic trap.  FIG. 6B  is scenario 2 showing the growth of Strain 3 alone in a microfluidic trap.  FIG. 6C  is scenario 3 showing the growth and Strain 1 and Strain 3 when they are in close proximity with each other. Growth of Strain 3 is inhibited by Strain 1.  FIG. 6D  is scenario 4 showing the growth of Strain 1 and Strain 3 when they are not in close proximity with each other.  FIG. 6E  and  FIG. 6F  shows fluorescence trajectories of the different scenarios in GFP and RFP. 
         FIG. 7  shows exemplary characterization of lysis strains in both plate reader and microfluidic experiments. Amplitude of oscillations of transmitted light in microfluidic experiments can vary due to phenotypic differences in the lysis event. For example, lysis events for strain 1 occur with more force, expelling cell lysate from the trap. However, lysis events for Strain 3 result in more buildup of cell lysate within the microfluidic trap.  FIG. 7A  shows plate reader OD 600  of Lysis for the 3 lysis strains and the corresponding expression of fluorescence (n=3).  FIG. 7B  shows overlay of Strain 1 fluorescence intensity normalized to max value (solid line) and transmitted light intensity normalized to max value (dashed line) of the microfluidic trap region (100×80×2 μm).  FIG. 7C  shows overlay of Strain 2 fluorescence intensity normalized to max value (solid line) and transmitted light intensity normalized to max value (dashed line) of the microfluidic trap region (100×80×2 μm).  FIG. 7D  shows overlay of Strain 3 fluorescence intensity normalized to max value (solid line) and transmitted light intensity normalized to max value (dashed line) of the microfluidic trap region (100×80×2 μm). 
         FIG. 8  shows deterministic modeling of an exemplary three-strain tri-lysis system.  FIG. 8A  shows magnitude of the non-zero eigenvalues of the map mode as a function of A c . The transition to oscillations occurs at A c =1.25 when λ 23=1.  FIG. 8B  shows number of lysis events per switching cycle near the Hopf bifurcation.  FIG. 8C  shows Hopf bifurcation diagram for the map model.  FIGS. 8D, 8E, 8F, and 8G  each show parameter sweeps evaluating dependences of the intervals between lysis events and the number of lysis events per switching cycle on system parameters in the oscillatory regime. 
         FIG. 9  shows roughly 1600 individual exemplary microfluidic traps from 4 separate 3-strain co-culture experiments that were analyzed. Microfluidic devices were simultaneously loaded with all 3 engineered strains, resulting in varying initial seeding cell concentrations of each microfluidic trap. Traps that demonstrate transitions between strains were recorded and shown in the above chart. The colors (gray, black, light gray) correspond to Strain 1, Strain 2, and Strain 3 respectively, and represent the dominant strain in the trap at the given time of the experiment.  FIG. 9A  shows transition events from Strain 1 (gray) to Strain 3 (light grey) over time.  FIG. 9B  shows transition events from Strain 2 (black) to Strain 1 (gray) over time.  FIG. 9C  shows transition events from Strain 3 (light grey) to Strain 2 (black) over time.  FIG. 9D  shows transition events from Strain 1 (gray) to Strain 3 (light grey) to Strain 2 (black) over time.  FIG. 9E  shows transition events from Strain 2 (black) to Strain 1 (gray) to Strain 3 (light grey) over time. 
         FIG. 10  shows exemplary strains and gene expression constructs found on each plasmid that can be used according to some embodiments. 
         FIG. 11  shows exemplary plasmids that can be used according to some embodiments. 
         FIG. 12  shows exemplary expansion of the function of plasmid stabilizing Toxin-antitoxin modules in multi-strain populations.  FIG. 12A  shows that in monoclonal populations, plasmid stabilizing toxin-antitoxin modules enable the killing of progeny cells that have mutated or lost the antitoxin gene. When expanded to a system of n&gt;1 strains, the strain that contains the TA module maintains self-stabilizing function, while gaining the added ability to kill any strain that does not have the antitoxin.  FIG. 12B  is a diagram showing that each strain produced its own toxin-antitoxin pair, while also producing the antitoxin of the following strain enabling sequential strain inhibition. Strain R contained toxin 1, antitoxin 1, and antitoxin 2. Strain P contained toxin 3, antitoxin 3, and antitoxin 1. Strain S contained toxin 2, antitoxin 2, and antitoxin 3.  FIG. 12C  is a general plasmid diagram of the RPS strains.  FIG. 12D  is a plot of batch culture growth rates of the engineered RPS and wild type  E. coli  MG1655 strains (n=3). All strains were started from the same diluted density and under the same growth conditions.  FIG. 12E  is a set of bar plots depicting the approximate population fractions over time for strain co-cultures seeded at an initial ratio of 1:2 dominant to susceptible (n=8). From top to bottom: (1) strain R (light gray) inhibits strain S (black); (2) strain S (black) inhibits strain P (gray); (3) strain P (gray) inhibits strain R (light gray).  FIG. 12F  is fluorescence microscopy images showing a composite of phase contrast, GFP, CFP, and RFP fluorescence. From left to right: (1) strain R (light gray) inhibits strain S (dark gray); (2) strain S (dark gray) inhibits strain P (gray); (3) strain P (gray) inhibits strain R (light gray). 
         FIG. 13  shows exemplary development of an engineered rock-paper-scissors ecology.  FIG. 13A  is a schematic of an exemplary two strain population dynamics with the integration of the SLC. Depicted is continuous synchronized population lysis during a strain takeover event.  FIG. 13B  is an exemplary genetic diagram of the quorum sensing synchronized lysis circuit and TA module. The first plasmid contained the X174E lysis protein driven by the luxI promoter, and corresponding toxin/antitoxin/antitoxin gene. A second ‘activator’ plasmid contained the luxI and LuxR genes driven by their native promoter pLuxI.  FIG. 13C  is a schematic showing that each strain produced its own toxin-antitoxin pair, while also producing the antitoxin of the following strain. All three strains utilized the same Lux-AHL quorum sensing system to drive fluorescent reporter protein expression, as well as self-limiting synchronized lysis.  FIG. 13D  shows a time series of fluorescence expression and video stills of a co-culture seeded at a 1:1 ratio strain 1 to strain 2, exhibiting strain takeover by strain 1 in a microfluidic chamber.  FIG. 13E  shows a time series of fluorescence expression and video stills of a co-culture seeded at a 1:1 ratio strain 2 to strain 3, exhibiting strain takeover by strain 2 in a microfluidic chamber.  FIG. 13F  shows a time series of fluorescence expression and video stills of a co-culture seeded at a 1:1 ratio strain 3 to strain 1, exhibiting strain takeover by strain 3 in a microfluidic chamber.  FIG. 13G  is a plot illustrating the limit cycle of the three-strain system demonstrates convergence to stable transitions between the three strains regardless of initial strain ratios.  FIG. 13H  is a diagram representing strain takeover events observed when all three engineered strains are cultured simultaneously. Arrows represent each possible transition event between the three strains, arrow shading indicates the number of observed transitions for each arrow. 
         FIG. 14  shows exemplary prolonging of circuit function in the absence of antibiotics.  FIG. 14A  is a schematic of scenario 1 depicting a system in which oscillations between growth phase and lysis transition to uncontrolled growth due to loss of circuit function. Scenario 2 depicts a cycle composed of the three-strain system in which the transition to the uncontrolled growth is prevented through the addition of the next strain of the system.  FIG. 14B  is a time trace of fluorescence expression for each of the strains shows the loss of circuit function over time. In accordance with scenario 1 from  FIG. 14A , each strain was cultured in the absence of kanamycin for a duration of 32 hours.  FIG. 14C  is boxplots depicting the time to loss of function for each strain (n=16).  FIG. 14D  In accordance with scenario 2 from  FIG. 14A , strains were loaded sequentially, starting with strain 2 and strain 1. Top—time trace of GFP, CFP, and RFP fluorescence expression of a single trap that demonstrates cycling through all 3 strains in a single continuous uninterrupted run. Bottom —video stills show a composite of phase contrast and fluorescence at the indicated time points. AU, arbitrary fluorescence units (background subtracted). 
         FIG. 15  shows exemplary RPS effect on a mutable genetic circuit.  FIG. 15A  illustrates Scenario 1, which depicts a system in which strain 1 was cultured in a 96 well plate for the duration of a single lysis event and passaged every 12 hours. Scenario 2 depicts a system in which strain 1 was cultured in a 96 well plate for the duration of a single lysis event and passaged every 12 hours. On every third passage the next strain of the RPS system is simultaneously added to the culture.  FIG. 15B  illustrates side-by-side comparison of each scenario (n=12) from  FIG. 15A  for a duration of 12 passages. Light gray squares represent functioning synchronized population lysis. Gray squares represent loss of synchronized population lysis. Dark gray squares represent loss of synchronized population lysis that was later recovered. Additionally, 12 corresponding samples from each scenario were Sanger sequenced across a 1000 base pair region containing the X174E lysis protein and Lux cassette. A check mark represents a correct sequence, (X) represents an incorrect sequence, and (i) represents an inconclusive sequencing read. All strains were started from the same diluted density and under the same growth conditions. 
         FIG. 16  shows exemplary verification of Colicin activity in non-lysis strains in 96-well plate reader experiments.  FIG. 16A  is a time course trace of OD 600  for MG1655 wild-type  E. coli .  FIG. 16B  is a time course trace of OD 600  for MG1655 wild-type  E. coli  co-incubated with filtered lysate of Colicin V producing strain.  FIG. 16C  is a time course trace of OD 600  for MG1655 wild-type  E. coli  co-incubated with filtered lysate of Colicin E7 producing strain.  FIG. 16D  is a time course trace of OD 600  for MG1655 wild-type  E. coli  co-incubated with filtered lysate of Colicin E3 producing strain. 
         FIG. 17  shows exemplary characterization of strains in both plate reader and microfluidic experiments.  FIG. 17A  is a plot of plate reader OD 600  of lysis for the 3 lysis strains and the corresponding expression of fluorescence (n=3).  FIG. 17B  is a plot overlaying Strain 1 fluorescence intensity normalized to max value (solid line) and transmitted light intensity normalized to max value (dashed line) of the microfluidic trap region (100×80×1.2 μm).  FIG. 17C  is a plot overlaying Strain 2 fluorescence intensity normalized to max value (solid line) and transmitted light intensity normalized to max value (dashed line) of the microfluidic trap region (100×80×1.2 μm).  FIG. 17D  is a plot overlaying Strain 3 fluorescence intensity normalized to max value (solid line) and transmitted light intensity normalized to max value (dashed line) of the microfluidic trap region (100×80×1.2 μm). 
         FIG. 18  shows exemplary co-culture incubation of strain pairs in microfluidic devices.  FIG. 18A  is a bar plot showing that each pair of strains was co-cultured at a 1:1 ratio dominant (bold) to susceptible (italic) (n=35). For each strain pair, the dominant strain displaced the susceptible strain in 100% of culture regions.  FIG. 18B  is a bar plot showing that each pair of strains was co-cultured at a 1:5 ratio dominant (bold) to susceptible (italic) (n=396). For each strain pair the dominant strain displaced the susceptible strain in 100%, 100%, and 92% of culture regions. 
         FIG. 19  shows exemplary time series dynamics of the colicin model assuming the system is closed to the introduction of new cells. The three graphs show the concentrations of the strains, colicins, and AHL over time when strain 3 initially starts at a higher concentration and there is no introduction of new cells. 
         FIG. 20  shows exemplary three-strain co-culture dynamics.  FIG. 20A  is a time trace of GFP, CFP, and RFP fluorescence expression of a single trap from a 3-strain co-culture experiment in which all three strains are loaded at roughly equal ratios.  FIG. 20B  shows video stills of phase contrast, GFP, CFP, and RFP for the microfluidic chamber shown in  FIG. 20A . 
         FIG. 21  shows exemplary plasmids that can be used according to some embodiments. 
         FIG. 22  shows exemplary toxins that can be used according to some embodiments. 
         FIG. 23  shows exemplary strains that can be used according to some embodiments. 
         FIG. 24  shows exemplary dynamics of the colicin model for γ A =1, γ C =0.2, α=1, β=1, δ=0.02, A c =1, ε=0.001.  FIG. 24A  shows an exemplary time series.  FIG. 24B  shows an exemplary map of P i , Q i , R i . 
         FIG. 25  shows exemplary dynamics of the colicin model for γ A =10, γ C =1, α=10, β=1, δ=0.02, A c =100, ε=0.001.  FIG. 25A  shows an exemplary time series.  FIG. 25B  shows an exemplary map of P i , Q i , R i . 
         FIG. 26  shows exemplary dynamics of the colicin model for γ A =10, γ C =1, α=10, β=20, δ=0.01, A c =100, ε=0.02.  FIG. 26A  shows an exemplary time series.  FIG. 26B  shows an exemplary map of P i , Q i , R i . 
     
    
    
     DETAILED DESCRIPTION 
     Population control is a powerful tool in synthetic biology. Control of microbial communities has been achieved in a few systems over the last decade. Until now, population control can be categorized as two systems. The first, involves a single strain community that exhibits self-limiting population density. The mechanisms behind these systems utilize bacterial quorum sensing systems such as the LuxI/LuxR AHL systems. When cells grow to a certain density and reach ‘quorum’ they drive the production of a toxic or lysis inducing protein. A second category can be classified as two strain populations in which the strains exhibit predator-prey behavior, oscillatory behavior, or maintain a constant ratio between the two strains. Two strain systems, much like single strain systems rely on quorum sensing in order to drive production of a toxin or lysis protein in either strain. For example, in a predator prey model, a two-way quorum sensing system is used in order to drive production of toxic proteins in the prey, only when the predator is present. Other mechanisms of two strain systems include the use of orthogonal quorum sensing systems such as Lux and Las, to drive oscillating lysis events between two strains, which then oscillate in population density over a duration of time. 
     Advances in synthetic biology have led to an arsenal of proof-of-principle bacterial circuits that can be leveraged for applications ranging from therapeutics to bio-production. A unifying challenge for most applications is the presence of selective pressures that lead to high mutation rates for engineered bacteria. A common strategy is to develop cloning technologies aimed to increase the fixation time for deleterious mutations in single cells. Provided herein is a complimentary approach that is guided by ecological interactions, whereby cyclical population control is engineered to stabilize the functionality of intracellular gene circuits. 
     Over the past two decades, synthetic biologists have developed sophisticated molecular circuitry to control the activity of individual cells (see, e.g., M. B. Elowitz, S. Leibler,  Nature  403, 335 (2000); T. S. Gardner, C. R. Cantor, J. J. Collins,  Nature  403, 339 (2000); J. Hasty, D. McMillen, J. J. Collins,  Nature  420, 224 (2002); L. You, R. S. Cox III, R. Weiss, F. H. Arnold,  Nature  428, 868 (2004); P. E. Purnick, R. Weiss,  Nature reviews Molecular cell biology  10, 410 (2009); H. H. Wang, et al.,  Nature  460, 894 (2009); S. Ausländer, D. Ausländer, M. Müller, M. Wieland, M. Fussenegger,  Nature  487, 123 (2012); P. Siuti, J. Yazbek, T. K. Lu,  Nature biotechnology  31, 448 (2013); T. H. Segall-Shapiro, E. D. Sontag, C. A. Voigt,  Nature biotechnology  36, 352 (2018)). Over time, such systems inevitably lose function due to evolutionary selection pressures that lead to runaway mutations (see, e.g., F. K. Balagaddé, L. You, C. L. Hansen, F. H. Arnold, S. R. Quake,  Science  309, 137 (2005)). Approaches to this challenge include the integration of recombinant elements into the host genome (see, e.g., M. Y. Peredelchuk, G. N. Bennett, Gene 187, 231 (1997)), or use of plasmid stabilizing elements (see, e.g., K. Gerdes,  Nature Biotechnology  6, 1402 (1988)), synthetic “kill switches” (see, e.g., C. T. Chan, J. W. Lee, D. E. Cameron, C. J. Bashor, J. J. Collins,  Nature chemical biology  12, 82 (2016)), or synthetic amino acids (see, e.g., D. J. Mandell, et al.,  Nature  518, 55 (2015); A. J. Rovner, et al.,  Nature  518, 89 (2015); N. Ostrov, et al.,  Science  353, 819 (2016); J. W. Lee, C. T. Chan, S. Slomovic, J. J. Collins,  Nature chemical biology p.  1 (2018)). Although stabilizing elements can prolong the march to mutation, evolution will inevitably render stabilizing elements ineffective (see, e.g., F. K. Balagaddé, L. You, C. L. Hansen, F. H. Arnold, S. R. Quake,  Science  309, 137 (2005)). This is particularly true in the case of in vivo applications where delivery of antibiotics is difficult (see, e.g., W. C. Ruder, T. Lu, J. J. Collins,  Science  333, 1248 (2011); M. A. Fischbach, J. A. Bluestone, W. A. Lim,  Science translational medicine  5, 179ps7 (2013); D. T. Riglar, P. A. Silver,  Nature Reviews Microbiology  16, 214 (2018); M. O. Din, et al.,  Nature  536, 81 (2016); A. P. Teixeira, M. Fussenegger,  Current opinion in biotechnology  47, 59 (2017); B. P. Landry, J. J. Tabor,  Microbiology spectrum  5 (2017)), or where the interruption of plasmid function is particularly problematic (see, e.g., J. Shong, M. R. J. Diaz, C. H. Collins,  Current Opinion in Biotechnology  23, 798 (2012)). Described herein is how a small ecology can be engineered to stabilize gene circuit functionality in a manner that complements genetic engineering at the single cell level. Rather than housing stabilizing elements within a single strain, the components of stability are decoupled to different subpopulations of an ecological system such that a runaway mutation in one strain would not cause the stabilizing ecology to fail. 
     Over the past decade, the field of synthetic biology has advanced from engineering single cells to engineering whole populations. Described herein are three-strain (or more) population control systems and methods that can cycle continuously over a long period of time, which has not previously been achieved. Now, the tri-lysis or multi-lysis system presents a new paradigm of multi-population dynamic control (circuitry within an ecology instead of circuitry within a cell) that opens exciting new possibilities for engineered synthetic systems. These multi-strain systems may enable scientists to achieve complex interactions that may not have been possible previously through the engineering of single cells or single populations. 
     Disclosed herein are methods, materials and circuits/devices/systems that pertain to a multi-strain ‘tri-lysis’ or ‘multi-lysis’ microbial system. A “rock paper scissors” system provides a unique solution to the synthetic biology problems of plasmid loss or mutation of burdensome circuits caused by selective pressures. For example, three strains of  E. coli  can be designed such that each strain could kill, or be killed by one of the other two strains. The resulting “rock-paper-scissors” ecology demonstrates rapid cycling of strains in microfluidic devices and leads to a significant increase in the stability of gene circuit functionality in cell culture. This can be accomplished by the tri-lysis or multi-lysis system because subsequent strains in the tri-lysis or multi-lysis cycle are able to kill off and remove the previous strain population, even if members of that population have mutated the circuit machinery. A ‘tri-lysis’ or ‘multi-lysis’ system uses at least three strains of bacteria to complementarily kill off each strain in a cyclical or time-specific manner. For example, strain A is administered and allowed to colonize a region, over a period of time the population may begin to mutate a lysis gene (or any other gene critical to the function of the circuit). As another example, strain A is administered and allowed to colonize a region, over a period of time, the population may begin to mutate a gene of interest (e.g., a gene encoding a heterologous nucleic acid and/or protein, such as, e.g., a therapeutic agent or a payload). Then the introduction of strain B to the ecosystem will allow for the de-population of strain A from the environment, including the mutated members of the population, since they do not carry an immunity for the toxin released by strain B. The use of a system as provided herein as a method to ensure circuit stability has many broadened applications in the fields of therapeutics, production, and sensing applications. As used herein, ‘lysis’ includes the process of breaking down a cell in a manner that compromises its integrity, as well as any process that kills a cell. Exemplary processes of cellular death encompassed by ‘lysis’ include, e.g., expression of a lysis gene, the action of a toxin, and the like. In some exemplary embodiments, cell death by toxin can occur through the process of breaking down a cell in a manner that compromises its integrity. In some embodiments, a toxin can initiate cell death without the process of breaking down a cell. 
     Any of the toxin systems described herein can be replaced by an appropriate cell death system. In some cases, a cell death system can include different pairs of materials (e.g., analogous to a toxin an antitoxin). In yet other cases, the different characteristics of adjacent or sequential bacterial strains can be specific to the prior strain (e.g., a strain can produce a material specific and detrimental for the prior strain, but it is not harmed by such material itself because of some different characteristic in comparison with the prior strain). Additional exemplary pairs of materials that can be used herein are as follows: (i) antibiotic peptides or antimicrobial peptides and host defense peptides (e.g., derived from bacterial, fungal, or animal sources); (ii) systems that include bacteriophages that are specific to a particular to a prior strain that is earlier in the cycle, e.g., sequential delivery of bacteriophages by the bacteria to clear out the previous strain, where the bacteriophages are specific to that previous strain; (iii) systems that include delivery of prodrugs that kill the previous strain upon enzymatic activation by a bacterial protein specific to that previous strain; (iv) systems that include use of different bacterial strains in the cycle where each bacterial strain is a natural predator of the prior strain in the cycle, (for example,  Acinetobacter  (predator) and  E. coli  (prey); (v) a system where each strain produces the same single toxin, but orthogonal quorum sensing is used to activate toxin expression in the previous strain, (e.g., where production of such toxin the prior strain is activated by the presence of another strain (via that other strain&#39;s quorum sensing molecules) such as an orthogonal quorum system that initiates production of toxin or lysis protein in the n−1 strain when the n strain is added). Moreover, in some embodiments, instead of an expressed antitoxin, the toxin system can use toxins (or other types of cell death systems, such as those described herein) that are specific to certain bacterial species and not to other strains. In such cases, instead of expressing an antitoxin, the toxin (or other types of cell death systems, such as those described herein)-expressing bacteria can have characteristics that render it insensitive to the toxin (or other types of cell death systems, such as those described herein) it produces that is specific to other strains. For example, one could use different bacterial species that can be targeted with different species-specific toxins (for example,  E coli  followed by  Salmonella ) where the  Salmonella  produces an antimicrobial peptide specific to the  E coli  (for example, colicins only kill  E. coli  and not  Salmonella ). In such systems the analog of the antitoxin is a subsequent strain&#39;s inherent insensitivity to the toxin it expresses that is specific to the species of the prior strain. Similarly, other characteristics of a bacterial strain can constitute an appropriate cell death system, such as where one strain is a gram positive bacterium followed by a gram negative bacterial strain that produces as a toxin (or other types of cell death systems, such as those described herein) that is specific to gram positive bacteria, and the analog of the antitoxin in gram negative bacterial is its status of not being a gram positive bacterial strain. In yet other cases, an analog of a bacterial strain&#39;s antitoxin may be the presence or absence of certain surface receptors or cellular import/export systems in comparison with other bacterial strains, e.g., an  E. coli  strain could have a receptor necessary for the toxicity of a toxin (or other types of cell death systems, such as those described herein) expressed by the following  E. coli  strain that lacks that receptor, such as  E. coli  expressing SdaC/DcrA receptor (which is necessary for colicin V to be toxic) followed by an  E. coli  strain that does not express SdaC/DcrA receptor but does express colicin V (in such case the non-expression of the SdaC/DcrA receptor in the second strain would be analogous to an antitoxin. In certain embodiments, the foregoing variations on the concept of a toxin system may be combined such that not all bacterial strains in the cycle of the invention need to use the same type of toxin system or combination of toxin/antitoxin pairs. It will be appreciated that any appropriate combination of toxin systems and cell death systems can be used. 
     Additionally, the tri-lysis or multi-lysis system also ensures specific delivery of a therapeutic protein(s) via engineered strains for a certain amount of time until a subsequent strain in the system is administered, thereby separating the delivery of certain therapeutic protein(s) in space and time, as desired. This capability would not otherwise be available with the engineered bacteria approach to therapy since they colonize the sites of disease for extended periods of time, potentially resulting in a single therapeutic being delivered regardless of whether or not another strain has been introduced into the disease environment, as well as decreasing the colonization ability of future strains due to decreased resources in the disease environment used up by the strain that has been introduced earlier. 
     As used herein the term “co-culture” or “co-culturing” refers to growing or culturing two or more (e.g., three or more) distinct cell types (e.g., at least two distinct bacterial strains or at least three bacterial strains) within a single recipient or environment (e.g., a single cell culture vessel, a single cell culture plate, a single bioreactor, a single microfluidic device, or a single subject (e.g., in vivo)). In some cases, co-culturing can include growing or culturing two or more (e.g., three or more) distinct cell types at the same time. In some cases, co-culturing can include growing or culturing two or more (e.g., three or more) distinct cell types within a single recipient over a period of time (e.g., growing a first cell type, followed by growing a second cell type, followed by growing a third cell type, where the growing periods may or may not overlap). In some embodiments, co-culturing can include growing or culturing two or more (e.g., three or more) distinct cell types within a single recipient over a period of time, wherein the growing periods of each of the distinct cell types partially overlap. 
     A variety of different methods known in the art can be used to introduce any of the plasmids disclosed herein into a bacterial cell (e.g., a Gram negative bacterial cell, a Gram positive bacterial cell). Non-limiting examples of methods for introducing nucleic acid into a cell include: transformation, microinjection, electroporation, cell squeezing, sonoporation. Skilled practitioners will appreciate that the plasmids described herein can be introduced into any cell provided herein. 
     The term “treat(ment),” is used herein to denote delaying the onset of, inhibiting, alleviating the effects of, or prolonging the life of a subject suffering from disease, e.g., a cancer, an infection. 
     The terms “effective amount” and “amount effective to treat” as used herein, refer to an amount or concentration of a composition or treatment described herein, at least three bacterial strains, utilized for a period of time (including acute or chronic administration and periodic or continuous administration) that is effective within the context of its administration for causing an intended effect or physiological outcome. For example, effective amounts of at least three bacterial strains that express and/or secrete a therapeutic agent (e.g., any of the therapeutic agents described herein) for use in the present disclosure include, for example, amounts that inhibit the growth of a cancer, e.g., tumor cells and/or tumor-associated immune cells, improve or delay tumor growth, improve survival for a subject suffering from or at risk of developing cancer, and improving the outcome of other cancer treatments. As another example, effective amounts of at least three bacterial strains that express and/or secrete a therapeutic agent (e.g., any of the therapeutic agents described herein) can include amounts that advantageously affect a tumor microenvironment. 
     The term “subject” (used interchangeably with “patient”) is used throughout the specification to describe an animal, human or non-human, to whom treatment according to the methods of the present disclosure is provided. Veterinary applications are clearly anticipated by the present disclosure. The term includes but is not limited to birds, reptiles, amphibians, and mammals, e.g., humans, other primates, pigs, rodents, such as mice and rats, rabbits, guinea pigs, hamsters, horses, cows, cats, dogs, sheep and goats. Preferred subjects are humans, farm animals, and domestic pets such as cats and dogs. In some embodiments, the subject is a human. For example, in any of the methods described herein, the subject can be at least 2 years or older (e.g., 4 years or older, 6 years or older, 10 years or older, 13 years or older, 16 years or older, 18 years or older, 21 years or older, 25 years or older, 30 years or older, 35 years or older, 40 years or older, 45 years or older, 50 years or older, 60 years or older, 65 years or older, 70 years or older, 75 years or older, 80 years or older, 85 years or older, 90 years or older, or 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, 18, 20, 21, 24, 25, 27, 28, 30, 33, 35, 37, 39, 40, 42, 44, 45, 48, 50, 52, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 100, 101, 102, 103, or 104 years old). 
     The term “population” when used before a noun means two more of the specific noun. For example, the phrase “a population of bacterial strains” can mean three or more bacterial strains. 
     The term “cancer” refers to cells having the capacity for unlimited autonomous growth. Examples of such cells includes cells having an abnormal state or condition characterized by rapidly proliferating cell growth. The term is meant to include cancerous growths, e.g., tumors, oncogenic processes, metastatic tissues, malignantly transformed cells. 
     A metastatic tumor can arise from a multitude of primary tumor types, including but not limited to those of prostate, colon, lung, breast, bone and liver origin. Metastases develop, e.g., when tumor cells shed, detach or migrate from a primary tumor, enter the vascular system, penetrate into surrounding tissues, and grow to form tumors at distinct anatomical sites, e.g., sites separate from a primary tumor. 
     Individuals considered at risk for developing cancer may benefit from the present disclosure, e.g., because prophylactic treatment can begin before there is any evidence and/or diagnosis of the disorder. Individuals “at risk” include, e.g., individuals exposed to carcinogens, e.g., by consumption (e.g., by inhalation and/or ingestion), at levels that have been shown statistically to promote cancer in susceptible individuals. Also included are individuals at risk due to exposure to ultraviolet radiation, or their environment, occupation, and/or heredity, as well as those who show signs of a precancerous condition such as polyps. Similarly, individuals in very early stages of cancer or development of metastases (i.e., only one or a few aberrant cells are present in the individual&#39;s body or at a particular site in an individual&#39;s tissue) may benefit from such prophylactic treatment. 
     Skilled practitioners will appreciate that a subject can be diagnosed, e.g., by a medical professional, e.g., a physician or nurse (or veterinarian, as appropriate for the subject being diagnosed), as suffering from or at risk for a condition described herein, e.g., cancer, using any method known in the art, e.g., by assessing a subject&#39;s medical history, performing diagnostic tests, and/or by employing imaging techniques. 
     Skilled practitioners will also appreciate that treatment need not be administered to a subject by the same individual who diagnosed the subject (or the same individual who prescribed the treatment for the subject). Treatment can be administered (and/or administration can be supervised), e.g., by the diagnosing and/or prescribing individual, and/or any other individual, including the subject her/himself (e.g., where the subject is capable of self-administration). 
     Also provided herein are methods of generating a recombinant bacterial cell that can express and/or secrete a therapeutic agent (e.g., any of the therapeutic agents described herein) that include: a nucleic acid encoding the therapeutic agent to be produced in the recombinant bacterial cell, and optionally, a plasmid-stabilizing element, wherein the plasmid-stabilizing element is a toxin/antitoxin system; and culturing the recombinant bacterial cell under conditions sufficient for the expression and/or secretion of the toxin, antitoxin and therapeutic agent. Also provided herein are methods of generating a recombinant bacterial cell that can express and/or secrete a therapeutic agent (e.g., any of the therapeutic agents described herein) that include: introducing into a bacterial cell a lysis plasmid, an activator plasmid, a nucleic acid encoding the therapeutic agent to be produced in the recombinant bacterial cell, and a plasmid-stabilizing element; and culturing the recombinant bacterial cell under conditions sufficient for the expression and/or secretion of the toxin, antitoxin and therapeutic agent. In some embodiments, the plasmid stabilizing element is a toxin/antitoxin system. In some embodiments, the plasmid stabilizing element may be expressed in the lysis plasmid. In some embodiments, the toxin/antitoxin system may produce a toxin/antitoxin pair and a different antitoxin of another strain. In some embodiments, the introducing step can include introducing into a recombinant bacterial cell an expression vector including a nucleic acid encoding the therapeutic agent to be produced into a recombinant bacterial cell. In some embodiments, the bacterial cell is an  E. coli  cell, a  S. typhimurium  cell, or a bacterial variant thereof. In some embodiments, the bacterial strain is a Gram-negative bacterial strains, e.g., a  Salmonella  strain, an  Acetobacter  strain, an  Enterobacter  strain, a  Fusobacterium  strain, a  Helicobacter  strain, a  Klebsiella  strain, or an  E. coli  strain. In some embodiments, the bacterial strain is a Gram-positive bacterial strain, e.g., a  Actinomyces  strain, a  Bacillus  strain, a  Clostridium  strain, an  Enterococcus  strain, or a  Lactobacillus  strain. In some embodiments, the at least three bacterial strains are all Gram negative bacterial strains or all Gram positive strains. In some embodiments, at least one of the at least three bacterial strains is a Gram negative bacterial strain. In some embodiments, at least one of the at least three bacterial strains is a Gram positive bacterial strain. 
     Methods of culturing bacterial cells are well known in the art, and examples of such methods are provided in the Examples. Bacterial cells can be maintained in vitro under conditions that favor proliferation and growth. Briefly, bacterial cells can be cultured by contacting a bacterial cell (e.g., any bacterial cell described herein) with a cell culture medium that includes the necessary growth factors and supplements to support cell viability and growth. 
     Methods of introducing nucleic acids and expression vectors into a bacterial cell are known in the art. For example, transformation can be used to introduce a nucleic acid into a bacterial cell. In some embodiments, the bacterial cell can include any of the plasmids described herein. 
     Provided herein is a bacterial strain comprising a toxin system (also called a toxin/antitoxin system) including a toxin/antitoxin pair (e.g., the antitoxin is effective against the toxin). In some embodiments, the toxin system can produce a toxin/antitoxin pair and a different antitoxin of another strain. A toxin system can be included (e.g., encoded) in any appropriate location. In some embodiments, a toxin system can be included in the genome of a bacterial strain. In some embodiments, a toxin system can be included in one or more plasmids. In some embodiments, a toxin system can be partially included in the genome and partially included in one or more plasmids. In some embodiments, a toxin system can be included on a lysis plasmid. In some embodiments, a toxin system can be included on an activator plasmid. In some embodiments, a toxin system can be included on a third plasmid. A third plasmid can be any appropriate plasmid. In some embodiments, a toxin system can be genetically engineered, or naturally occurring in a bacterial strain. In some embodiments, the toxin system can be inserted into a bacterial strain. 
     The toxin system can be any appropriate toxin system. In some embodiments, a toxin system includes a first toxin/first antitoxin pair (e.g., the first antitoxin is effective against the first toxin) and a second antitoxin. In some embodiments, a bacterial strain encoding such a toxin system does not encode a second toxin against which the second antitoxin is effective. 
     In some embodiments, the toxin/antitoxin system may be type I toxin/antitoxin system, type II toxin/antitoxin system, type II toxin/antitoxin system, type IV toxin/antitoxin system, type V toxin/antitoxin system, or type VI toxin/antitoxin system. Non-limiting examples of type I toxin/antitoxins include Hok and Sok, Fst and RNAII, TisB and IstR, LdrB and RdlD, FlmA and FlmB, Ibs and Sib, TxpA/BrnT and RatA, SymE and SymR, and XXCV2162 and ptaRNA1. Non-limiting examples of type II toxin/antitoxins include CcdB and CcdA; ParE and ParD; MaxF and MazE; yafO and yafN; HicA and HicB; Kid and Kis; Zeta and Epsilon; DarT and DarG. For example, type III toxin/antitoxin systems include interactions between a toxic protein and an RNA antitoxin, e.g., ToxN and ToxI. For example, type IV toxin/antitoxin systems include toxin/antitoxin systems that counteract the activity of the toxin and the two proteins do not directly interact. An example of a type V toxin/antitoxin system is GoT and GoS. An example of a type VI toxin/antitoxin system is SocA and SocB. 
     In some embodiments, the toxin/antitoxin system may be replaced by a bacteriocin/immunity protein system. As used herein, the term “toxin/antitoxin” includes both the toxin/antitoxin systems described herein above, including bacteriocin/immunity protein systems. Bacteriocins are ribosomally-synthesized peptides that are produced by bacteria. Bacteriocins are non-toxic to bacteria that produce the bacteriocins and are generally toxic to other bacteria. Typically, a bacterium that produces a bacteriocin also produces an immunity protein that can inhibit or prevent the toxic effect of the bacteriocin. Accordingly, a bacteriocin and a corresponding immunity protein can be used in an analogous fashion to a toxin/antitoxin system as described herein. Most bacteriocins are extremely potent, and exhibit antimicrobial activity at nanomolar concentrations. By way of example, eukaryotic produced microbials have 10 2  to 10 3  lower activities (Kaur and Kaur (2015) Front. Pharmacol. doi: 10.3389/fphar.2015.00272). 
     Non-limiting examples of bacteriocins that can be included in any of the bacteria strains, systems and methods described herein include: acidocin, actagardine, agrocin, alveicin, aureocin, aureocin A53, aureocin A70, bisin, carnocin, carnocyclin, caseicin, cerein, circularin A, colicin, curvaticin, divercin, duramycin, enterocin, enterolysin, epidermin/gallidermin, erwiniocin, gardimycin, gassericin A, glycinecin, halocin, klebicin, lactosin S, lactococcin, lacticin, leucoccin, lysostaphin, macedocin, mersacidin, mesentericin, microbisporicin, microcin S, mutacin, nisin, paenibacillin, planosporicin, pediocin, pentocin, plantaricin, pneumocyclicin, pyocin, reutericin 6, sakacin, salivaricin, sublancin, subtilin, sulfolobicin, tasmancin, thuricin 17, trifolitoxin, variacin, vibriocin, warnericin, cytolisin, pyocyn S2, colicin A, colicin E1, microcin MccE492, and warnerin. 
     In some embodiments, the bacteriocin is obtained from a Gram negative bacteria (e.g., microcins (e.g., microcin V of  E coli , subtilosin A from  B. subtillis ), colicins (E.g., colicin produced by and toxic to certain strains of  E. coli  (e.g., colicin A, colicin B, colicin E1, colicin E3, colicin E5, and colicin E7), tailocins (e.g., R-type pyocins, F-type pyocins)). 
     In some embodiments, the bacteriocin is obtained from a Gram positive bacteria (e.g., class I bacteriocins (e.g., Nisin, lantibiotics), class II bacteriocins (e.g., IIa pediocin-like bacteriocins, IIb bacteriocins (e.g., lactococcin G), IIc cyclic peptides (e.g., enterocin AS-48), IId single peptide bacteriocins (e.g., aureocin A53), class III bacteriocins (e.g., Ma (e.g., bacteriolysins), and IIIb (which kill the target by disrupting the membrane potential), or class IV bacteriocins (e.g., complex bacteriocins containing lipid or carbohydrate moieties)). 
     Any of the bacterial systems described herein can further include a lysis plasmid and an activator plasmid. The lysis plasmid and activator plasmid can each independently include any appropriate components. The lysis plasmid and the activator plasmid can be based on any appropriate existing plasmid. 
     The lysis plasmid can include a lysis gene, an activatable promoter, and optionally a reporter gene. In some embodiments, the lysis gene can be operably linked to the activatable promoter. In some embodiments, the reporter gene can be operably linked to the activatable promoter. In some embodiments, both the lysis gene and the reporter gene can be operably linked to a single copy of the activatable promoter. In some embodiments, both the lysis gene and the reporter gene can be independently operably linked to separate copies of the activatable promoter. 
     The activator plasmid can include an activator gene, optionally a degradation tag, and optionally a reporter gene. In some embodiments, the activatable promoter in the activator plasmid is the same activatable promoter as in the lysis plasmid. In some embodiments, the activatable promoter in the activator plasmid is activated by the same mechanism as the activatable promoter in the lysis plasmid (e.g., by the same quorum-sensing molecule, directly or indirectly). The activator gene can, in some embodiments, promote the accumulation of a quorum-sensing molecule (e.g., the activator gene can encode a protein in the biosynthetic pathway of the quorum-sensing molecule). In some embodiments, the activator gene is operatively linked to an activatable promoter. 
     A quorum-sensing molecule can be any appropriate quorum-sensing molecule. In some embodiments, the quorum-sensing molecule can be an N-acyl homoserine lactone (AHL). In some embodiments, the quorum-sensing molecule can be a homoserine lactone (HSL) or a homolog thereof. In some embodiments, a quorum-sensing molecule can be an auto-inducing peptide (AIP) from a Gram-positive bacteria. Other quorum-sensing molecules are known in the art. 
     An activatable promoter can be any appropriate activatable promoter. In some embodiments, the activatable promoter can be activated, directly or indirectly, by the quorum-sensing molecule. In this way, in some embodiments, a feedback loop can be set up such that the presence of the quorum-sensing molecule drives accumulation of the quorum-sensing molecule. In some embodiments of any of the bacterial strains described herein, the activatable promoter is an AHL-activatable promoter. In some embodiments of any of the bacterial strains described herein, the activatable promoter is a LuxR-AHL activatable luxI promoter. In some embodiments, the activatable promoter is a RpaR-AHL activatable RpaI promoter. In some embodiments, the activatable promoter is a TraR-HSL activatable traI promoter. Other activatable promoters are known in the art. 
     A lysis gene can be any appropriate lysis gene. In some embodiments of any of the bacterial strains described herein, the lysis gene is E from a bacteriophage ΦX174. In some embodiments, the lysis gene is the col E1 Lysis protein. Other lysis genes are known in the art. 
     An activator gene can be any appropriate activator gene. In some embodiments, the activator gene is a LuxI. In some embodiments, the activator gene is a RpaI. In some embodiments, the activator gene is TraI Other activator genes are known in the art. 
     In some embodiments, the quorum-sensing molecule is an AHL, the activatable promoter is a LuxR-AHL activatable luxI promoter, and the activator gene is a LuxI. 
     In some embodiments, the quorum-sensing molecule is an AHL, the activatable promoter is a RpaR-AHL activatable RpaI promoter, and the activator gene is a RpaI. 
     In some embodiments, the quorum-sensing molecule is a HSL, the activatable promoter is a TraR-HSL activatable traI promoter, and the activator gene is a TraI. 
     A reporter gene can be any appropriate reporter gene. In some embodiments, the reporter gene can be a fluorescent protein (e.g., green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP) or a variant thereof). In some embodiments, the reporter gene can be an enzyme (e.g., β-galactosidase). Other reporter genes are known in the art. 
     A degradation tag can be any appropriate degradation tag. In some embodiments, the degradation tag is an ssrA-LAA degradation tag. Other degradation tags are known in the art. 
     In some embodiments, a bacterial strain can encode an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein (e.g., a payload)) operably linked to a promoter. In some embodiments, the additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein) operably linked to a promoter is encoded on a plasmid. The plasmid can be any appropriate plasmid. In some embodiments, the plasmid be a lysis plasmid or an activator plasmid. An additional nucleic acid and/or protein can be any appropriate nucleic acid and/or protein. For example, an additional nucleic acid and/or protein can be a therapeutic agent. Any appropriate promoter can be used. In some embodiments, the promoter can be an activatable promoter. In some embodiments, the promoter can be a promoter that is activated, directly or indirectly, by the quorum sensing molecule. In some embodiments, the promoter can be an activatable promoter as described above. In some embodiments, the promoter can be a constitutive promoter. Many constitutive promoters are known in the art. A therapeutic agent can be any appropriate therapeutic agent. In some embodiments, a therapeutic agent can be any of the therapeutic agents described herein. For example, in some embodiments, a therapeutic agent can be selected from the group consisting of: an inhibitory nucleic acid (e.g., siRNA, shRNA, miRNA, or antisense (e.g., antisense DNA, antisense RNA, or a synthetic analog)), a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, and an antibody or antigen-binding fragment thereof. In some embodiments, an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein) may be secreted, exocytosed, or otherwise exported from a bacterial strain as described herein. In some embodiments, an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein) may be released upon lysis of a bacterial strain as described herein. In some embodiments, an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein) may be displayed on the surface a bacterial strain as described herein. 
     In some embodiments, an additional nucleic acid and/or protein (e.g., payload) encoded by a bacterial strain can act upon an additional nucleic acid and/or protein (or a product thereof) encoded by a previous (e.g., immediately previous) bacterial strain in a tri-lysis or multi-lysis system. In some embodiments, a payload of an m th  bacterial strain (e.g., one of the n bacterial strains) can produce an m th  substrate by directly or indirectly acting upon the substrate of the (m−1) th  bacterial strain, and the payload of the first bacterial strain can act upon a substrate present in the environment where the n bacterial strains are cultured. 
     Provided herein are systems that include two or more (e.g., three or more) bacterial strains as described herein. In some embodiments, a system as described can be a multi-lysis system. In some embodiments, such systems can include 3 bacterial strains. In some embodiments, such systems can include 4, 5, 6, 7, 8, 9, 10, or more bacterial strains. 
     In some embodiments, when an activator plasmid/lysis plasmid system is used, the quorum-sensing molecule of each of the bacterial strains in the system can be different. In some embodiments, the quorum-sensing molecule of each of the bacterial strains in the system can have no or substantially no effect on the activatable promoter of the lysis gene of another strain. In some embodiments, the quorum sensing molecule can be the same in each of the bacterial strains. In some embodiments, the lysis plasmid of each of the bacterial strains can be copies of the same plasmid. In some embodiments, activator plasmid of each of the bacterial strains can be copies of the same plasmid. In some embodiments, the lysis plasmid of each of the bacterial strains can be different plasmids. In some embodiments, the activator plasmid of each of the bacterial strains can be different plasmids. In some embodiments, two or more (e.g., 3, 4, 5, 6, 7, 8, 9, 10, or more) of bacterial strains can be metabolically competitive. In some embodiments, the bacterial strains can be selected from  E. coli, S. typhimurium , or a bacterial variant thereof. In some embodiments none of the bacterial strains have a growth advantage compared to another strain in the system. 
     In some systems that include more than one bacterial strain, all bacterial strains can encode an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein). In some systems that include more than one bacterial strain, no bacterial strains can encode an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein). In some systems that include more than one bacterial strain, some bacterial strains can encode an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein), while some do not. In systems that include more than one bacterial strain encoding an additional nucleic acid and/or protein (e.g., a heterologous nucleic acid and/or protein), the encoded additional nucleic acid and/or protein of each such bacterial strain is independently selected (e.g., all such bacterial strains can encode a different additional nucleic acid and/or protein, all such bacterial strains can encode the same additional nucleic acid and/or protein, or some such bacterial strains can encode the same additional nucleic acid and/or protein, while others encode one or more different additional nucleic acids and/or proteins). 
     A multi-lysis system can have include appropriate number of strains. A tri-lysis system can include three strains (this can also be called a “rock, paper, scissors” (RPS) ecology). In such a system, each strain can encode a toxin/antitoxin pair and a secondary antitoxin, such that the strain can kill a previous strain in the cycle (e.g., the secondary antitoxin encoded by the previous strain is not effective against the toxin of the instant strain, and the secondary antitoxin encoded by the instant strain is effective against the toxin of the previous strain) and be killed by a subsequent strain in a cycle (e.g., the secondary antitoxin encoded by the instant strain is not effective against the toxin of the subsequent strain, and the secondary antitoxin encoded by the subsequent strain is effective against the secondary toxin of the instant strain. An exemplary tri-lysis system is shown in  FIG. 12B . 
     In some embodiments, a multi-lysis system can include at least three strains (e.g., at least four, five, six, or more strains). In some embodiments, a multi-lysis system can have n strains, including a first strain, a second strain, and an n th  strain. In some such cases, the second strain to the n th  strain can each have a previous strain, based on the numbering of the strains (e.g., the previous strain for the second strain is the first strain). In some such cases, each of the second through n−1 th  strains have a subsequent strain (e.g., the subsequent strain of the n−1 th  strain is the n th  strain). In some such cases, each of the second strain through the n th  strain encodes a first toxin that is effective against the previous strain, a first antitoxin to the first toxin, and a second antitoxin to the toxin produced by the previous strain. In some such cases, the first strain encodes a first toxin that is effective against the n th  strain, a first antitoxin to the first toxin, and a second antitoxin to the toxin produced by the n th  strain. The value of n can be any appropriate value. In some embodiments, n can be at least 3 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more). 
     Also provided herein are methods of co-culturing at least three (e.g., at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least eleven, at least twelve, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12) bacterial strains (e.g., any of the bacterial strains described herein). In some embodiments, co-culturing can include inoculating a culture with at least two (e.g., at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least eleven, at least twelve, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12) bacterial strains (e.g., any of the bacterial strains described herein), initially inoculated at a ratio of inoculation. A ratio of inoculation can be any appropriate ratio. In some embodiments, a ratio of inoculation of at least one bacterial strain to at least one other bacterial strain can be 1:1 (e.g., for three strains, the ratio can be 1:1:1). In some embodiments, a ratio of inoculation of at least one bacterial strain to at least one other bacterial strain can be 1:2 (e.g., for three strains, the ratio can be 1:2:m, 2:1:m, 1:m:2, 2:m:1, m:1:2, m:2:1). In some embodiments, a ratio of inoculation of at least one bacterial strain to at least one other bacterial strain can be 1:5 (e.g., for three strains, the ratio can be 1:5:m, 5:1:m, 1:m:5, 5:m:1, m:1:5, m:5:1). In some embodiments, a ratio of inoculation of at least one bacterial strain to at least one other bacterial strain can be 1:10 (e.g., for three strains, the ratio can be 1:10:m, 10:1:m, 1:m:10, 10:m:1, m:1:10, m:10:1). The value of m can be any appropriate value. For example, in some embodiments, m can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more. 
     In some embodiments, co-culturing can include, sequentially, beginning a culture with a first bacterial strain, culturing for a period of time, adding a second bacterial strain, and culturing for a period of time. As used herein, sequentially can include a particular order of culturing two or more strains. In some embodiments, sequentially can include completely overlapping periods of time (e.g., growth periods), partially overlapping periods of time, and/or non-overlapping periods of time. In some embodiments, one or more growth periods can overlap while other growth periods in the same system can be non-overlapping. In some embodiments, all growth periods in a given system can be overlapping or non-overlapping. In some embodiments, one or more additional bacterial strains can be sequentially cultured in the same manner as the second bacterial strain. In this way, a sequential co-culture can be performed with partially overlapping growth periods. In some embodiments, the first bacterial strain can be added to the culture containing the second bacterial strain and cultured for a period of time, and optionally followed, in an alternating fashion, by the second bacterial strain and the first bacterial strain. In this way, an alternating co-culture can be performed with partially overlapping growth periods. Additions of bacterial strains can be performed at any appropriate inoculation ratio, where the inoculation ratio is based on the population(s) of cells in the culture. For example, in some embodiments, the inoculation ratio can be any of the inoculation ratios described herein. 
     In some embodiments, co-culturing can include, sequentially, beginning a culture with a first bacterial strain, culturing for a period of time, adding a second bacterial strain, culturing for a period of time, adding a third bacterial strain, and culturing for a period of time. In some embodiments, one or more additional bacterial strains can be sequentially cultured in the same manner as the second and bacterial strains. In this way, a sequential co-culture can be performed with partially overlapping growth periods. In some embodiments, a cyclical co-culture with partially overlapping growth periods can be performed by adding the first bacterial strain to the culture containing the third (or the one or more additional bacterial strains), cultured for a period of time, followed by the sequential addition and culturing of the second bacterial strain, the third bacterial strain, and the one or more additional bacterial strains, in the same order as was carried out initially. Additions of bacterial strains can be performed at any appropriate inoculation ratio, where the inoculation ratio is based on the population(s) of cells in the culture. For example, in some embodiments, the inoculation ratio can be any of the inoculation ratios described herein. 
     In some embodiments, a bacterial strain that is added to a culture can reduce the population of or eliminate one or more bacterial strains present in the culture. For example, a second bacterial strain can, in some embodiments, reduce the population of or eliminate the first bacterial culture. 
     In some embodiments, a period of time for the culture (e.g., a growth period) of any of the bacterial strains described herein can be between 1 hour to 35 days (e.g., 1 hour to 30 days, 1 hour to 28 days, 1 hour to 26 days, 1 hour to 25 days, 1 hour to 24 days, 1 hour to 22 days, 1 hour to 20 days, 1 hour to 18 days, 1 hour to 16 days, 1 hour to 14 days, 1 hour to 12 days, 1 hour to 10 days, 1 hour to 8 days, 1 hour to 7 days, 1 hour to 6 days, 1 hour to 5 days, 1 hour to 4 days, 1 hour to 72 hours, 1 hour to 70 hours, 1 hour to 68 hours, 1 hour to 66 hours 1 hour to 64 hours, 1 hour to 62 hours, 1 hour to 60 hours, 1 hour to 58 hours, 1 hour to 56 hours, 1 hour to 54 hours, 1 hour to 52 hours, 1 hour to 50 hours, 1 hour to 48 hours, 1 hour to 46 hours, 1 hour to 44 hours, 1 hour to 40 hours, 1 hour to 38 hours, 1 hour to 36 hours, 1 hour to 34 hours, 1 hour to 32 hours, 1 hour to 30 hours, 1 hour to 28 hours, 1 hour to 26 hours, 1 hour to 24 hours, 1 hour to 22 hours, 1 hour to 20 hours, 1 hour to 18 hours, 1 hour to 16 hours, 1 hour to 14 hours, 1 hour to 12 hours, 1 hour to 10 hours, 1 hour to 8 hours, 1 hour to 6 hours, 1 hour to 4 hours, 1 hour to 2 hours, 2 hours to 35 days, 2 hours to 30 days, 2 hours to 28 days, 2 hours to 26 days, 2 hours to 25 days, 2 hours to 24 days, 2 hours to 22 days, 2 hours to 20 days, 2 hours to 18 days, 2 hours to 16 days, 2 hours to 14 days, 2 hours to 12 days, 2 hours to 10 days, 2 hours to 8 days, 2 hours to 7 days, 2 hours to 6 days, 2 hours to 5 days, 2 hours to 4 days, 2 hours to 72 hours, 2 hours to 70 hours, 2 hours to 68 hours, 2 hours to 66 hours 2 hours to 64 hours, 2 hours to 62 hours, 2 hours to 60 hours, 2 hours to 58 hours, 2 hours to 56 hours, 2 hours to 54 hours, 2 hours to 52 hours, 2 hours to 50 hours, 2 hours to 48 hours, 2 hours to 46 hours, 2 hours to 44 hours, 2 hours to 40 hours, 2 hours to 38 hours, 2 hours to 36 hours, 2 hours to 34 hours, 2 hours to 32 hours, 2 hours to 30 hours, 2 hours to 28 hours, 2 hours to 26 hours, 2 hours to 24 hours, 2 hours to 22 hours, 2 hours to 20 hours, 2 hours to 18 hours, 2 hours to 16 hours, 2 hours to 14 hours, 2 hours to 12 hours, 2 hours to 10 hours, 2 hours to 8 hours, 2 hours to 6 hours, 2 hours to 4 hours, 4 hours to 35 days, 4 hours to 30 days, 4 hours to 28 days, 4 hours to 26 days, 4 hours to 25 days, 4 hours to 24 days, 4 hours to 22 days, 4 hours to 20 days, 4 hours to 18 days, 4 hours to 16 days, 4 hours to 14 days, 4 hours to 12 days, 4 hours to 10 days, 4 hours to 8 days, 4 hours to 7 days, 4 hours to 6 days, 4 hours to 5 days, 4 hours to 4 days, 4 hours to 74 hours, 4 hours to 70 hours, 4 hours to 68 hours, 4 hours to 66 hours 4 hours to 64 hours, 4 hours to 64 hours, 4 hours to 60 hours, 4 hours to 58 hours, 4 hours to 56 hours, 4 hours to 54 hours, 4 hours to 54 hours, 4 hours to 50 hours, 4 hours to 48 hours, 4 hours to 46 hours, 4 hours to 44 hours, 4 hours to 40 hours, 4 hours to 38 hours, 4 hours to 36 hours, 4 hours to 34 hours, 4 hours to 34 hours, 4 hours to 30 hours, 4 hours to 28 hours, 4 hours to 26 hours, 4 hours to 24 hours, 4 hours to 24 hours, 4 hours to 20 hours, 4 hours to 18 hours, 4 hours to 16 hours, 4 hours to 14 hours, 4 hours to 14 hours, 4 hours to 10 hours, 4 hours to 8 hours, 4 hours to 6 hours, 6 hours to 35 days, 6 hours to 30 days, 6 hours to 28 days, 6 hours to 26 days, 6 hours to 25 days, 6 hours to 24 days, 6 hours to 22 days, 6 hours to 20 days, 6 hours to 18 days, 6 hours to 16 days, 6 hours to 14 days, 6 hours to 12 days, 6 hours to 10 days, 6 hours to 8 days, 6 hours to 7 days, 6 hours to 6 days, 6 hours to 5 days, 6 hours to 4 days, 6 hours to 76 hours, 6 hours to 70 hours, 6 hours to 68 hours, 6 hours to 66 hours 6 hours to 64 hours, 6 hours to 66 hours, 6 hours to 60 hours, 6 hours to 58 hours, 6 hours to 56 hours, 6 hours to 54 hours, 6 hours to 56 hours, 6 hours to 50 hours, 6 hours to 48 hours, 6 hours to 46 hours, 6 hours to 44 hours, 6 hours to 40 hours, 6 hours to 38 hours, 6 hours to 36 hours, 6 hours to 34 hours, 6 hours to 36 hours, 6 hours to 30 hours, 6 hours to 28 hours, 6 hours to 26 hours, 6 hours to 24 hours, 6 hours to 26 hours, 6 hours to 20 hours, 6 hours to 18 hours, 6 hours to 16 hours, 6 hours to 14 hours, 6 hours to 16 hours, 6 hours to 10 hours, 6 hours to 8 hours, 12 hours to 35 days, 12 hours to 30 days, 12 hours to 28 days, 12 hours to 26 days, 12 hours to 25 days, 12 hours to 24 days, 12 hours to 22 days, 12 hours to 20 days, 12 hours to 18 days, 12 hours to 16 days, 12 hours to 14 days, 12 hours to 12 days, 12 hours to 10 days, 12 hours to 8 days, 12 hours to 7 days, 12 hours to 6 days, 12 hours to 5 days, 12 hours to 4 days, 12 hours to 72 hours, 12 hours to 70 hours, 12 hours to 68 hours, 12 hours to 66 hours 12 hours to 64 hours, 12 hours to 62 hours, 12 hours to 60 hours, 12 hours to 58 hours, 12 hours to 56 hours, 12 hours to 54 hours, 12 hours to 512 hours, 12 hours to 50 hours, 12 hours to 48 hours, 12 hours to 46 hours, 12 hours to 44 hours, 12 hours to 40 hours, 12 hours to 38 hours, 12 hours to 36 hours, 12 hours to 34 hours, 12 hours to 312 hours, 12 hours to 30 hours, 12 hours to 28 hours, 12 hours to 26 hours, 12 hours to 24 hours, 12 hours to 22 hours, 12 hours to 20 hours, 12 hours to 18 hours, 12 hours to 16 hours, 12 hours to 14 hours, 1 day to 35 days, 1 day to 30 days, 1 day to 28 days, 1 day to 26 days, 1 day to 25 days, 1 day to 24 days, 1 day to 22 days, 1 day to 20 days, 1 day to 18 days, 1 day to 16 days, 1 day to 14 days, 1 day to 12 days, 1 day to 10 days, 1 day to 8 days, 1 day to 6 days, 1 day to 5 days, 1 day to 4 days, 1 day to 3 days, 1 day to 2 days, 2 days to 35 days, 2 days to 30 days, 2 days to 28 days, 2 days to 26 days, 2 days to 25 days, 2 days to 24 days, 2 days to 22 days, 2 days to 20 days, 2 days to 18 days, 2 days to 16 days, 2 days to 15 days, 2 days to 14 days, 2 days to 12 days, 2 days to 10 days, 2 days to 8 days, 2 days to 6 days, 2 days to 4 days, 2 days to 3 days, 4 days to 35 days, 4 days to 30 days, 4 days to 28 days, 4 days to 26 days, 4 days to 25 days, 4 days to 24 days, 4 days to 22 days, 4 days to 20 days, 4 days to 18 days, 4 days to 16 days, 4 days to 15 days, 4 days to 14 days, 4 days to 12 days, 4 days to 10 days, 4 days to 8 days, 4 days to 6 days, 7 days to 35 days, 7 days to 30 days, 7 days to 28 days, 7 days to 26 days, 7 days to 25 days, 7 days to 24 days, 7 days to 22 days, 7 days to 20 days, 7 days to 18 days, 7 days to 16 days, 7 days to 15 days, 7 days to 14 days, 7 days to 12 days, 7 days to 10 days, 7 days to 8 days, 14 days to 35 days, 14 days to 30 days, 14 days to 28 days, 14 days to 26 days, 14 days to 25 days, 14 days to 24 days, 14 days to 22 days, 14 days to 20 days, 14 days to 18 days, 14 days to 16 days, 14 days to 15 days, 21 days to 35 days, 21 days to 30 days, 21 days to 28 days, 21 days to 26 days, 21 days to 25 days, 21 days to 24 days, 21 days to 22 days, 28 days to 35 days, or 28 days to 30 days; 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 10 days, 12 days, 14 days, 16 days, 18 days, 20 days, 21 days, 22 days, 24 days, 25 days, 26 days, 28 days, 30 days, 32 days, 34 days or 35 days). 
     The length of a cycle can be modulated by an appropriate method. For example, the length of a cycle can be regulated by using strains that lyse at different ODs. Cell lysis can also be regulated by tuning the internal circuitry of the quorum sensing components, e.g., tuning of AHL degradation, tuning lysis of protein degradation, tuning of promoters to increase or decrease expression of molecules involved in the quorum sensing circuitry. 
     Various methods known in the art can be used to determine whether the quorum threshold is reached. For example, the quorum threshold can be measured using traditional protein quantification methods to measure the level of AHL expression in the culture medium. The quorum threshold can also be measured using reporter proteins driven by the luxI promoter. In some embodiments, the reporter protein is a fluorescent protein, a bioluminescent luciferase reporter, a secreted blood/serum or urine reporter (e.g., secreted alkaline phosphatase, soluble peptides, Gaussian luciferase). 
     Various methods are known in the art to determine and/or measure cell lysis. For example, cell lysis can be determined phenotypically using a microscopy by the change in intensity of transmitted light and/or absorbance at various wavelengths including 600 nm light. In some embodiments, bacterial cell lysis is synchronized. In other embodiments, bacterial cell lysis is not synchronized. Synchronized lysis can be measured via optical density at 600 nm absorbance (OD 600 ) in a plate reader or other quantitative instruments. 
     In some embodiments of any of the bacterial strains described herein, the therapeutic agent is selected from the group consisting of: an inhibitory nucleic acid (e.g., siRNA, shRNA, miRNA, or antisense), a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin (e.g., a diphtheria toxin, a gelonin toxin, anthrax toxin), an antimicrobial peptide, and an antibody or antigen-binding fragment thereof. Non-limiting examples of cytokines include filgrastim, an interleukin, an interferon (e.g., IFNb-1b), and a transforming growth factor beta. Non-limiting examples of enzymes include asparaginase, glucarpidase, β-glucocerebrosidase, elosulfase alfa, asfotase-alfa, and sebelipase alfa. Non-limiting examples of peptide hormones include metreleptin, parathyroid hormone, and insulin. Non-limiting examples of fusion proteins include albiglutide, dulaglutide, a factor IX Fc-fusion, and a factor VIII Fc-fusion. Non-limiting examples of clotting factors include factor IX, factor VIII, and factor XIII A subunit. Non-limiting examples of antibodies or antigen-binding fragments thereof include belimumab, ipilimumab, belatacept, brentuximab, afilbercept, pertuzumab, raxibacumab, trastuzumab, golimumab, bevacizumab, obinutuzumab, ramucirumab, siltuximab, rituximab, adalimumab, vedolizumab, pembrolizumab, blintumomab, nivolumab, secukinumab, dinutuximab, alirocumab, evolocumab, idarucizumab, mepolizumab, daratumumab, necitumumab, elotuzumab, obiltoxaximab, ixekizumab, reslizumab, infliximab, atezolizumab, daclizumab, ustekinumab and etanercept. In some embodiments, the therapeutic agent can be a Cl esterase inhibitor. In some embodiments, the therapeutic agent can be a von Willebrand factor. 
     Provided herein are pharmaceutical compositions comprising any one or more of the bacterial strains as described herein. In some embodiments, the pharmaceutical composition is formulated for in situ drug delivery. 
     Provided herein is also a system that can include a co-culture of at least two bacterial strains as described herein (e.g., at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least eleven, at least twelve, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12). 
     Provided herein is also a drug system comprising one or more systems as described herein. 
     Provided herein is also a periodic drug system comprising one or more systems as described herein. 
     Provided herein is also a kit comprising one or more bacterial strains as described herein. 
     Provided herein is also a kit comprising one or more systems as described herein. 
     Provided herein are methods of treating a disease in a subject (e.g., a cancer, an infectious disease, an autoimmune disorder, a genetic disorder, a metabolic disorder). Exemplary methods include administering to a subject in need of treatment therapeutically effective amounts of any one or more of the bacterial strains described herein, or any one or more of the pharmaceutical compositions described herein, or any one or more of the systems described herein to thereby treat the disease in the subject. For example, provided herein is a method of treating a disease in a subject comprising administering to the subject a therapeutically effective amount of each of n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain. Each of the second bacterial strain to the n th  bacterial strain can have a previous bacterial strain. The value of n can be at least 3. Each of then strains can include a toxin system as described herein. In some cases, the toxin system each of the second through n th  bacterial strains independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain. The toxin system of the first bacterial strain can produce a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. In some embodiments, one or more of the n strains can include lysis plasmid described herein and/or an activator plasmid as described herein. The value of n can be any appropriate value. In some embodiments, n can be at least 3 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more). 
     Provided herein are methods of treating a disease in a subject (e.g., a cancer, an infectious disease, an autoimmune disorder, a genetic disorder, a metabolic disorder). Exemplary methods include administering to a subject in need of treatment therapeutically effective amounts of a pharmaceutical composition including any one or more of the bacterial strains described herein, or any one or more of the pharmaceutical compositions described herein, or any one or more of the systems described herein to thereby treat the disease in the subject. For example, provided herein is a method of treating a disease in a subject comprising administering to the subject a therapeutically effective amount of m pharmaceutical compositions, each comprising one or more of n bacterial strains including at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain. Each of the second bacterial strain to the n th  bacterial strain can have a previous bacterial strain. The value of n can be at least 3. The value of m can be at least 3. The value of m can be equal to the value of n. Each of the n strains can include a toxin system as described herein. In some cases, the toxin system each of the second through n th  bacterial strains independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain. The toxin system of the first bacterial strain can produce a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. In some embodiments, one or more of the n strains can include lysis plasmid described herein and/or an activator plasmid as described herein. The value of n can be any appropriate value. In some embodiments, n can be at least 3 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more). The value of m can be any appropriate value. In some embodiments, m can be at least 3 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more). 
     Administering can include any appropriate schedule. For example, administering can include a schedule that is effective for co-culturing as described herein. In some embodiments, administering can include a schedule that is effective for co-culturing including partially overlapping growth periods, as described herein. In methods described herein, administering can include administering at least two (e.g., at least three) bacterial strains to the subject. 
     Also provided herein are methods of treating a disease in a subject (e.g., a cancer, an infectious disease, an autoimmune disorder, a genetic disorder, a metabolic disorder) that include administering to a subject in need of treatment therapeutically effective amounts of a first bacterial strain (e.g., any of the bacterial strains described herein) for a first period of time, administering therapeutically effective amounts of a second bacterial strain (e.g., any of the bacterial strains described herein) for a second period of time, and administering therapeutically effective amounts of a third bacterial strain (e.g., any of the bacterial strains described herein) for a third period of time. 
     In some embodiments of any of the methods described herein, the n bacterial strains (e.g., the first, the second and the third bacterial strains) are different bacterial strains that each express and/or secrete a different therapeutic agent (e.g., any of the therapeutic agents described herein). In some embodiments of any of the methods described herein, the n bacterial strains (e.g., the first, the second and the third bacterial strains) are different bacterial strains that each express and/or secrete the same therapeutic agent (e.g., any of the therapeutic agents described herein). In some embodiments of any of the methods described herein, the n bacterial strains (e.g., the first, the second and the third bacterial strains) are different bacterial strains that may or may not each express and/or secrete the same or a different therapeutic agent (e.g., any of the therapeutic agents described herein) (e.g., two strains can express and/or secrete one therapeutic agent, and a third strain can express and/or secrete a different therapeutic agent). The value of n can be any appropriate value. In some embodiments, n can be at least 3 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more). 
     In some embodiments of any of the methods described herein, the n bacterial strains (e.g., the first, the second and the third bacterial strains) do not express or secrete a therapeutic agent (e.g., any of the therapeutic agents described herein). In some embodiments of any of the methods described herein, then bacterial strains (e.g., the first, the second and the third bacterial strains) produce a bacteriocin (e.g., any of the bacteriocins described herein). The value of n can be any appropriate value. In some embodiments, n can be at least 3 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more). 
     In some embodiments of any of the methods described herein, administering includes a cycle of treatment, and the cycle of treatment is repeated at least two times (e.g., at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, at least 10 times, at least 11 times, at least 12 times). 
     In some embodiments of any of the methods described herein, the first, the second, and the third time period can be between 1 hour and 35 days (e.g., between 1 hour and 28 days, between 1 hour and 21 days, between 1 hour and 14 days, between 1 hour and 7 days, between 1 hour and 5 days, between 1 hour and 3 days, between 1 hour and 2 days, between 1 hour and 1 day, between 1 day and 35 days, between 1 day and 28 days, between 1 day and 21 days, between 1 day and 14 days, between 1 day and 7 days, between 1 day and 5 days, between 1 day and 3 days, between 1 day and 2 days, between 7 days and 35 days, between 7 days and 28 days, between 7 days and 14 days, between 7 days and 10 days, between 14 days and 35 days, between 14 days and 28 days, between 14 days and 21 days, between 21 days and 35 days, between 21 days and 28 days, between 21 days and 24 days, or between 28 days and 35 days). 
     In some aspects of any of the methods described herein, the first, the second and the third time period of time are similar in length, e.g., the same length of time. 
     In other aspects of any of the methods described herein, the first, the second and the third time period of time are not the same length of time. In some aspects, the first and the third period of times are the same. In some aspects, the first and the third period of times are not the same. In some aspects, the first and the second period of times are the same. In some aspects, the first and the second period of times are not the same. In some aspects, the second and the third period of times are the same. In some aspects, the second and the third period of times are not the same. 
     In some embodiments of any of the methods described herein, a growth period can be between 1 hour and 35 days (e.g., between 1 hour and 28 days, between 1 hour and 21 days, between 1 hour and 14 days, between 1 hour and 7 days, between 1 hour and 5 days, between 1 hour and 3 days, between 1 hour and 2 days, between 1 hour and 1 day, between 1 day and 35 days, between 1 day and 28 days, between 1 day and 21 days, between 1 day and 14 days, between 1 day and 7 days, between 1 day and 5 days, between 1 day and 3 days, between 1 day and 2 days, between 7 days and 35 days, between 7 days and 28 days, between 7 days and 14 days, between 7 days and 10 days, between 14 days and 35 days, between 14 days and 28 days, between 14 days and 21 days, between 21 days and 35 days, between 21 days and 28 days, between 21 days and 24 days, or between 28 days and 35 days). 
     In some aspects of any of the methods described herein, the growth period of each of the n bacterial strains is about the same. In some embodiments of any of the methods described herein, the growth period of one or more of the n bacterial strains is different from one or more of the other bacterial strains. 
     In some embodiments of any of the methods described herein, administering includes administering sequentially each of the at least three bacterial strains to the subject. In some embodiments of any of the methods described herein, administering includes administering sequentially each of the n bacterial strains to the subject. 
     In some embodiments of any of the methods described herein, administering includes administering each of the at least three bacterial strains simultaneously. In some embodiments of any of the methods described herein, administering includes administering each of the n bacterial strains simultaneously. 
     In some embodiments of any of the methods described herein, the subject has a cancer or an infection. 
     In some embodiments wherein the subject has a cancer, the cancer can be, e.g., a primary tumor, or a metastatic tumor. 
     In some embodiments, the cancer is a non-T-cell-infiltrating tumor. 
     In some embodiments of any of the methods described herein, the cancer is selected from the group consisting of: glioblastoma, squamous cell carcinoma, breast cancer, colon cancer, hepatocellular cancer, melanoma, neuroblastoma, pancreatic cancer, and prostate cancer. Treatment of multiple cancer types at the same time is contemplated by and within the present disclosure. 
     In some instances, the subject having the cancer may have previously received cancer treatment (e.g., any of the cancer treatments described herein). 
     In some embodiments of any of the methods described herein, the subject has an infection (e.g., an infectious disease). In some embodiments of any of the methods described herein, the infection is caused by an infectious agent selected from the group consisting of:  Camphylobacter jejuni, Clostridium botulinium, Escherichia coli, Listeria monocytogenes  and  Salmonella.    
     In some embodiments, strain A, or a first strain, is first introduced to the site of culture or colonization, for a specified period of time, to deliver its payload of therapeutic protein(s). Then a second strain, strain B, can be introduced, which produces a toxin to kill and remove strain A, and then Strain B can deliver its payload of therapeutic protein(s) for a specified period of time. Then a third strain, strain C, can be introduced, which will kill and remove strain B, and then deliver its payload of therapeutic protein(s) for a specified period of time. Then strain A can be re-introduced to repeat the cycle. This system is not limited to a three strain system, it can potentially be composed of more than three strains where each strain produces a toxin with the ability to kill another strain in the system which does not have the anti-toxin, thereby allowing a cyclical system (composed of four, five, six, or more strains). 
     Administering may be performed, e.g., at least once (e.g., at least 2-times, at least 3-times, at least 4-times, at least 5-times, at least 6-times, at least 7-times, at least 8-times, at least 9-times, at least 10-times, at least 11-times, at least 12-times, at least 13-times, or at least 14-times) a week. Also contemplated are monthly treatments, e.g., administering at least once per month for at least 1 month (e.g., at least two, three, four, five, or six or more months, e.g., 12 or more months), and yearly treatments (e.g., administration once a year for one or more years). Administration can be via any art-known means, e.g., intravenous, subcutaneous, intraperitoneal, oral, topical, and/or rectal administration, or any combination of known administration methods. 
     As used herein, treating includes “prophylactic treatment”, which means reducing the incidence of or preventing (or reducing the risk of) a sign or symptom of a disease (e.g., a cancer, an infection) in a subject at risk of developing a disease (e.g., a cancer, an infection). The term “therapeutic treatment” refers to reducing signs or symptoms of a disease, e.g., reducing cancer progression, reducing severity of a cancer, and/or re-occurrence in a subject having cancer, reducing inflammation in a subject, reducing the spread of an infection in a subject. 
     The methods described herein can be used in cancer treatments. Non-limiting examples of cancer include: acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), adrenocortical carcinoma, anal cancer, appendix cancer, astrocytoma, basal cell carcinoma, brain tumor, bile duct cancer, bladder cancer, bone cancer, breast cancer, bronchial tumor, Burkitt Lymphoma, carcinoma of unknown primary origin, cardiac tumor, cervical cancer, chordoma, chronic lymphocytic leukemia (CLL), chronic myelogenous leukemia (CML), chronic myeloproliferative neoplasm, colon cancer, colorectal cancer, craniopharyngioma, cutaneous T-cell lymphoma, ductal carcinoma, embryonal tumor, endometrial cancer, ependymoma, esophageal cancer, esthesioneuroblastoma, fibrous histiocytoma, Ewing sarcoma, eye cancer, germ cell tumor, gallbladder cancer, gastric cancer, gastrointestinal carcinoid tumor, gastrointestinal stromal tumor, gestational trophoblastic disease, glioma, head and neck cancer, hairy cell leukemia, hepatocellular cancer, histiocytosis, Hodgkin lymphoma, hypopharyngeal cancer, intraocular melanoma, islet cell tumor, Kaposi sarcoma, kidney cancer, Langerhans cell histiocytosis, laryngeal cancer, leukemia, lip and oral cavity cancer, liver cancer, lobular carcinoma in situ, lung cancer, lymphoma, macroglobulinemia, malignant fibrous histiocytoma, melanoma, Merkel cell carcinoma, mesothelioma, metastatic squamous neck cancer with occult primary, midline tract carcinoma involving NUT gene, mouth cancer, multiple endocrine neoplasia syndrome, multiple myeloma, mycosis fungoides, myelodysplastic syndrome, myelodysplastic/myeloproliferative neoplasm, nasal cavity and para-nasal sinus cancer, nasopharyngeal cancer, neuroblastoma, non-Hodgkin lymphoma, non-small cell lung cancer, oropharyngeal cancer, osteosarcoma, ovarian cancer, pancreatic cancer, papillomatosis, paraganglioma, parathyroid cancer, penile cancer, pharyngeal cancer, pheochromocytomas, pituitary tumor, pleuropulmonary blastoma, primary central nervous system lymphoma, prostate cancer, rectal cancer, renal cell cancer, renal pelvis and ureter cancer, retinoblastoma, rhabdoid tumor, salivary gland cancer, Sezary syndrome, skin cancer, small cell lung cancer, small intestine cancer, soft tissue sarcoma, spinal cord tumor, stomach cancer, T-cell lymphoma, teratoid tumor, testicular cancer, throat cancer, thymoma and thymic carcinoma, thyroid cancer, urethral cancer, uterine cancer, vaginal cancer, vulvar cancer, and Wilms&#39; tumor. 
     For example, any of the methods described herein can be used to treat a cancer selected from the group consisting of: glioblastoma, squamous cell carcinoma, breast cancer, colon cancer, hepatocellular cancer, melanoma, neuroblastoma, pancreatic cancer, and prostate cancer. 
     The term “therapeutic agent” refers to a therapeutic treatment that involves administering to a subject a therapeutic agent that is known to be useful in the treatment of a disease, e.g., a cancer, an infection. For example, a cancer therapeutic agent can decrease the size or rate of tumor growth. In other instances, a cancer therapeutic agent can affect the tumor microenvironment. 
     Non-limiting examples of therapeutic agents that can be expressed and/or secreted in any of the bacterial strains described herein include: an inhibitory nucleic acid (e.g., a microRNA (miRNA), a short hairpin RNA (shRNA), a small interfering RNA (siRNA), an antisense), a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin (e.g., a diphtheria toxin, a gelonin toxin, anthrax toxin), an antimicrobial peptide, and an antibody or antigen-binding fragment thereof. 
     In some instances, the therapeutic agent is a therapeutic polypeptide. In some instances, the therapeutic polypeptide includes one or more polypeptides (e.g., 2, 3, 4, 5, or 6). In some instances, the therapeutic polypeptide is conjugated to a toxin, a radioisotope, or a drug via a linker (e.g., a cleavable linker, a non-cleavable linker). 
     In some instances, the therapeutic agent is cytotoxic or cytostatic to a target cell. 
     The phrase “cytotoxic to a target cell” refers to the inducement, directly or indirectly, in the death (e.g., necrosis or apoptosis) of the target cell. For example, a target cell can be a cancer cell (e.g., a cancerous cell or a tumor-associated immune cell (e.g., macrophage) or an infected cell. 
     The phrase “cytostatic to a target cell” refers to direct or indirect decrease in the proliferation (cell division) of a target cell in vivo or in vitro. When a therapeutic agent is cytostatic to a target cell, the therapeutic agent can, e.g., directly or indirectly result in cell cycle arrest of the target cell. In some examples, the therapeutic agent that is cytostatic can reduce the number of target cells in a population of cells that are in S phase (as compared to the number of target cells in a population of cells that are in S phase prior to contact with the therapeutic agent). In some instances, the therapeutic agent that is cytostatic can reduce the percentage of target cells in S phase by at least 20% (e.g., at least 40%, at least 60%, at least 80%) as compared to the percentage of target cells in a population of cells that in S phase prior to contact with the therapeutic agent. 
     Also provided herein are pharmaceutical compositions that include at least three (e.g., 3, 4, 5, 6, 7, 8, 9, or 10) of any of the bacterial strains described herein that express and/or secrete at least one of any of the therapeutic agents described herein. 
     The pharmaceutical compositions can be formulated in any matter known in the art. The pharmaceutical compositions are formulated to be compatible with their intended route of administration (e.g., intravenous, subcutaneous, intraperitoneal, rectal, topical, or oral). In some embodiments, the pharmaceutical composition is administered directly into the site of disease or diseased tissue, e.g., administered into the tumor, administered into the infected tissue. In some embodiments, administering is targeting, e.g., the pharmaceutical composition includes a targeting moiety (e.g., a targeting protein or peptide). 
     In some embodiments, the pharmaceutical compositions can include a pharmaceutically acceptable carrier (e.g., phosphate buffered saline). Pharmaceutical compositions can include any appropriate additional agents, for example, excipients, fillers, disintegrants, lubricants, glidants, binders, solubilizers, bulking agents, buffers, surfactants, chelating agents, adjuvants, and the like, as are known in the art. Single or multiple administrations of formulations can be given depending on for example: the dosage (i.e., number of bacterial cells per mL) and the frequency as required and tolerated by the subject. The dosage, frequency and timing required to effectively treat a subject may be influenced by the age of the subject, the general health of the subject, the severity of the disease, previous treatments, and the presence of comorbidities (e.g., diabetes, cardiovascular disease). The formulation should provide a sufficient quantity of active agent to effectively treat, prevent or ameliorate conditions, diseases or symptoms. Toxicity and therapeutic efficacy of compositions can be determined using conventional procedures in cell cultures, pre-clinical models (e.g., mice, rats, or monkeys), and humans. Data obtained from in vitro assays and pre-clinical studies can be used to formulate the appropriate dosage of any compositions described herein (e.g., pharmaceutical compositions described herein). 
     Efficacy of any of the compositions described herein can be determined using methods known in the art, such as by the observation of the clinical signs of a disease (e.g., tumor size, presence of metastasis). 
     Also provided herein are kits that include at least three of any of the bacterial strains described herein that express and/or secrete at least one of any of the therapeutic agents described herein. In some instances, the kits can include instructions for performing any of the methods described herein. In some embodiments, the kits can include at least one dose of any of the pharmaceutical compositions described herein. The kits described herein are not so limited; other variations will be apparent to one of ordinary skill in the art. 
     EXAMPLES 
     The invention is further described in the following examples, which do not limit the scope of the invention described in the claims. 
     Materials and Methods 
     Strains and Plasmids. 
     Circuit strains were cultured in lysogeny broth (LB) media with 50 μg ml −1  kanamycin and 34 μg ml −1  chloramphenicol for strains containing ColE1 origin and p15A origin plasmids respectively, along with 0.2% glucose, or 50 μg ml −1  spectinomycin for non-lysis colicin strains in a 37° shaking incubator. Exemplary toxins are shown in  FIG. 4  and  FIG. 22 . Exemplary strains are shown in  FIG. 5  and  FIG. 23 . Exemplary plasmids used in this study are described in  FIG. 11  and  FIG. 21 . Colicin E3 and E5 genes were assembled with overlapping PCR of gene blocks (IDT). Colicin V genes were obtained from PCR off of wild-type Colicin V  E. coli  (obtained from Dr. Joe Pogliano and Dr. Roberto Kolter). All plasmids were constructed by Gibson assembly followed by transformation into DH5α (Thermofisher) chemically competent  E. coli . Plasmids were verified by Sanger sequencing before transformation into  E. coli  strain MG1655. 
     For toxin co-culture experiments, wild type MG1655  E. coli  strains were seeded from a −80° glycerol stock into 2 ml LB and incubated in a 37° C. shaking incubator. After cells reached an OD600 between 0.2-0.4, 5 μl culture was added to 200 μl fresh media in a standard Falcon tissue culture 96-well flat bottom plate. Additionally, 5 μl of the purified colicin lysate was added to each well. Cultures were grown at 37° shaking for 19 hours and their optical density at 600 nm absorbance was measured every 5 min with a Tecan Infinite M200 Pro. Fluorescence measurements were taken every 5 min at 485 nm excitation 520 nm emission, 433 nm excitation 475 nm emission, and 590 nm excitation 630 nm emission, for GFP, CFP, and RFP respectively. 
     Microfluidics and Microscopy. 
     The microfluidic devices and experiment preparation protocols used in this study are similar to those reported elsewhere (see, e.g., Prindle, et al. A sensing array of radically coupled genetic biopixels. Nature, 481(7379):39-44, 2012.). All microfluidic experiments were performed in a side-trap array device with bacteria growth chambers approximately 100×80 μm in area and approximately 1.2 μm in height. The appropriate  E. coli  strain was seeded from a −80° glycerol stock into 5 ml LB with the appropriate antibiotics. For lysis strain, 0.2% glucose was added to the media. After growth for 8-12 h at 37° in a shaking incubator, the culture was diluted 100-fold into 25 ml of the same medium in a 50 ml Erlenmeyer flask and grown until reaching an OD between 0.4-0.6 (Plastibrand 1.5 ml cuvettes were used). Once the above OD was reached cells were concentrated by centrifugation at 5,000 g for 1 min and resuspended in 10 μl of LB media with 0.75% Tween-20 and the appropriate antibiotics. This concentrate was used to vacuum-load the cells for single-strain experiments. For multi-strain experiments, cultures were first normalized to the same OD 600  prior to centrifugation and mixed at either 1:1, 1:2, 4:6, or 1:5 ratio for 2 strain experiments, or mixed at a 1:1:1 ratio for 3 strain experiments prior to vacuum loading. The control of media flow into the microfluidic device was gravity driven. Chip temperatures were maintained at 37□ with a plexiglass incubation chamber encompassing the entire microscope. 
     For sequential loading experiments the initial two strains were prepared as described for 2 strain experiments. Subsequent strains were then seeded from a −80° glycerol stock into 5 ml LB with 0.2% glucose and the appropriate antibiotics. After growth for 8-12 h at 37° in a shaking incubator, the culture was diluted 100-fold into 100 ml of the same medium in a 500 ml Erlenmeyer flask and grown until reaching an OD between 0.1-0.4 (Plastibrand 1.5 ml cuvettes were used). Once the above OD was reached cells were concentrated by centrifugation at 5,000 g for 5 min and resuspended in 1 ml of LB media with 0.075% Tween-20 and the appropriate antibiotics. Cells were then loaded into a second or third inlet port of the microfluidic device, and introduced into the traps by flick loading. Flick loading was done by flicking the tygon tubing leading to the inlet of the microfluidic device, in order to disturb the laminar flow within the device to allow cells to be washed into the microfluidic traps. The control of media flow into the microfluidic device was gravity driven. For the duration of the experiment LB media containing 34 μg ml −1  chloramphenicol was used. Chip temperatures were maintained at 37° C. with a plexiglass incubation chamber encompassing the entire microscope. 
     For microscopy a Nikon Eclipse TI epifluorescent microscope with phase-contrast-based imaging was used. Image acquisition was performed with a Photometrics CoolSnap cooled CCD camera and Nikon Elements software. For 10× magnification experiments, phase-contrast images were taken with 50-100 μs exposure times. Fluorescence exposure times were 100 μs at 30% intensity, 300 μs at 30% intensity and 100 μs at 30% intensity for gfp, rfp, and cfp respectively. Images were taken either every 3 minutes or every 6 minutes for the duration of the experiment (1-4 days). For 60× magnification experiments, phase-contrast images were taken with 20-50 μs exposure times. Fluorescence exposure times were 50 μs at 30% intensity, 200 μs at 30% intensity and 50 μs at 30% intensity for gfp, rfp, and cfp respectively. Images were taken either every 3 minutes or every 6 minutes for the duration of the experiment (1-4 days). For sequential loading experiments, imaging was paused for the duration of strain loading. 
     Population Estimates and Growth Rate of RPS Strains. 
     Population estimates for the approximate population fractions in the co-culture mixtures were made in the following way. Fluorescence channel image stacks from the dominant strain were converted to 8-bit in ImageJ (Process&gt;Binary&gt;Make Binary). Z-axis profiles were then taken for the cell incubating region (Image&gt;Stacks Plot Z-axis Profile) and the values were normalized to 1 by dividing by the max value. The max-value of the fluorescence time-series trace for the dominant strain was used as a standard for accumulated fluorescence of a culture with 100% dominant strain alone. Susceptible strain fractions were estimated by subtracting the normalized dominant strain values from 1. The values were then normalized to the initial cell fractions corresponding to roughly 70% dominant strain and 30% susceptible strain. Initial cell fractions were counted manually using the ImageJ cell counter plugin. 
     For growth rate experiments, the appropriate  E. coli  strains were seeded from a −80° glycerol stock into 2 ml LB and the appropriate antibiotics and incubated in a 37° C. shaking incubator. After cells reached an OD 600  of 0.1, 1 ml culture was added to a 125 ml Erlenmeyer flask containing 25 ml fresh media with appropriate antibiotics and left shaking at 270 rpm. Once the samples reached an OD 600  of 0.1 samples were taken every 10 minutes and measured at OD 600  using a DU 740 Life Science Uv/vis spectrophotometer. 
     Passage and Plate Reader Experiments. 
     For passage experiments, the appropriate  E. coli  strains were seeded from a −80° glycerol stock into 2 ml LB with 0.2% glucose with the appropriate antibiotics and incubated in a 37° C. shaking incubator. At an OD 600  of 0.2, 10 μl culture was added to 190 μl fresh media containing appropriate antibiotics in a standard Falcon tissue culture 96-well flat bottom plate. Cells were incubated at 37° shaking in a Tecan Infinite M200 Pro, each passage was grown for 12 hours and the optical density at 600 nm absorbance was measured every 10 min. Fluorescence measurements were taken every 10 min at 485 nm excitation 520 nm emission, 433 nm excitation 475 nm emission, and 590 nm excitation 630 nm emission for GFP, CFP, and RFP respectively. After 12 hours, the OD 600  of each sample was diluted to 0.2 and 10 μl of each sample was passaged into 190 μl of fresh media containing appropriate antibiotics in a new culture plate. For cycling strains, the appropriate  E. coli  strains were grown immediately before the appropriate passage from a −80° glycerol stock, as described before, to an OD 600  of 0.2, and 10 μl of the culture containing the new strain was then added to the appropriate passage before measurements were taken. Samples for Sanger sequencing were collected at the end of each passage. For analysis, a successful lysis event was defined as an OD 600  growth curve that had a defined peak followed by a drop in OD. 
     Plate Reader Fluorescence. 
     For well-plate experiments, the appropriate  E. coli  strains were seeded from a −80° glycerol stock into 2 ml LB with 0.2% g glucose and the appropriate antibiotics and incubated in a 37□ shaking incubator. After cells reached an OD600 between 0.2-0.6, 5 μl culture was added to 200 μl fresh media containing appropriate antibiotics in a standard Falcon tissue culture 96-well flat bottom plate. Cells were incubated at 37° shaking and imaged every 5 min in a Tecan Infinite M200 Pro. Dilutions were grown for 19 hours and their optical density at 600 nm absorbance was measured every 5 min. Fluorescence measurements were taken every 5 min at 485 nm excitation 520 nm emission, 433 nm excitation 475 nm emission, and 590 nm excitation 630 nm emission, for GFP, CFP, and RFP respectively. The resulting curves were used to estimate OD600 of lysis and growth dynamics of each strain. 
     Example 1—Two Strain System 
     The first stage of development consisted of engineering a selective advantage. A strategy to give one strain a selective advantage over the other was initially investigated. 
     A strategy to give one strain a selective advantage over the other was initially investigated. From the range of possible colicins, two (colicin E3, colicin E7) were identified which are lethal through DNase and rRNase activity (see, e.g.,  FIG. 4  and  FIG. 22 ). Toxin effects were verified in microfluidic and plate reader experiments ( FIG. 5 ,  FIG. 6 ). To characterize this effect, a p15A origin plasmid was constructed with a weak constitutive promoter driving colicin and Col E1 lysis protein. In addition, the plasmid included a constitutive promoter driving the immunity protein linked to a fluorescence reporter protein. A second identical constitutive promoter drives a secondary immunity protein (exemplary plasmid diagrams are shown in  FIG. 11  and  FIG. 21 ). Each of the plasmid constructs was expressed in MG1655  E. coli . The initial strains, addressed as “Strain A” and “Strain B”, produce colicin E3+E3 immunity+E7 Immunity+sfGFP, and colicin E7+E7 immunity+mCherry, respectively ( FIG. 1A ). To study the dynamics of our engineered strains, microfluidic devices were used containing rectangular traps of dimension 100 μm×80 μm×1 μm. Strain B, named the ‘disadvantaged strain’, was initially seeded into the microfluidic device and allowed to fully colonize the traps. At this point, Strain A, called the ‘dominant strain’, was introduced into the microfluidic device. Following the introduction of Strain A, an exponential increase of the dominant strain and decay of the disadvantaged strain was observed ( FIG. 1B ). These experiments demonstrate that colicins can be used to control population dynamics. However, a possible outcome of this experiment could be mutation of the ‘disadvantaged strain’ against the dominant strain due to long term exposure to a low concentration of colicin. 
     To address this concern, it was reasoned that synchronized release of colicin would enable the simultaneous release of a more lethal concentration of colicin, while also limiting the exposure time to low concentrations of colicin. To test this hypothesis, p15A origin plasmids were constructed in which the initial col E1 Lysis protein was removed and replaced with the X174 E lysis protein under control of the luxI promoter ( FIG. 1C ). A second plasmid, from a synthetic oscillator reported elsewhere (Danino, et al. A synchronized quorum of genetic clocks. Nature, 463(7279):326-330, 2010), contains luxI and luxR driven by their native bidirectional promoter on the ColE1 origin plasmid (‘activator plasmid’). In addition, a second lux promoter drives the production of a fluorescent reporter protein. In this two plasmid architecture, the lux quorum-sensing system from  Aliivbrio fischeri  was used to create a positive feedback loop driving quorum lysis. In short, LuxI catalyzes the production of the diffusible quorum-sensing molecule N-acyl homoserine lactone (AHL). This molecule binds to the constitutively produced luxR transcription factor, forming a complex which acts as a transcriptional activator of the luxI promoter. It was expected that the different strains would synchronously lyse resulting in simultaneous release of colicin when both populations are at their lowest ( FIG. 1D ). To test this idea,  E. coli  containing both these plasmids were grown in the microfluidic device previously described. The dominant and disadvantaged strains were loaded at a ratio of 1:5 respectively and co-cultured for a duration of 600 minutes. It was observed that both strains lysed synchronously within each chamber and drastically improved strain takeover rate compared to strains lacking synchronized lysis (FIG.  1 E). This synthetic colicin-based circuit demonstrates that, when combined with an engineered selective advantage, lysis mediated population control is a powerful tool for controlling populations. 
     Example 2—Three Strain System 
     During the second stage of development the system was expanded to three-strains. 
     Since a two strain population control system would only enable the switching from one strain to another, the design was expanded to a three strain system that could be cycled in a “rock paper scissors” approach. To explore this, a third toxin was identified, colicin V, which acts by disrupting the membrane potential. Each strain contains the same two plasmid architecture described in  FIG. 1C  but with orthogonal sets of colicins. The three strains, now referred to as strain 1, strain 2 and strain 3, contain colicin E3, colicin E7 and colicin V respectively. In this system, each strain produces a colicin lethal to the preceding strain and two immunity proteins ( FIG. 2A ). The first immunity protein gives the current strain protection to its own colicin production. In addition, a second immunity protein protects the current strain to the toxicity of the colicin produced by the preceding strain. 
     Three  E. coli  strains were engineered in which each strain contains a unique toxin and antitoxin system (TA module). In monoclonal populations, TA modules aid in plasmid stabilization because mutation or loss of the antitoxin results in cell death either due to the presence of extracellular toxin produced by the healthy bacteria or killing of newborn plasmid-free cells through the prolonged persistence of toxin producing mRNA (see, e.g. K. Gerdes,  Nature Biotechnology  6, 1402 (1988)). By expanding the mechanism of the TA module to a multi-strain ecology, each TA module gives its host strain the added ability to kill any other strain that does not have the corresponding antitoxin, enabling external control over displacement of the existing population ( FIG. 12A ). A synthetic “rock, paper, scissors” (RPS) ecology was created by adding a secondary antitoxin into each strain so that each strain can be killed by a subsequent strain in a cycle ( FIG. 12B ). This RPS system can be coupled with any circuit of interest to increase stabilization. In this combined system, a circuit that has mutated in one strain can be replaced by the introduction of a fresh batch of the next RPS housing strain. Thus, rather than attempting to “beat Darwin,” an engineering strategy was developed that enabled external control over the evolution and composition of the ecology. 
     Because multi-strain competition dynamics are typically dictated by differences in growth rate, the dynamics of the three strains were characterized first individually. Growth rates of the three lysis strains and the wild-type MG1655  E. coli  were compared by using fluorescence microplate reader absorbance experiments. Before the lysis event occurred, it was found that the addition of engineered circuits had little effect on the growth compared to the wild-type control. The threshold OD 600  was recorded at which each of the three strains lysis ( FIG. 2B ). 
     Next, the effect of differences in OD 600  of lysis on the period of lysis was explored in the microfluidic devices. The microfluidic device was loaded with each individual strain and imaged every six minutes. The period of lysis between the three strains was found to be relatively uniform in spite of different OD 600  thresholds of lysis ( FIG. 2C ). 
     Without wishing to be bound by theory, it was hypothesized that this may be due to a lower post-lysis survival fraction of Strain 1 cells in comparison to survivor cells belonging to Strain 2 and Strain 3. Phenotypic differences in the lysis dynamics of the three strains were noticed. The lysis event of Strain 1 results in a more explosive lysis event, which leaves a smaller fraction of surviving cells and expels more lysate from the trap. Alternatively, strain 3 has a very mild lysis event resulting in a higher fraction of surviving cells and more cell lysate buildup in the microfluidic trap ( FIG. 7 ). 
     In any environment, once engineered cells have mutated they cannot be reverted back to the non-mutated state. They must be removed and replaced by healthy cells. Such a ‘system reboot’ interrupts dynamic circuit function in the environment. A multi-strain RPS ecology should in theory enable the removal of mutated, or mutation prone, cells without interrupting the dynamics of the circuit of interest. After validating the expanded function of the TA module in a RPS system, the utility of the stabilizing RPS elements with a genetic circuit that is subject to high selective pressure was tested. The quorum driven synchronized lysis circuit (SLC) was chosen, which has been investigated for microbial therapeutics such as drug delivery to tumors in vivo (see, e.g., M. O. Din, et al.,  Nature  536, 81 (2016); T. Danino, O. Mondragón-Palomino, L. Tsimring, J. Hasty, Nature 463, 326 (2010)). With the SLC circuit, a quorum sensing molecule (AHL), gradually accumulates in the growth environment in proportion to population density. When the population reaches a threshold density, synchronized lysis eliminates around 90% of the bacteria, leaving about 10% to reseed population growth. The resulting dynamics of the cell population are cycles of cell growth and synchronized lysis. However, when employed in in vivo environments where selective media cannot be used, plasmid loss or mutations are expected to result in loss of function over long time periods. 
     It was investigated whether successful plasmid stabilization from the RPS system would result in strain takeover without any interruption of the oscillatory dynamics ( FIG. 13A ). The SLC and TA modules were integrated into a two-plasmid system with one plasmid containing the lysis gene, E, from the phage ϕX174 (X174E), a TA module, immunity proteins, and an activator-reporter plasmid ( FIG. 13B ). To investigate how the different dynamics of the strains would impact the interactions between them, each of the strain pairs were tested in microfluidic devices. Due to the difference in lysis threshold, it was expected that strain 1 would lyse before strain 2 and strain 3, causing a problem in strain takeover. A three strain RPS system was developed in which each strain contained a distinct toxin-antitoxin pair as well as a secondary antitoxin to one other strain ( FIG. 12C ). To achieve this, used colicins were used, which are naturally occurring toxin-antitoxin systems that are lethal to certain  E. coli  strains and are effective antagonistic agents within  E. coli  populations in vivo ( FIG. 16A-D ) (see, e.g., B. C. Kirkup, M. A. Riley,  Nature  428, 412 (2004), A. E. Boyer, P. C. Tai,  Journal of bacteriology  180, 1662 (1998); E. Cascales, et al.,  Microbiology and molecular biology reviews  71, 158 (2007); M. M. Zambrano, D. A. Siegele, M. Almiron, A. Tormo, R. Kolter,  Science  259, 1757 (1993)). 
     To test this, each strain pair was co-cultured in the microfluidic device at an initial seeding ratio of 1:5 advantaged to susceptible. Each of the three strains were monitored via fluorescence reporter proteins sfGFP, CFP and mKate2. Production of the fluorescent reporter is driven by the luxI promoter. Strain 3 contains a plasmid producing colicin E7 and E7 immunity protein, and a colicin V immunity protein. Strain 2 contains a plasmid producing colicin E3 and E3 immunity protein, and an E7 immunity protein. Strain 1 contains a plasmid producing colicin V and V immunity protein and an E3 immunity protein. Thus, each pair of strains has one ‘dominant strain’, immune to the toxin produced by the other strain, and a ‘susceptible’ strain, vulnerable to the toxin produced by the other. Therefore, the reporter protein is only produced after initiation of the AHL quorum based positive feedback loop. 
     Since displacement within microbial co-cultures are typically dominated by differences in growth rate, growth rate of each RPS strain was measured ( FIG. 12D ). The efficacy of the engineered colicin kill circuits in microfluidic devices by co-culturing the strain pairs at a 1:2 ratio of dominant to susceptible was also determined. In each case, it was observed that a rapid increase of the dominant strain and decay of the susceptible strain, confirming that the colicin produced by the dominant strain was effective against the susceptible strain, but not vice versa ( FIG. 12E, 12F ). 
     Using this architecture, three strains were created that exhibited simultaneous cycles of synchronized lysis and constant RPS competition ( FIG. 13C ). Each RPS lysis strain was characterized individually ( FIGS. 17A-D ), and each strain pair was validated in microfluidic devices with initial seeding ratios of both 1:1, and 1:5, dominant to susceptible. It was observed that in addition to successful strain displacement, the function of the synchronized lysis circuit remained unaffected, as all strains lysed synchronously within each chamber. At 1:1 dominant to susceptible, take-over occurred in 100% of cultures (n=35) for each strain pair and a single lysis event was sufficient to complete strain take-over ( FIG. 18A ). For the three pairings at a 1:5 ratio (strain 1 and 3, 3 and 2, 2 and 1) dominant strain take-over occurred in 100%, 100%, and 92% of the cultures (n=396), respectively ( FIG. 2D ,  FIG. 18B ). For co-cultures consisting of strain 1 and strain 2, a small fraction (&lt;8%) of strain 2 was able to out-compete strain 1 to colonize the trap. In all cases, the function of the SLC circuit was not interrupted during strain changeovers ( FIG. 13D-13F ). 
     Without wishing to be bound by theory, it was hypothesized that this may be caused by the lower lysis threshold which characterizes strain 1. Strain 1 began lysis prior to strain 2. As a result, the released colicin has a lower relative concentration to target strain 2. Additionally, while the two strains were initially loaded at a ratio of 1:5 dominant to disadvantaged, in most cases the observed ratio at the time of the first lysis event was different. 
     To investigate this further, a microfluidic experiment was conducted in which both strains were loaded at an equal ratio 1:1. In the majority of cases, before the occurrence of the first lysis event the dominant strain had already completely taken over the microfluidic trap. In a few cases, the traps still had both strains present. However, the dominant strain had a larger population size, leading to a single lysis event being sufficient for trap takeover (see, e.g.,  FIG. 2E-2G ,  FIG. 13D-13F ). 
     Microscopy at single cell resolution (60× magnification) visually confirmed that the disadvantaged cells started dying prior to synchronized lysis. Without wishing to be bound by theory, this may suggest that there is some level of ‘leaky expression’ of lysis protein which leads to the release of a small amount of colicin during exponential growth phase. 
     Example 3—Population Dynamics 
     Although co-culture of dominant-susceptible strain pairs enabled consistent strain displacement, an ecology consisting of three antagonistic strains may introduce novel emergent properties when cultured simultaneously. A mathematical model was developed that described the switching population dynamics and reduced it to a discrete-time map that permitted analytical predictions for the switching frequency and interval duration (See Example 5). It was found that when all three strains were present simultaneously, cycles of population dominance between the three strains was an emergent property of the system. Under the assumption that the system was closed to the introduction of fresh cells, the strain that initially started at a higher concentration subsequently dominated the trap ( FIG. 19 ). Alternatively, given a small constant supply of each strain, the trajectory of the three-strain system converged to a stable limit cycle regardless of the initial ratios between the three strains ( FIG. 3E ,  FIG. 13G ). 
     To test this emergent property, all three strains were simultaneously loaded into a single microfluidic device. The same experimental setup described above was used to test the theoretical robustness of the system. The only difference in the protocol consisted in applying a high flow rate following the cell loading in the microfluidic device. This procedure was meant to flush the majority of the cells out of the traps, leaving only roughly 1 to 10 cells in each trap. Using this method, a wide range of relative ratios between the three strains in the various traps were obtained, allowing testing a large distribution of initial concentrations. 
     Four separate microfluidic experiments totaling 1582 individual microfluidic traps were analyzed. Three different dynamics were observed. Four separate microfluidic experiments were analyzed, totaling 1582 individual microfluidic culture regions and it was observed that the system exhibited cyclical behavior between the three strains such as strain 2 to strain 1 to strain 3 ( FIG. 20A-20B ). The dynamics for ˜75% of the traps consisted of a single strain out-competing the others before the first lysis event occurred. The single strain dominated the trap for the duration of the experiment. In the second case (˜20%) traps cycled between two strains, for example strain 1 to strain 2. In the third case (˜5%) of traps cycled through three strains, for example strain 1 to strain 2 to strain 3. By aggregating all transition events from the four experiments it is observed that the experimental results align well with the theoretical trajectories ( FIG. 3F ). As predicted by the model, the three strains competed until two were eliminated and a single strain survived ( FIG. 3F ,  FIG. 13H ). 
     Under ideal experimental conditions, a constant supply of the next strain was provided in the cycle. However, due to experimental constraints, strain cycling was dependent on cells being washed into the trap from the upstream traps and channel. It was demonstrated that under variable conditions containing all 3 strains and all 3 colicins, strains cycle sequentially. However, due to trap geometry, as duration of the experiment increases, the buildup of cell lysates within the microfluidic traps prevents new cells from being washed in upstream, reducing the ability for strain cycling to continue. Due to the limitations of these microfluidic experiments, a full cycle of the system in a single run cannot be shown. However, several instances were shown where the strains cycle from Strain 2 to Strain 1 then Strain 3 as well as other scenarios ( FIG. 3D-3E ,  FIG. 13G ). Nevertheless, by aggregating the data of four experiments and 1,600 microfluidic traps, it was demonstrated that variations of the initial conditions of the system (i.e., what the concentrations of each strain begin at initially) do not prevent oscillations between the three-strain system from reaching stability, cycling through the strains one at a time, sequentially ( FIG. 3C ,  FIG. 19A-19B ,  FIG. 9 ). This demonstrates the robustness of the system in that variations in the initial conditions would not perturb the steady state of the system. For in-vivo applications this means that achieving the desired strain cycling will not be too sensitive to the initial conditions (e.g., concentration of dosing, time of dosing, etc.). 
     The consistent convergence of the RPS ecology to the expected behavior supports the feasibility of engineering ecologies to exhibit predictable and precise dynamics. The potential for synthetic microbial communities to enable new biotechnological applications has long been known (see, e.g., B. Kerr, M. A. Riley, M. W. Feldman, B. J. Bohannan,  Nature  418, 171 (2002); L. R. Lynd, et al.,  Nature biotechnology  26, 169 (2008); T. Großkopf, O. S. Soyer,  Current opinion in microbiology  18, 72 (2014); K. Zhou, K. Qiao, S. Edgar, G. Stephanopoulos,  Nature biotechnology  33, 377 (2015)). Engineered ecologies exhibit complex functions that can be difficult to engineer into single populations (see, e.g., J. Shong, M. R. J. Diaz, C. H. Collins,  Current Opinion in Biotechnology  23, 798 (2012); K. Brenner, L. You, F. H. Arnold,  Trends in biotechnology  26, 483 (2008)). 
     Example 4—Plasmid Stability 
     A RPS synthetic ecology strategy allows external control over the evolution and composition of the ecology, enabling displacement of undesired strains through manual input without interrupting circuit function. In order to demonstrate this concept and prolong the functional stability of the SLC using the RPS system, dynamic expression in the absence of the selective antibiotic (kanamycin) was attempted. In this case, selective pressure against the SLC activator plasmid should result in rapid loss of function. 
     Two scenarios ( FIG. 14A ) were investigated. In scenario 1, each strain was cultured individually in LB medium lacking kanamycin. In the absence of selective antibiotic, loss of circuit function was universal and resulted in the loss of fluorescence expression and synchronized lysis dynamics. The elapsed time before synchronized lysis was lost (n=16) was recorded, and it was found that between 80 to 90% of plasmid loss occurred within 32 hours, after which the strains grew uncontrollably ( FIG. 14B, 14C , where L.O.F. stands for “loss of function”). In scenario 2, the experiment was started with a co-culture of strain 2 and strain 1, allowing strain 1 to take over the trap. After 12 hours, strain 3 was added to displace strain 1, and at 30 hours strain 2 was re-introduced to displace strain 3. Therefore, starting with strain 2, a full cycle was completed in a way that would likely be maintained over an indefinite period. By manually adding subsequent strains before the previous strain mutated, the duration of circuit stability was able to be prolonged without interrupting circuit function ( FIG. 14D ). 
     To further explore the effect of the RPS system on a mutable genetic circuit a batch passage experiment was conducted to compare two scenarios ( FIG. 15A ). In the first scenario, culture medium containing antibiotics was inoculated with Strain 1 and passaged the culture into fresh growth medium every 12 hours. In scenario 2, a culture was also inoculated with Strain 1 and passaged every 12 hours, however every 3 passages, the next strain in the RPS cycle was also added. It was observed that in scenario 1, mutations began at passage 4 and once the loss of synchronized lysis occurred, it was never recovered. However, in scenario 2 it was observed that a delay in the loss of synchronized lysis as well as recovery of lysis function even after it had been lost in previous passages ( FIG. 15B ). Sanger sequencing of a 1-kilobase pair region containing the X174E lysis gene and Lux cassette revealed that the RPS strategy reduced the occurrence of mutations over the same duration. In this way, by shifting the challenge of eliminating individual mutated cells to the elimination of an entire population, it was demonstrated the ability of the RPS system to prevent loss of function of a circuit, whether by mutation or plasmid loss. 
     As an expandable and modular platform to ensure genetic stability, the RPS system provides an additional layer of control allowing it to be combined with other traditional strategies to maintain plasmid stability. This approach may enable synthetic biologists to engineer systems that can be maintained long-term in the absence of selective antibiotics, impacting applications ranging from therapeutics to bioremediation, production, and sensing technologies. These applications will require the development of new RPS strains that are armed with different natural or synthetic toxin-antitoxin systems due to the prevalence of colicin resistance that can appear relatively quickly depending on environmental conditions. In a broader scope, the use of an engineered “synthetic ecology” to control the stability of genetic constructs creates possibilities for applied dynamical synthetic ecosystems through the programmed manipulation and interaction of individual sub-populations. 
     Example 3—Models 
     These observations were integrated into a computational model to visually show how this three-strain lysis-based system may behave with respect to a wide range of parameters. Under the assumptions that each strain could be completely killed by the other, it was found that each of the three strains would cycle once, and the strain that started initially at a higher concentration would dominate the trap ( FIG. 3A ). All three strains were simultaneously loaded into a single microfluidic device. All three strains were cultured to the same approximate OD then mixed together. The mixture of cells was then loaded into the microfluidic device. The system was able to cycle through the three strains, for example strain 2 to strain 1 to strain 3 ( FIG. 3B-C ). No instance was observed where the strains cycled back to the first strain to complete a full cycle. Due to the lethal effects of one strain on another, the three strains could compete until a single champion remained. 
     It was hypothesized that to achieve persistent switching in the model, adding a small (epsilon) representing a constant seed of cells is useful to avoid complete elimination of either strain ( FIG. 3D ). This c term represents the continuous addition of the next strain in the system to provide a constant supply of each cell type. Furthermore, the trajectory of the three-strain system converges to a stable limit cycle which is robust with respect to a wide range of initial conditions and system parameters ( FIG. 8 ). 
     Three bacterial strains are considered with densities p, q, r that in the absence of colicins grow exponentially with the same nominal growth rate which can be scaled out without loss of generality. These three strains produce three types of colicins. The concentrations of these colicins in extracellular media are C p , C q , C r , respectively. The role of these colicins is that they slow down the growth of each other in a circular manner: C p  slows down the growth of q, so it grows with rate (1+C p ) −1 , C q  similarly slows down r, and C r  slows down p. Furthermore, all strains produce quorum-sensing molecules AHL, and the extracellular concentration of AHL is denoted A. The colicins that cells produce remain conned to the respective cells and do not affect other strains until released into the extracellular media during lysis events. The lysis of all strains occurs if A is greater than or equal to A c  during which most cells get lysed, but a small fraction δ survives. The AHL in extracellular space is constantly diluted with rate γ A , while colicins are diluted with the rate γ C . 
     Suppose that at time t i  right after lysis event i, the values of all 7 concentrations are p i , q i , r 1 , C p   i , C r   i , C q   i , A i , respectively. Note that by assumption A i =A c  (the lysis event is short, and the concentration of AHL does not have a chance to change). The subsequent evolution of these dynamical variables is governed by the following equations: 
     
       
         
           
             
               
                 
                   
                     p 
                     . 
                   
                   = 
                   
                     p 
                     
                       1 
                       + 
                       
                         C 
                         r 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     q 
                     . 
                   
                   = 
                   
                     q 
                     
                       1 
                       + 
                       
                         C 
                         p 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     r 
                     . 
                   
                   = 
                   
                     r 
                     
                       1 
                       + 
                       
                         C 
                         q 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       C 
                       . 
                     
                     p 
                   
                   = 
                   
                     
                       γ 
                       C 
                     
                      
                     
                       C 
                       p 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       C 
                       . 
                     
                     q 
                   
                   = 
                   
                     
                       - 
                       
                         γ 
                         C 
                       
                     
                      
                     
                       C 
                       q 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       C 
                       . 
                     
                     r 
                   
                   = 
                   
                     
                       γ 
                       C 
                     
                      
                     
                       C 
                       r 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
             
               
                 
                   A 
                   = 
                   
                     
                       α 
                        
                       
                         ( 
                         
                           p 
                           + 
                           q 
                           + 
                           r 
                         
                         ) 
                       
                     
                     - 
                     
                       
                         γ 
                         A 
                       
                        
                       A 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     After the lysis event i, the concentrations of p, q, r are small, and the concentration of AHL initially goes down due to dilution. But as the total bacterial density p+q+i grows sufficiently large, the concentration of AHL begins to grow back. When A reaches A c  again at time t i+1 , new lysis event occurs. At this moment, the concentrations of the three strains that were equal to P i+1 , Q i+1 , R i+1 , respectively, are instantly reduced by the fraction δ, 
       | p   i+1   =δP   i+1 +ϵ  (8)
 
         q   i+1   =δQ   i+1 +ϵ  (9)
 
         r   i+1   =δR   i+1 +ϵ  (10)
 
     [NOTE: a small ε was added to avoid complete elimination of either strain. Seemingly minor, but crucial, persistent switching does not seem to occur without it]. At the same time, colicins are released from the lysed cells into the extracellular space and added to the colicins that were there before: 
         C   p   i+1   =C   p ( t   i+1   − )+β(1−δ) P   i+1   (11)
 
         C   q   i+1   =C   q ( t   i+1   − )+β(1−δ) Q   i+1   (12)
 
         C   r   i+1   =C   r ( t   i+1   − )+β(1−δ) R   i+1   (13)
 
     Here P i+1 =p(t i+1   − ) is the density of strain p immediately before the i+1-st lysis event, and similarly for Q and R. Parameter β characterizes the release rate of colicins by bacteria during lysis (assumed to be the same for all three strains). 
     Simulations of Eqs. (1)-(13) show robust switching dynamics of dominant stain densities in a broad range of parameter values ( FIGS. 24A, 24B, 25A, 25B, 26A, and 26B ). 
     Analytics. 
     Equations for colicin dynamics between lysis events are linear, so they can be trivially integrated, 
         C   p,q,r ( t )= C   p,q,r   i   e   −γ     c     (t-t     i     )   (14)
 
     Now, since the colicin concentrations as functions of time are known, equations for the strain concentrations can be integrated: 
     
       
         
           
             
               
                 
                   
                     p 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         p 
                         i 
                       
                        
                       
                         exp 
                          
                         
                           [ 
                           
                             
                               ∫ 
                               
                                 t 
                                 1 
                               
                               t 
                             
                              
                             
                               
                                 dt 
                                 ′ 
                               
                               
                                 1 
                                 + 
                                 
                                   
                                     C 
                                     r 
                                     i 
                                   
                                    
                                   
                                     e 
                                     
                                       - 
                                       
                                         
                                           γ 
                                           c 
                                         
                                          
                                         
                                           ( 
                                           
                                             
                                               t 
                                               ′ 
                                             
                                             - 
                                             
                                               t 
                                               i 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                     
                     = 
                     
                       
                         
                           p 
                           i 
                         
                          
                         
                           exp 
                            
                           
                             [ 
                             
                               
                                 γ 
                                 c 
                                 
                                   - 
                                   1 
                                 
                               
                                
                               log 
                                
                               
                                 
                                   
                                     C 
                                     r 
                                     i 
                                   
                                   + 
                                   
                                     e 
                                     
                                       
                                         γ 
                                         c 
                                       
                                        
                                       
                                         ( 
                                         
                                           t 
                                           - 
                                           
                                             t 
                                             i 
                                           
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     C 
                                     r 
                                     i 
                                   
                                   + 
                                   1 
                                 
                               
                             
                             ] 
                           
                         
                       
                       = 
                       
                         
                           
                             p 
                             i 
                           
                            
                           
                             [ 
                             
                               
                                 
                                   C 
                                   r 
                                   i 
                                 
                                 + 
                                 
                                   e 
                                   
                                     
                                       γ 
                                       c 
                                     
                                      
                                     
                                       ( 
                                       
                                         t 
                                         - 
                                         
                                           t 
                                           i 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   C 
                                   r 
                                   i 
                                 
                                 + 
                                 1 
                               
                             
                             ] 
                           
                         
                         
                           1 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
             
               
                 
                   
                     q 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         q 
                         i 
                       
                        
                       
                         exp 
                          
                         
                           [ 
                           
                             
                               ∫ 
                               
                                 t 
                                 1 
                               
                               t 
                             
                              
                             
                               
                                 dt 
                                 ′ 
                               
                               
                                 1 
                                 + 
                                 
                                   
                                     C 
                                     p 
                                     i 
                                   
                                    
                                   
                                     e 
                                     
                                       - 
                                       
                                         
                                           γ 
                                           c 
                                         
                                          
                                         
                                           ( 
                                           
                                             
                                               t 
                                               ′ 
                                             
                                             - 
                                             
                                               t 
                                               i 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                     
                     = 
                     
                       
                         
                           q 
                           i 
                         
                          
                         
                           exp 
                            
                           
                             [ 
                             
                               
                                 γ 
                                 c 
                                 
                                   - 
                                   1 
                                 
                               
                                
                               log 
                                
                               
                                 
                                   
                                     C 
                                     p 
                                     i 
                                   
                                   + 
                                   
                                     e 
                                     
                                       
                                         γ 
                                         c 
                                       
                                        
                                       
                                         ( 
                                         
                                           t 
                                           - 
                                           
                                             t 
                                             i 
                                           
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     C 
                                     p 
                                     i 
                                   
                                   + 
                                   1 
                                 
                               
                             
                             ] 
                           
                         
                       
                       = 
                       
                         
                           
                             q 
                             i 
                           
                            
                           
                             [ 
                             
                               
                                 
                                   C 
                                   p 
                                   i 
                                 
                                 + 
                                 
                                   e 
                                   
                                     
                                       γ 
                                       c 
                                     
                                      
                                     
                                       ( 
                                       
                                         t 
                                         - 
                                         
                                           t 
                                           i 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   C 
                                   p 
                                   i 
                                 
                                 + 
                                 1 
                               
                             
                             ] 
                           
                         
                         
                           1 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
             
               
                 
                   
                     r 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         r 
                         i 
                       
                        
                       
                         exp 
                          
                         
                           [ 
                           
                             
                               ∫ 
                               
                                 t 
                                 1 
                               
                               t 
                             
                              
                             
                               
                                 dt 
                                 ′ 
                               
                               
                                 1 
                                 + 
                                 
                                   
                                     C 
                                     q 
                                     i 
                                   
                                    
                                   
                                     e 
                                     
                                       - 
                                       
                                         
                                           γ 
                                           c 
                                         
                                          
                                         
                                           ( 
                                           
                                             
                                               t 
                                               ′ 
                                             
                                             - 
                                             
                                               t 
                                               i 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                     
                     = 
                     
                       
                         
                           r 
                           i 
                         
                          
                         
                           exp 
                            
                           
                             [ 
                             
                               
                                 γ 
                                 c 
                                 
                                   - 
                                   1 
                                 
                               
                                
                               log 
                                
                               
                                 
                                   
                                     C 
                                     q 
                                     i 
                                   
                                   + 
                                   
                                     e 
                                     
                                       
                                         γ 
                                         c 
                                       
                                        
                                       
                                         ( 
                                         
                                           t 
                                           - 
                                           
                                             t 
                                             i 
                                           
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     C 
                                     q 
                                     i 
                                   
                                   + 
                                   1 
                                 
                               
                             
                             ] 
                           
                         
                       
                       = 
                       
                         
                           
                             r 
                             i 
                           
                            
                           
                             [ 
                             
                               
                                 
                                   C 
                                   q 
                                   i 
                                 
                                 + 
                                 
                                   e 
                                   
                                     
                                       γ 
                                       c 
                                     
                                      
                                     
                                       ( 
                                       
                                         t 
                                         - 
                                         
                                           t 
                                           i 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   C 
                                   q 
                                   i 
                                 
                                 + 
                                 1 
                               
                             
                             ] 
                           
                         
                         
                           1 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
           
         
       
     
     Finally, the concentration of AHL between lysis events was computed as 
         A ( t )= e   −γ     A     (t-t     i     ) [ A ( t   i )+α∫ t     i     t ( p+q+r ) e   γ     A     t′   dt ′]  (18)
 
     The time of the next lysis event is found from the transcendental equation 
         A   c   =e   −γ     A     (t     i+1     -t     i     ) [ A   c +α∫ t     i     t     i+1   ( p+q+r ) e   γ     A     t′   dt ′]  (19)
 
       or 
       α∫ t     i     t     i+1   ( p+q+r ) e   γ     A     t′   dt′=A   c [ e   γ     A     (t     i+1     -t     i     ) −1]  (20)
 
     From here on it was assumed that the dynamics of AHL is much faster than population dynamics (i.e. γ A &gt;&gt;1). Then AHL concentration tracks the total amount of cells in the chamber, and the expression for A can be simplified, 
         A ( t )=αγ A   −1 [ p ( t )+ q ( t )+ r ( t )]  (21)
 
     so the condition for the next lysis event becomes 
         P   i   +Q   i   +R   i =γ A   A   c α −1   (22)
 
     If colicins also degrade sufficiently fast, so they have time to degrade to negligibly small values by the end of each lysis cycle, as in examples shown in  FIGS. 25A, 25B, 26A, and 26B , then the values of C p   i , C q   i , C r   i , don&#39;t depend on the colicin concentrations during the previous lysis cycle, and are directly proportional to P i , Q i , R i , according to Eqs. (23)-(25): 
         C   p   i =β(1−δ) P   i   (23)
 
         C   q   i =β(1−δ) Q   i   (24)
 
         C   r   i =β(1−δ) R   i   (25)
 
     Substituting these expressions and (8)-(10) in Eqs.(15)-(17) at the time of the next lysis event, t=t i +1 the following implicit mapping is achieved 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 P 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           ) 
                         
                          
                         
                           [ 
                           
                             1 
                             + 
                             
                               
                                 
                                   e 
                                   
                                     
                                       γ 
                                       c 
                                     
                                      
                                     
                                       T 
                                       i 
                                     
                                   
                                 
                                 - 
                                 1 
                               
                               
                                 1 
                                 + 
                                 
                                   
                                     β 
                                      
                                     
                                       ( 
                                       
                                         1 
                                         - 
                                         δ 
                                       
                                       ) 
                                     
                                   
                                    
                                   
                                     R 
                                     i 
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                       
                         1 
                         / 
                         
                           γ 
                           c 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   26 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       Q 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 Q 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           ) 
                         
                          
                         
                           [ 
                           
                             1 
                             + 
                             
                               
                                 
                                   e 
                                   
                                     
                                       γ 
                                       c 
                                     
                                      
                                     
                                       T 
                                       i 
                                     
                                   
                                 
                                 - 
                                 1 
                               
                               
                                 1 
                                 + 
                                 
                                   
                                     β 
                                      
                                     
                                       ( 
                                       
                                         1 
                                         - 
                                         δ 
                                       
                                       ) 
                                     
                                   
                                    
                                   
                                     P 
                                     i 
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                       
                         1 
                         / 
                         
                           γ 
                           c 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   27 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       R 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 R 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           ) 
                         
                          
                         
                           [ 
                           
                             1 
                             + 
                             
                               
                                 
                                   e 
                                   
                                     
                                       γ 
                                       c 
                                     
                                      
                                     
                                       T 
                                       i 
                                     
                                   
                                 
                                 - 
                                 1 
                               
                               
                                 1 
                                 + 
                                 
                                   
                                     β 
                                      
                                     
                                       ( 
                                       
                                         1 
                                         - 
                                         δ 
                                       
                                       ) 
                                     
                                   
                                    
                                   
                                     Q 
                                     i 
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                       
                         1 
                         / 
                         
                           γ 
                           c 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   28 
                   ) 
                 
               
             
           
         
       
     
     where the notation Ti=t i+1 −t i  is introduced for the time interval between ith and (i+1)-st lysis events. The mapping is still implicit because the value T i  is still undetermined. If δ&lt;&lt; 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 P 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           ) 
                         
                          
                         
                           e 
                           
                             T 
                             i 
                           
                         
                       
                       
                         
                           ( 
                           
                             1 
                             - 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 R 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   29 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       Q 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 Q 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           ) 
                         
                          
                         
                           e 
                           
                             T 
                             i 
                           
                         
                       
                       
                         
                           ( 
                           
                             1 
                             - 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 P 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   30 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       R 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 R 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           ) 
                         
                          
                         
                           e 
                           
                             T 
                             i 
                           
                         
                       
                       
                         
                           ( 
                           
                             1 
                             - 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 Q 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   31 
                   ) 
                 
               
             
           
         
       
     
     1, i.e. the density of cells increases significantly between the lysis events, one can simplify expressions in the square brackets by dropping 1&#39;s: 
     Now T i  can be computed by summing up these tree equations and using Eq. (22): 
     
       
         
           
             
               
                 
                   
                     
                       e 
                       
                         T 
                         i 
                       
                     
                      
                     
                       [ 
                       
                         
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 P 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   
                                     R 
                                     i 
                                   
                                 
                               
                               ) 
                             
                             
                               1 
                               / 
                               
                                 γ 
                                 c 
                               
                             
                           
                         
                         + 
                         
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 Q 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     i 
                                   
                                 
                               
                               ) 
                             
                             
                               1 
                               / 
                               
                                 γ 
                                 c 
                               
                             
                           
                         
                         + 
                         
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 R 
                                 i 
                               
                             
                             + 
                             ϵ 
                           
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   
                                     Q 
                                     i 
                                   
                                 
                               
                               ) 
                             
                             
                               1 
                               / 
                               
                                 γ 
                                 c 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                   = 
                   
                     
                       γ 
                       A 
                     
                      
                     
                       A 
                       c 
                     
                      
                     
                       α 
                       
                         - 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   32 
                   ) 
                 
               
             
           
         
       
     
     In the end, the following explicit 3-dimensional mapping for P i , Q i , R i  is achieved: 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           γ 
                           A 
                         
                          
                         
                           A 
                           c 
                         
                          
                         
                           α 
                           
                             - 
                             1 
                           
                         
                          
                         
                           X 
                           i 
                         
                       
                       
                         
                           X 
                           i 
                         
                         + 
                         
                           Y 
                           i 
                         
                         + 
                         
                           Z 
                           i 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   33 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       Q 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           γ 
                           A 
                         
                          
                         
                           A 
                           c 
                         
                          
                         
                           α 
                           
                             - 
                             1 
                           
                         
                          
                         
                           Y 
                           i 
                         
                       
                       
                         
                           X 
                           i 
                         
                         + 
                         
                           Y 
                           i 
                         
                         + 
                         
                           Z 
                           i 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   34 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       R 
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           γ 
                           A 
                         
                          
                         
                           A 
                           c 
                         
                          
                         
                           α 
                           
                             - 
                             1 
                           
                         
                          
                         
                           Z 
                           i 
                         
                       
                       
                         
                           X 
                           i 
                         
                         + 
                         
                           Y 
                           i 
                         
                         + 
                         
                           Z 
                           i 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   35 
                   ) 
                 
               
             
             
               
                 
                     
                 
               
               
                 
                   ( 
                   36 
                   ) 
                 
               
             
             
               
                 where 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       X 
                       i 
                     
                     = 
                     
                       
                         
                           δ 
                            
                           
                               
                           
                            
                           
                             P 
                             i 
                           
                         
                         + 
                         ϵ 
                       
                       
                         
                           ( 
                           
                             1 
                             + 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 R 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   37 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       Y 
                       i 
                     
                     = 
                     
                       
                         
                           δ 
                            
                           
                               
                           
                            
                           
                             P 
                             i 
                           
                         
                         + 
                         ϵ 
                       
                       
                         
                           ( 
                           
                             1 
                             + 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 P 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   38 
                   ) 
                 
               
             
             
               
                 
                   
                     Z 
                     i 
                   
                   = 
                   
                     
                       
                         
                           δ 
                            
                           
                               
                           
                            
                           
                             P 
                             i 
                           
                         
                         + 
                         ϵ 
                       
                       
                         
                           ( 
                           
                             1 
                             + 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 Q 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   39 
                   ) 
                 
               
             
           
         
       
     
     The interval between the lysis events, from Eq. (32), is given by 
     
       
         
           
             
               
                 
                   
                     T 
                     i 
                   
                   = 
                   
                     
                       log 
                        
                       
                         [ 
                         
                           
                             γ 
                              
                             
                                 
                             
                              
                             
                               A 
                               c 
                             
                              
                             
                               α 
                               
                                 - 
                                 1 
                               
                             
                           
                           
                             
                               X 
                               i 
                             
                             + 
                             
                               Y 
                               i 
                             
                             + 
                             
                               Z 
                               i 
                             
                           
                         
                         ] 
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   40 
                   ) 
                 
               
             
           
         
       
     
     Fixed Point and Hopf Bifurcation. 
     The fixed point of the mapping (33)-(33) in which all three strains are equal, P i =Q i =R i =P 0 =γ A A c /3α is considered. In this regime, the period between lysis events is given by 
     
       
         
           
             
               
                 
                   
                     T 
                     
                       f 
                       P 
                     
                   
                   = 
                   
                     
                       log 
                        
                       
                         [ 
                         
                           
                             
                               γ 
                               A 
                             
                              
                             
                               A 
                               c 
                             
                              
                             
                               
                                 
                                   α 
                                   
                                     - 
                                     1 
                                   
                                 
                                  
                                 
                                   ( 
                                   
                                     1 
                                     + 
                                     
                                       β 
                                        
                                       
                                           
                                       
                                        
                                       
                                         P 
                                         0 
                                       
                                     
                                   
                                   ) 
                                 
                               
                               
                                 1 
                                 / 
                                 
                                   γ 
                                   c 
                                 
                               
                             
                           
                           
                             3 
                              
                             
                               ( 
                               
                                 
                                   δ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     0 
                                   
                                 
                                 + 
                                 ϵ 
                               
                               ) 
                             
                           
                         
                         ] 
                       
                     
                     = 
                     
                       
                         log 
                          
                         
                           [ 
                           
                             
                               
                                 γ 
                                 A 
                               
                                
                               
                                 A 
                                 c 
                               
                                
                               
                                 
                                   
                                     α 
                                     
                                       - 
                                       1 
                                     
                                   
                                    
                                   
                                     ( 
                                     
                                       1 
                                       + 
                                       
                                         
                                           βγ 
                                           A 
                                         
                                          
                                         
                                           
                                             A 
                                             c 
                                           
                                           / 
                                           3 
                                         
                                          
                                         α 
                                       
                                     
                                     ) 
                                   
                                 
                                 
                                   1 
                                   / 
                                   
                                     γ 
                                     c 
                                   
                                 
                               
                             
                             
                               
                                 
                                   δγ 
                                   A 
                                 
                                  
                                 
                                   
                                     A 
                                     c 
                                   
                                   / 
                                   α 
                                 
                               
                               + 
                               
                                 3 
                                  
                                 ϵ 
                               
                             
                           
                           ] 
                         
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   41 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           P 
                           ~ 
                         
                         
                           i 
                           + 
                           1 
                         
                       
                       = 
                       
                         
                           
                             P 
                             0 
                           
                            
                           
                             ( 
                             
                               
                                 2 
                                  
                                 
                                   x 
                                   i 
                                 
                               
                               - 
                               
                                 y 
                                 i 
                               
                               - 
                               
                                 z 
                                 i 
                               
                             
                             ) 
                           
                         
                         
                           3 
                            
                           
                             X 
                             0 
                           
                         
                       
                     
                     , 
                   
                 
               
               
                 
                   ( 
                   42 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           Q 
                           ~ 
                         
                         
                           i 
                           + 
                           1 
                         
                       
                       = 
                       
                         
                           
                             P 
                             0 
                           
                            
                           
                             ( 
                             
                               
                                 2 
                                  
                                 
                                   y 
                                   i 
                                 
                               
                               - 
                               
                                 x 
                                 i 
                               
                               - 
                               
                                 z 
                                 i 
                               
                             
                             ) 
                           
                         
                         
                           3 
                            
                           
                             X 
                             0 
                           
                         
                       
                     
                     , 
                   
                 
               
               
                 
                   ( 
                   43 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           R 
                           ~ 
                         
                         
                           i 
                           + 
                           1 
                         
                       
                       = 
                       
                         
                           
                             P 
                             0 
                           
                            
                           
                             ( 
                             
                               
                                 2 
                                  
                                 
                                   z 
                                   i 
                                 
                               
                               - 
                               
                                 x 
                                 i 
                               
                               - 
                               
                                 y 
                                 i 
                               
                             
                             ) 
                           
                         
                         
                           3 
                            
                           
                             X 
                             0 
                           
                         
                       
                     
                     , 
                   
                 
               
               
                 
                   ( 
                   44 
                   ) 
                 
               
             
             
               
                 
                     
                 
               
               
                 
                   ( 
                   45 
                   ) 
                 
               
             
           
         
       
     
     To study the stability of this fixed point, the map near it was linearized, 
     where X 0 =(δP 0 +β)(1+βP 0 ) −1/γc  and 
     
       
         
           
             
               
                 
                   
                     
                       x 
                       i 
                     
                     = 
                     
                       
                         
                           δ 
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     0 
                                   
                                 
                               
                               ) 
                             
                             
                               1 
                               / 
                               
                                 γ 
                                 c 
                               
                             
                           
                         
                          
                         
                           
                             P 
                             ~ 
                           
                           i 
                         
                       
                       - 
                       
                         
                           
                             β 
                              
                             
                               ( 
                               
                                 
                                   δ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     0 
                                   
                                 
                                 + 
                                 ϵ 
                               
                               ) 
                             
                           
                           
                             
                               
                                 γ 
                                 c 
                               
                                
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     β 
                                      
                                     
                                         
                                     
                                      
                                     
                                       P 
                                       0 
                                     
                                   
                                 
                                 ) 
                               
                             
                             
                               1 
                               + 
                               
                                 1 
                                 / 
                                 
                                   γ 
                                   c 
                                 
                               
                             
                           
                         
                          
                         
                           
                             R 
                             ~ 
                           
                           i 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   46 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       y 
                       i 
                     
                     = 
                     
                       
                         
                           δ 
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     0 
                                   
                                 
                               
                               ) 
                             
                             
                               1 
                               / 
                               
                                 γ 
                                 c 
                               
                             
                           
                         
                          
                         
                           
                             Q 
                             ~ 
                           
                           i 
                         
                       
                       - 
                       
                         
                           
                             β 
                              
                             
                               ( 
                               
                                 
                                   δ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     0 
                                   
                                 
                                 + 
                                 ϵ 
                               
                               ) 
                             
                           
                           
                             
                               
                                 γ 
                                 c 
                               
                                
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     β 
                                      
                                     
                                         
                                     
                                      
                                     
                                       P 
                                       0 
                                     
                                   
                                 
                                 ) 
                               
                             
                             
                               1 
                               + 
                               
                                 1 
                                 / 
                                 
                                   γ 
                                   c 
                                 
                               
                             
                           
                         
                          
                         
                           
                             P 
                             ~ 
                           
                           i 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   47 
                   ) 
                 
               
             
             
               
                 
                   
                     z 
                     i 
                   
                   = 
                   
                     
                       
                         δ 
                         
                           
                             ( 
                             
                               1 
                               + 
                               
                                 β 
                                  
                                 
                                     
                                 
                                  
                                 
                                   P 
                                   0 
                                 
                               
                             
                             ) 
                           
                           
                             1 
                             / 
                             
                               γ 
                               c 
                             
                           
                         
                       
                        
                       
                         
                           R 
                           ~ 
                         
                         i 
                       
                     
                     - 
                     
                       
                         
                           β 
                            
                           
                             ( 
                             
                               
                                 δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   P 
                                   0 
                                 
                               
                               + 
                               ϵ 
                             
                             ) 
                           
                         
                         
                           
                             
                               γ 
                               c 
                             
                              
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   
                                     P 
                                     0 
                                   
                                 
                               
                               ) 
                             
                           
                           
                             1 
                             + 
                             
                               1 
                               / 
                               
                                 γ 
                                 c 
                               
                             
                           
                         
                       
                        
                       
                         
                           
                             Q 
                             ~ 
                           
                           i 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   48 
                   ) 
                 
               
             
           
         
       
     
     Substituting these expressions, the following linear map was achieved 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       ~ 
                     
                     
                       i 
                       + 
                       1 
                     
                   
                   = 
                   
                     
                       A 
                        
                       
                         ( 
                         
                           
                             2 
                              
                             
                               
                                 P 
                                 ~ 
                               
                               i 
                             
                           
                           - 
                           
                             
                               Q 
                               ~ 
                             
                             i 
                           
                           - 
                           
                             
                               R 
                               ~ 
                             
                             i 
                           
                         
                         ) 
                       
                     
                     - 
                     
                       B 
                        
                       
                         ( 
                         
                           
                             2 
                              
                             
                               
                                 R 
                                 ~ 
                               
                               i 
                             
                           
                           - 
                           
                             
                               P 
                               ~ 
                             
                             i 
                           
                           - 
                           
                             
                               Q 
                               ~ 
                             
                             i 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   49 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         Q 
                         ~ 
                       
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         A 
                          
                         
                           ( 
                           
                             
                               2 
                                
                               
                                 
                                   Q 
                                   ~ 
                                 
                                 i 
                               
                             
                             - 
                             
                               
                                 P 
                                 ~ 
                               
                               i 
                             
                             - 
                             
                               
                                 R 
                                 ~ 
                               
                               i 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         B 
                          
                         
                           ( 
                           
                             
                               2 
                                
                               
                                 
                                   P 
                                   ~ 
                                 
                                 i 
                               
                             
                             - 
                             
                               
                                 R 
                                 ~ 
                               
                               i 
                             
                             - 
                             
                               
                                 Q 
                                 ~ 
                               
                               i 
                             
                           
                           ) 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   50 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         R 
                         ~ 
                       
                       
                         i 
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         A 
                          
                         
                           ( 
                           
                             
                               2 
                                
                               
                                 
                                   R 
                                   ~ 
                                 
                                 i 
                               
                             
                             - 
                             
                               
                                 P 
                                 ~ 
                               
                               i 
                             
                             - 
                             
                               
                                 Q 
                                 ~ 
                               
                               i 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         B 
                          
                         
                           ( 
                           
                             
                               2 
                                
                               
                                 
                                   Q 
                                   ~ 
                                 
                                 i 
                               
                             
                             - 
                             
                               
                                 P 
                                 ~ 
                               
                               i 
                             
                             - 
                             
                               
                                 R 
                                 ~ 
                               
                               i 
                             
                           
                           ) 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   51 
                   ) 
                 
               
             
             
               
                 where 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     A 
                     = 
                     
                       
                         
                           δ 
                            
                           
                               
                           
                            
                           
                             P 
                             0 
                           
                         
                         
                           3 
                            
                           
                             ( 
                             
                               
                                 δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   P 
                                   0 
                                 
                               
                               + 
                               ϵ 
                             
                             ) 
                           
                         
                       
                       = 
                       
                         1 
                         
                           3 
                            
                           
                             ( 
                             
                               1 
                               + 
                               
                                 3 
                                  
                                 
                                   αϵ 
                                   / 
                                   
                                     δγ 
                                     A 
                                   
                                 
                                  
                                 
                                   A 
                                   c 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   52 
                   ) 
                 
               
             
             
               
                 
                   B 
                   = 
                   
                     
                       
                         β 
                          
                         
                             
                         
                          
                         
                           P 
                           0 
                         
                       
                       
                         3 
                          
                         
                           
                             γ 
                             c 
                           
                            
                           
                             ( 
                             
                               1 
                               + 
                               
                                 β 
                                  
                                 
                                     
                                 
                                  
                                 
                                   P 
                                   0 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                     = 
                     
                       1 
                       
                         3 
                          
                         
                           
                             γ 
                             c 
                           
                            
                           
                             ( 
                             
                               1 
                               + 
                               
                                 
                                   3 
                                   / 
                                   
                                     βγ 
                                     A 
                                   
                                 
                                  
                                 
                                   A 
                                   c 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   53 
                   ) 
                 
               
             
           
         
       
     
     The stability of the fixed point was determined by the eigenvalues of the characteristic matrix 
     
       
         
           
             
               
                 
                   M 
                   = 
                   
                     ( 
                     
                       
                         
                           
                             
                               2 
                                
                               A 
                             
                             + 
                             B 
                           
                         
                         
                           
                             B 
                             - 
                             A 
                           
                         
                         
                           
                             
                               - 
                               A 
                             
                             - 
                             
                               2 
                                
                               B 
                             
                           
                         
                       
                       
                         
                           
                             
                               - 
                               A 
                             
                             - 
                             
                               2 
                                
                               B 
                             
                           
                         
                         
                           
                             
                               2 
                                
                               A 
                             
                             + 
                             B 
                           
                         
                         
                           
                             B 
                             - 
                             A 
                           
                         
                       
                       
                         
                           
                             B 
                             - 
                             A 
                           
                         
                         
                           
                             
                               - 
                               A 
                             
                             - 
                             
                               2 
                                
                               B 
                             
                           
                         
                         
                           
                             
                               2 
                                
                               A 
                             
                             + 
                             B 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   54 
                   ) 
                 
               
             
           
         
       
     
     This matrix has three eigenvalues: λ 1 =0; λ 2; 3 =3A+3B/2±i3 sqrt(3)B/2. The first eigenvalue is zero and corresponds to super-stability. The second and third eigenvalues are complex and can correspond to exponentially growing solutions if their absolute values |λ 2,3 |, are greater than 1, sqrt((3A+3B/2) 2 +27B 2 /4)&gt;1, or 
         A   2   +B   2   +AB&gt;  1/9
 
     This is the condition for the Hopf bifurcation in this model. It is easy to see that for small A c , the left hand side is small, but it monotonically increases with A c  to asymptotic value that is 
     
       
         
           
             
               
                 
                   
                     N 
                     sw 
                   
                   = 
                   
                     
                       
                         2 
                          
                         π 
                       
                       
                         3 
                          
                         
                             
                         
                          
                         
                           arcsin 
                            
                           
                             ( 
                             
                               3 
                                
                               
                                 3 
                               
                                
                               
                                 B 
                                 / 
                                 2 
                               
                             
                             ) 
                           
                         
                       
                     
                     = 
                     
                       
                         2 
                          
                         π 
                       
                       
                         3 
                          
                         
                             
                         
                          
                         
                           arcsin 
                           [ 
                           
                             
                               3 
                             
                             
                               2 
                                
                               
                                 
                                   γ 
                                   c 
                                 
                                  
                                 
                                   ( 
                                   
                                     1 
                                     + 
                                     
                                       
                                         3 
                                          
                                         α 
                                       
                                       
                                         
                                           βγ 
                                           A 
                                         
                                          
                                         
                                           A 
                                           c 
                                         
                                       
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   55 
                   ) 
                 
               
             
           
         
       
     
     greater than 1/9, so the Hopf bifurcation always occurs at some finite A c  (see  FIG. 8A ). At the Hopf bifurcation, where λ 2,3 |=1, the number of lysis events per one switching cycle (⅓ of a period) is  FIGS. 8B and 8C  show the number of lysis pulses and bifurcation diagram for the map and the underlying full model.
 
Strongly switching regime.
 
     Far away from the Hopf bifurcation point, the switching becomes strongly nonlinear, when one strain dominates the dynamics for many lysis periods before rapidly switching to the next strain domination, and so on ( FIGS. 25, 26 ). To characterize the dynamics in this regime, the time interval between lysis events and the duration of switching cycles was computed. 
     The lysis intervals vary within a switching cycle. They are smallest in the middle of the cycle, when one strain is strongly dominating, and are somewhat longer between the cycles, when two of the strains are nearly equal. 
     Minimum lysis interval. In the bulk of each switching cycle, one of the strains grows to high concentration at which the lysis occurs, while the other two remain much smaller (it is assumed that ε&lt;&lt;γ A A/α). In this regime, the map became nearly one-dimensional and trivial (without loss of generality p was chosen to be the dominating strain and Q i =R i =0 was 
         P   i =γ A   A   c α −1   =P   M ,  (56)
 
     assumed):
 
[it was assumed that we assume that ε&lt;&lt;δγ A A/α. The interval between lysis events during this phase is as expected.
 
     Maximum lysis interval. Maximum lysis interval occurs during the switch from one strain 
     
       
         
           
             
               
                 
                   
                     T 
                     m 
                   
                   = 
                   
                     
                       log 
                        
                       
                         [ 
                         
                           
                             P 
                             M 
                           
                           
                             
                               δ 
                                
                               
                                   
                               
                                
                               
                                 P 
                                 M 
                               
                             
                             + 
                             
                               3 
                                
                               ϵ 
                             
                           
                         
                         ] 
                       
                     
                     = 
                     
                       
                         - 
                         
                           log 
                            
                           
                             [ 
                             
                               δ 
                               + 
                               
                                 
                                   3 
                                    
                                   ϵα 
                                 
                                 
                                   
                                     γ 
                                     A 
                                   
                                    
                                   
                                     A 
                                     c 
                                   
                                 
                               
                             
                             ] 
                           
                         
                       
                       ≈ 
                       
                         
                           - 
                           log 
                         
                          
                         
                             
                         
                          
                         
                           δ 
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   57 
                   ) 
                 
               
             
           
         
       
     
     dominance to the next strain. During this switch, two of the concentrations briefly become equal at a certain i=k+1 (suppose, for definitiveness, P k+1 =Q k+1 , R k+1 =0). It is easy to see that the condition of equality P k+1 =Q k+1  is 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       k 
                     
                     
                       
                         ( 
                         
                           1 
                           + 
                           
                             β 
                              
                             
                                 
                             
                              
                             
                               R 
                               k 
                             
                           
                         
                         ) 
                       
                       
                         1 
                         / 
                         
                           γ 
                           c 
                         
                       
                     
                   
                   = 
                   
                     R 
                     k 
                   
                 
               
               
                 
                   ( 
                   58 
                   ) 
                 
               
             
           
         
       
     
     (small ε was neglected here). For sufficiently sharp switch, the magnitude P k  is still close to P M =γ A A c /α. That allowed solving for R k  which can then be used to find T k . If βR k &gt;&gt;1 (to be verified a posteriori) 1 can be neglected and the equation can be solved explicitly, 
     
       
         
           
             
               
                 
                   
                     R 
                     k 
                   
                   ≈ 
                   
                     
                       
                         β 
                         1 
                       
                        
                       
                         ( 
                         
                           β 
                            
                           
                               
                           
                            
                           
                             P 
                             0 
                           
                         
                         ) 
                       
                     
                     
                       
                         γ 
                         c 
                       
                       
                         
                           γ 
                           c 
                         
                         + 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   59 
                   ) 
                 
               
             
           
         
       
     
     From here, the condition of validity of this expression for γ c ˜1 is βγ A A c α&gt;&gt;1. The maximum lysis interval was then computed explicitly 
     
       
         
           
             
               
                 
                   
                     T 
                     M 
                   
                   = 
                   
                     
                       log 
                        
                       
                         ( 
                         
                           
                             P 
                             M 
                           
                           
                             2 
                              
                             
                               
                                 
                                   δβ 
                                   
                                     - 
                                     1 
                                   
                                 
                                  
                                 
                                   ( 
                                   
                                     
                                       P 
                                       M 
                                     
                                      
                                     β 
                                   
                                   ) 
                                 
                               
                               
                                 
                                   γ 
                                   c 
                                 
                                 / 
                                 
                                   ( 
                                   
                                     
                                       γ 
                                       c 
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         
                           - 
                           log 
                         
                          
                         
                             
                         
                          
                         δ 
                       
                       - 
                       
                         log 
                          
                         
                             
                         
                          
                         2 
                       
                       - 
                       
                         
                           
                             ( 
                             
                               
                                 γ 
                                 c 
                               
                               + 
                               1 
                             
                             ) 
                           
                           
                             - 
                             1 
                           
                         
                          
                         
                           
                             log 
                              
                             
                               ( 
                               
                                 
                                   βγ 
                                   A 
                                 
                                  
                                 
                                   
                                     A 
                                     c 
                                   
                                   / 
                                   α 
                                 
                               
                               ) 
                             
                           
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   60 
                   ) 
                 
               
             
           
         
       
     
     The average lysis interval T a  is somewhere between T m  and T M , but progressively approaches T m  as the switching intervals become longer. 
     Switching interval duration. To estimate the duration of the switching cycles, in which one strain dominates, it was observed that that it consists of two sub-intervals. In the first sub-interval, one of the strains (p, for specificity) is dominating and remains close to P M  before the lysis events, while the other two strains (q and r) are small. One of them (q) remains very small (O(ε)) throughout the whole sub-interval since its growth is strongly suppressed by large p, while the other strain (r) is not suppressed and steadily grows from small initial level to O(P M ) to eventually reach amplitudes comparable with P M . Once this happens, the second sub-interval commences during which the amplitude of the first strain (p) gets quickly reduced to small (O(ε)) because its growth is now suppressed by large r. To obtain the duration of the first sub-interval, the mapping for R i  was considered, assuming that Q i ≈0, P i    
         R   i+1   =δe   T     i   ( R   i +ϵ/δ)  (61)
 
     ≈P M    
     According to Eq. (32), 
     
       
         
           
             
               
                 
                   
                     
                       e 
                       
                         T 
                         i 
                       
                     
                      
                     
                       
                         δ 
                          
                         
                             
                         
                          
                         
                           P 
                           M 
                         
                       
                       
                         
                           ( 
                           
                             1 
                             + 
                             
                               β 
                                
                               
                                   
                               
                                
                               
                                 R 
                                 i 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           
                             γ 
                             c 
                           
                         
                       
                     
                   
                   ≈ 
                   
                     P 
                     M 
                   
                 
               
               
                 
                   ( 
                   62 
                   ) 
                 
               
             
           
         
       
     
     Using this expression in Eq. (31), the following 1D mapping was obtained 
         R   i+1 =( R   i +ϵ/δ)(1+β R   i ) 1/γ     c     (63)
 
     To find the duration of the first sub-interval, the number of iterations in which R i  reaches the value of the order of P M  starting from R 0 =0 was determined. This sub-interval itself can be broken into two parts. While βR i &lt;&lt;1, the second bracket was expanded to obtain the following quadratic map 
         R   i+1 =|( R   i +ϵ/δ)(1+βγ c   −1   R   i )  (64)
 
     or introducing new variable {circumflex over (R)} i =βγ c   −1 R i    
         {circumflex over (R)}   i+1 =( {circumflex over (R)}   i +α)(1+ {circumflex over (R)}   i )  (65)
 
     with a=εβ/δγ c  and initial condition {circumflex over (R)} 0 =0. For small a&lt;&lt;1, the number of iterations n to reach {circumflex over (R)} n =1/γc. is large and can be estimated by taking a continuous limit and integrating the following differential equation
 
from {circumflex over (R)}=0 to {circumflex over (R)}=1, which for small a yields
 
     Of course, the last few iterations the condition βR i &lt;&lt;1 is violated, but this expression still 
     
       
         
           
             
               
                 
                   
                     
                       d 
                        
                       
                           
                       
                        
                       
                         R 
                         ^ 
                       
                     
                     dt 
                   
                   = 
                   
                     a 
                     + 
                     
                       a 
                        
                       
                           
                       
                        
                       
                         R 
                         ^ 
                       
                     
                     + 
                     
                       
                         R 
                         ^ 
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   66 
                   ) 
                 
               
             
             
               
                 
                   n 
                   ≈ 
                   
                     
                       
                         tan 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             γ 
                             c 
                             
                               - 
                               1 
                             
                           
                           / 
                           
                             a 
                           
                         
                         ) 
                       
                     
                     
                       a 
                     
                   
                 
               
               
                 
                   ( 
                   67 
                   ) 
                 
               
             
           
         
       
     
     gave a good estimation of the number of iteration needed to reach R n =β −1 . Next was 
           R     i+1   ≈ R     i (1+   R     i ) 1/γ     c     (68)
 
     estimated the number of additional iterations for R i  to go from R n =β −1  to P M . Since by assumption β&gt;&gt;ε/δ in this range of R i  the latter was neglected from the map (63) and it was simplified to
 
where  R   i =βR i , with initial condition  R   n =1. The first several iterates of this map were as follows:  R   n+1 =2 1/γc ,  R   n+2 =[2(1+2 1/γc )] 1/γc ,  R   n+3 =[2(1+2 1/γc )(1+[2(1+2 1/γc )] 1/γc )] 1/γc , etc. For γ c =O(1), this sequence rapidly (super-exponentially) grows with i, and so already after i=n+2, 1 was neglected in the brackets of Eq.(68) and written simply as
 
           R     i+1   ≈ R     i   1/γ     c     +1   (69)
 
     Thus, at N 1  iteration, 
     
       
         
           
             
               
                 R 
                 _ 
               
               
                 N 
                 1 
               
             
             = 
             
               
                 
                   [ 
                   
                     
                       R 
                       _ 
                     
                     
                       n 
                       + 
                       2 
                     
                   
                   ] 
                 
                 
                   
                     ( 
                     
                       1 
                       + 
                       
                         γ 
                         c 
                         
                           - 
                           1 
                         
                       
                     
                     ) 
                   
                   
                     
                       N 
                       c 
                     
                     - 
                     n 
                     + 
                     2 
                   
                 
               
               = 
               
                 
                   [ 
                   
                     2 
                      
                     
                       ( 
                       
                         1 
                         + 
                         
                           2 
                           
                             1 
                             / 
                             
                               γ 
                               c 
                             
                           
                         
                       
                       ) 
                     
                   
                   ] 
                 
                 
                   
                     
                       γ 
                       c 
                       
                         - 
                         1 
                       
                     
                      
                     
                       ( 
                       
                         1 
                         + 
                         
                           γ 
                           c 
                           
                             - 
                             1 
                           
                         
                       
                       ) 
                     
                   
                   
                     
                       N 
                       c 
                     
                     - 
                     n 
                     - 
                     2 
                   
                 
               
             
           
         
       
     
     Equating this expression with PM and recalling the expression for n, the following approximate formula for N 1  was obtained, 
     
       
         
           
             
               
                 
                   
                     N 
                     1 
                   
                   ≈ 
                   
                     
                       
                         
                           tan 
                           
                             - 
                             1 
                           
                         
                          
                         
                           ( 
                           
                             
                               δ 
                               / 
                               
                                 ϵβγ 
                                 C 
                               
                             
                           
                           ) 
                         
                       
                       
                         
                           ϵβ 
                           / 
                           
                             δγ 
                             c 
                           
                         
                       
                     
                     + 
                     
                       
                         log 
                          
                         
                           [ 
                           
                             
                               
                                 γ 
                                 c 
                               
                                
                               
                                 log 
                                  
                                 
                                   ( 
                                   
                                     
                                       βγ 
                                       A 
                                     
                                      
                                     
                                       A 
                                       c 
                                     
                                      
                                     α 
                                   
                                   ) 
                                 
                               
                             
                             
                               log 
                                
                               
                                 [ 
                                 
                                   2 
                                    
                                   
                                     ( 
                                     
                                       1 
                                       + 
                                       
                                         2 
                                         
                                           1 
                                           / 
                                           
                                             γ 
                                             c 
                                           
                                         
                                       
                                     
                                     ) 
                                   
                                 
                                 ] 
                               
                             
                           
                           ] 
                         
                       
                       
                         log 
                          
                         
                           ( 
                           
                             1 
                             + 
                             
                               γ 
                               c 
                               
                                 - 
                                 1 
                               
                             
                           
                           ) 
                         
                       
                     
                     + 
                     2 
                   
                 
               
               
                 
                   ( 
                   70 
                   ) 
                 
               
             
           
         
       
     
     During the second sub-interval, the magnitude R i  is already near P M , and so the growth of strain P is strongly suppressed. It means that at each lysis event it is reduced by factor δ, P i+1 =δP i , This immediately yielded the estimate for the number of iterations needed for P i  to reach the “background” level O(ε), 
     
       
         
           
             
               N 
               2 
             
             ≈ 
             
               
                 log 
                  
                 
                     
                 
                  
                 
                   ( 
                   
                     ϵ 
                      
                     
                         
                     
                      
                     
                       P 
                       M 
                       
                         - 
                         1 
                       
                     
                   
                   ) 
                 
               
               
                 log 
                  
                 
                     
                 
                  
                 δ 
               
             
           
         
       
     
     Thus, the total number of lysis intervals within a single switching cycle is given by 
     
       
         
           
             
               
                 
                   
                     N 
                     sw 
                   
                   ≈ 
                   
                     
                       
                         
                           tan 
                           
                             - 
                             1 
                           
                         
                          
                         
                           ( 
                           
                             
                               δ 
                               / 
                               
                                 ϵβγ 
                                 c 
                               
                             
                           
                           ) 
                         
                       
                       
                         
                           ϵβ 
                           / 
                           
                             δγ 
                             c 
                           
                         
                       
                     
                     + 
                     
                       
                         log 
                          
                         
                           [ 
                           
                             
                               
                                 γ 
                                 c 
                               
                                
                               
                                 log 
                                  
                                 
                                   ( 
                                   
                                     
                                       βγ 
                                       A 
                                     
                                      
                                     
                                       A 
                                       c 
                                     
                                      
                                     α 
                                   
                                   ) 
                                 
                               
                             
                             
                               log 
                                
                               
                                 [ 
                                 
                                   2 
                                    
                                   
                                     ( 
                                     
                                       1 
                                       + 
                                       
                                         2 
                                         
                                           1 
                                           / 
                                           
                                             γ 
                                             c 
                                           
                                         
                                       
                                     
                                     ) 
                                   
                                 
                                 ] 
                               
                             
                           
                           ] 
                         
                       
                       
                         log 
                          
                         
                           ( 
                           
                             1 
                             + 
                             
                               γ 
                               c 
                               
                                 - 
                                 1 
                               
                             
                           
                           ) 
                         
                       
                     
                     + 
                     2 
                     + 
                     
                       
                         log 
                          
                         
                             
                         
                          
                         
                           ( 
                           
                             ϵ 
                              
                             
                                 
                             
                              
                             
                               P 
                               M 
                               
                                 - 
                                 1 
                               
                             
                           
                           ) 
                         
                       
                       
                         log 
                          
                         
                             
                         
                          
                         δ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   71 
                   ) 
                 
               
             
           
         
       
     
       FIGS. 8D-8G  show the interval between lysis events (minimal, maximal, and average) and the number of lysis events per one switching interval as functions of some model parameters, obtained from the exact model, the 3D map, and the analytical approximations. Surprisingly, the analytical approximations appeared more accurate than the 3D map results. 
     REFERENCES 
     
         
         1. Gravel, D. et al. Experimental niche evolution alters the strength of the diversity-productivity relationship. Nature 469, 89-92 (2011). 
         2. De Roy, K. et al. Environmental conditions and community evenness determine the outcome of biological invasion. Nature communications 4, 1383 (2013). 
         3. Tanouchi, Y., Smith, R. P. &amp; You, L. Engineering microbial systems to explore ecological and evolutionary dynamics. Current opinion in biotechnology 23, 791-797 (2012). 
         4. Wintermute, E. H. &amp; Silver, P. A. Emergent cooperation in microbial metabolism. Molecular systems biology 6, 407 (2010). 
         5. Klitgord, N. &amp; Segre, D. Environments that induce synthetic microbial ecosystems. PLoS Comput Biol 6, e1001002 (2010). 
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         7. De Roy, K., Marzorati, M., Van den Abbeele, P., Van de Wiele, T. &amp; Boon, N. Synthetic microbial ecosystems: an exciting tool to understand and apply microbial communities. Environmental microbiology 16, 1472-1481 (2014). 
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         9. Elowitz, M. B. &amp; Leibler, S. A synthetic oscillatory network of transcriptional regulators. Nature 403, 335-338 (2000). 
         10. Hasty, J., McMillen, D. &amp; Collins, J. J. Engineered gene circuits. Nature 420, 224-230 (2002). 
         11. Endy, D. Foundations for engineering biology. Nature 438, 449-453 (2005). 
         12. You, L., Cox, R. S., Weiss, R. &amp; Arnold, F. H. Programmed population control by cell-cell communication and regulated killing. Nature 428, 868-871 (2004). 
         13. Brenner, K., Karig, D. K., Weiss, R. &amp; Arnold, F. H. Engineered bidirectional communication mediates a consensus in a microbial biofilm consortium. Proceedings of the National Academy of Sciences 104, 17300-17304 (2007). 
         14. Danino, T., Mondragón-Palomino, O., Tsimring, L. &amp; Hasty, J. A synchronized quorum of genetic clocks. Nature 463, 326-330 (2010). 
         15. Chen, Y., Kim, J. K., Hirning, A. J., Josic, K. &amp; Bennett, M. R. Emergent genetic oscillations in a synthetic microbial consortium. Science 349, 986-989 (2015). 
         16. Din, M. O. et al. Synchronized cycles of bacterial lysis for in vivo delivery. Nature 536, 81-85 (2016). 
       
    
     Other Embodiments 
     Embodiment 1 is a method comprising: 
     culturing a first bacterial strain for a first period of time in a growth environment; 
     adding a second bacterial strain to the growth environment and culturing the second bacterial strain for a second period of time; 
     adding a third bacterial strain to the growth environment and culturing the third bacterial strain for a third period of time, 
     wherein each of the first, second, and third bacterial strains comprises a toxin system; 
     wherein the toxin system of the first bacterial strain produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin; 
     wherein the toxin system of the second bacterial strain produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin; and 
     wherein the toxin system of the third bacterial strain produces a third toxin/third antitoxin pair and the second antitoxin from the second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, and 
     optionally wherein each of the first, second, and third bacterial strains comprises
         a lysis plasmid having a lysis gene under the control of an activatable promoter; and   an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum-sensing molecule,       

     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum-sensing molecule. 
     Embodiment 2 is the method of embodiment 1, wherein the quorum-sensing molecule is different in each of the first, second, and third bacterial strains.
 
Embodiment 3 is the method of embodiment 2, wherein each quorum-sensing molecule of each of the first, second, and third bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another strain.
 
Embodiment 4 is the method of embodiment 1, wherein the quorum-sensing molecule is the same in each of the first, second, and third bacterial strains.
 
Embodiment 5 is the method of any one of embodiments 1-4, further comprising culturing or co-culturing one or more additional bacterial strains in the growth environment.
 
Embodiment 6 is the method of embodiment 5, wherein each of the one or more additional bacterial strains comprise:
 
     a lysis plasmid having a lysis gene under the control of an activatable promoter; and 
     an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum-sensing molecule, 
     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum-sensing molecule. 
     Embodiment 7 is the method of embodiment 6, wherein the quorum-sensing molecule is different in each of the first, second, third, and one or more additional bacterial strains.
 
Embodiment 8 is the method of embodiment 7, wherein each quorum-sensing molecule of each of the first, second, third, and one or more additional bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another bacterial strain used in the growth environment.
 
Embodiment 9 is the method of embodiment 6, wherein the quorum sensing molecule is the same in each of the first, second, third, and one or more additional bacterial strains.
 
Embodiment 10 is the method of any one of embodiments 6-9, wherein each of the one or more additional bacterial strains comprises a toxin system.
 
Embodiment 11 is the method of any one of embodiments 1-10, wherein the toxin system of the first bacterial strain, the second bacterial strain, the third bacterial strain, and each of the one or more additional bacterial strains is independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 12 is the method of any one of embodiments 1-11, wherein the lysis plasmid and activator plasmid of each of the at least first, second, and third bacterial strains are copies of the same plasmid.
 
Embodiment 13 is the method of any one of embodiments 1-11, wherein the lysis plasmid and activator plasmid of each of the at least the first, second, and third bacterial strains are different plasmids.
 
Embodiment 14 is the method of any one of embodiments 1-13, wherein at least the first, second, and third bacterial strains are metabolically competitive.
 
Embodiment 15 is the method of any one of embodiments 1-14, wherein at least the first, second, and third bacterial strains are selected from  E. coli, S. typhimurium , or a bacterial variant thereof.
 
Embodiment 16 is the method of any one of embodiments 1-15, wherein each of the at least the first, second, and third bacterial strains does not have a growth advantage compared to another strain in the growth environment.
 
Embodiment 17 is the method of any one of embodiments 1-16, wherein in each of the at least the first, second, and third bacterial strains the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, optionally a degradation tag, and optionally a reporter gene.
 
Embodiment 18 is the method of any one of embodiments 1-17, wherein the lysis gene in each of the at least the first, second, and third bacterial strains is E from a bacteriophage ΦX174.
 
Embodiment 19 is the method of any one of embodiments 1-18, wherein the activatable promoter in each of the at least the first, second, and third bacterial strains is a LuxR-AHL activatable luxI promoter and the activator gene is a LuxI.
 
Embodiment 20 is the method of embodiment 17, wherein at least one reporter gene is selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof.
 
Embodiment 21 is the method of embodiment 17, wherein the degradation tag is an ssrA-LAA degradation tag.
 
Embodiment 22 is the method of any one of embodiments 1-21, wherein at least one of the plasmids is integrated into a genome of at least one of the first, second, and third bacterial strains.
 
Embodiment 23 is the method of any one of embodiments 1-22, wherein the culturing occurs in a microfluidic device.
 
Embodiment 24 is the method of any one of embodiments 1-22, wherein the culturing occurs in a bioreactor.
 
Embodiment 25 is the method of any one of embodiments 1-22, wherein the culturing occurs in vivo.
 
Embodiment 26 is the method of any one of embodiments 1-25, wherein each of the first, second, and third periods of time ranges from about 12 to about 72 hours.
 
Embodiment 27 is the method of any one of embodiments 1-25, wherein each of the first, second, and third periods of time is selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours.
 
Embodiment 28 is the method of any one of embodiments 1-25, wherein each of the first, second, and third periods of time is selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours.
 
Embodiment 29 is the method of any one of embodiments 1-25, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 72 hours.
 
Embodiment 30 is the method of embodiment 29, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 48 hours.
 
Embodiment 31 is the method of embodiment 29, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 24 hours.
 
Embodiment 32 is the method of embodiment 29, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 18 hours.
 
Embodiment 33 is the method of embodiment 29, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 12 hours.
 
Embodiment 34 is the method of embodiment 29, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 6 hours.
 
Embodiment 35 is the method of embodiment 29, wherein each of the first, second, and third periods of time independently ranges from about 1 hours to about 3 hours.
 
Embodiment 36 is the method of any one of embodiments 1-35, wherein the first, second, and third periods of time occur sequentially.
 
Embodiment 37 is the method of any one of embodiments 1-36, wherein the first and second, second and third, or first and third periods of time partially or completely overlap.
 
Embodiment 38 is the method of any one of embodiments 1-37, wherein one or more of the first, second, and third bacterial strains encodes a heterologous nucleic acid and/or a heterologous protein operably linked to a promoter.
 
Embodiment 39 is the method of embodiment 38, wherein the promoter is an activatable promoter.
 
Embodiment 40 is the method of embodiment 39, wherein the promoter is activated by the quorum sensing molecule.
 
Embodiment 41 is the method of embodiment 38, wherein the promoter is a constitutive promoter.
 
Embodiment 42 is the method of any one of embodiments 38-41, wherein the heterologous nucleic acid and/or heterologous protein is a therapeutic agent.
 
Embodiment 43 is the method of embodiment 42, wherein the therapeutic agent is selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof.
 
Embodiment 44 is the method of embodiment 43, wherein the inhibitory nucleic acid is siRNA, shRNA, miRNA, or antisense.
 
Embodiment 45 is a method comprising:
 
     providing n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     co-culturing each of the bacterial strains sequentially for an independent period of time in a growth environment; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises
         a lysis plasmid having a lysis gene under the control of an activatable promoter; and   an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule,       

     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein each of the n bacterial strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 46 is the method of embodiment 45, wherein in each of the n bacterial strains, the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, optionally a degradation tag, and optionally a reporter gene.
 
Embodiment 47 is the method of any one of embodiments 45-46, wherein the lysis gene in each of the n bacterial strains is E from a bacteriophage ΦX174.
 
Embodiment 48 is the method of any one of embodiments 45-47, wherein the activatable promoter in each of the n bacterial strains is a LuxR-AHL activatable luxI promoter and the activator gene is a LuxI.
 
Embodiment 49 is the method of embodiment 46, wherein at least one reporter gene is selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof.
 
Embodiment 50 is the method of embodiment 46, wherein the degradation tag is an ssrA-LAA degradation tag.
 
Embodiment 51 is the method of any one of embodiments 45-50, wherein at least one of the plasmids is integrated into a genome of at least one of the n bacterial strains.
 
Embodiment 52 is the method of any one of embodiments 45-51, wherein the quorum-sensing molecule is different in each of the n bacterial strains.
 
Embodiment 53 is the method of embodiment 52, wherein each quorum-sensing molecule of each of the n bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another strain.
 
Embodiment 54 is the method of any one of embodiments 45-51, wherein the quorum-sensing molecule is the same in each of the n bacterial strains.
 
Embodiment 55 is the method of any one of embodiments 45-54, wherein the lysis plasmid and activator plasmid of each of then bacterial strains are copies of the same plasmid.
 
Embodiment 56 is the method of any one of embodiments 45-54, wherein the lysis plasmid and activator plasmid of each of the n bacterial strains are different plasmids.
 
Embodiment 57 is a method comprising:
 
     providing n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     co-culturing each of the bacterial strains sequentially for an independent period of time in a growth environment; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n bacterial strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 58 is the method of any one of embodiments 44-57, wherein the n bacterial strains are metabolically competitive.
 
Embodiment 59 is the method of any one of embodiments 44-58, wherein each of the n bacterial strains are selected from  E. coli, S. typhimurium , or a bacterial variant thereof.
 
Embodiment 60 is the method of any one of embodiments 44-59, wherein each of the n bacterial strains does not have a growth advantage compared to another strain in the growth environment.
 
Embodiment 61 is the method of any one of embodiments 44-60, wherein the toxin system of the n bacterial strains is independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 62 is the method of any one of embodiments 44-61, wherein the culturing occurs in a microfluidic device.
 
Embodiment 63 is the method of any one of embodiments 44-61, wherein the culturing occurs in a bioreactor.
 
Embodiment 64 is the method of any one of embodiments 44-61, wherein the culturing occurs in vivo.
 
Embodiment 65 is the method of any one of embodiments 44-64, wherein each of the independent periods of time ranges from about 12 to about 72 hours.
 
Embodiment 66 is the method of any one of embodiments 44-64, wherein each of the independent periods of time is selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours.
 
Embodiment 67 is the method of any one of embodiments 44-64, wherein each of the independent periods of time is selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours.
 
Embodiment 68 is the method of any one of embodiments 44-64, wherein each of the periods of time independently ranges from about 1 hours to about 72 hours.
 
Embodiment 69 is the method of embodiment 68, wherein each of the periods of time independently ranges from about 1 hours to about 48 hours.
 
Embodiment 70 is the method of embodiment 68, wherein each of the periods of time independently ranges from about 1 hours to about 24 hours.
 
Embodiment 71 is the method of embodiment 68, wherein each of the periods of time independently ranges from about 1 hours to about 18 hours.
 
Embodiment 72 is the method of embodiment 68, wherein each of the periods of time independently ranges from about 1 hours to about 12 hours.
 
Embodiment 73 is the method of embodiment 68, wherein each of the periods of time independently ranges from about 1 hours to about 6 hours.
 
Embodiment 74 is the method of embodiment 68, wherein each of the periods of time independently ranges from about 1 hours to about 3 hours.
 
Embodiment 75 is the method of any one of embodiments 45-74, wherein one or more of the periods of time partially or completely overlap.
 
Embodiment 76 is the method of any one of embodiments 45-75, wherein one or more of the n bacterial strains encodes a heterologous nucleic acid and/or a heterologous protein operably linked to a promoter.
 
Embodiment 77 is the method of embodiment 76, wherein the promoter is an activatable promoter.
 
Embodiment 78 is the method of embodiment 77, wherein the activatable promoter is activated by a quorum-sensing molecule.
 
Embodiment 79 is the method of embodiment 76, wherein the promoter is a constitutive promoter.
 
Embodiment 80 is the method of any one of embodiments 76-79, wherein the heterologous nucleic acid and/or heterologous protein is a therapeutic agent.
 
Embodiment 81 is the method of embodiment 80, wherein the therapeutic agent is selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof.
 
Embodiment 82 is the method of embodiment 81, wherein the inhibitory nucleic acid is siRNA, shRNA, miRNA, or antisense.
 
Embodiment 83 is the method of any one of embodiments 45-82, wherein each of the second bacterial strain through the nth bacterial strain does not produce the second toxin of the toxin system of the previous strain, and the first bacterial strain does not produce the fourth toxin of the toxin system of the nth bacterial strain.
 
Embodiment 84 is a bacterial strain comprising a lysis plasmid and an activator plasmid; wherein the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, optionally a degradation tag, and optionally a reporter gene; wherein the bacterial strain further comprises a toxin system; wherein the toxin system produces a first toxin/first antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the bacterial strain does not produce the second toxin.
 
Embodiment 85 is the bacterial strain of embodiment 84, wherein the lysis gene is E from a bacteriophage ΦX174.
 
Embodiment 86 is the bacterial strain of any one of embodiments 84-85, wherein the activatable promoter is a LuxR-AHL activatable luxI promoter and the activator gene is a LuxI.
 
Embodiment 87 is the bacterial strain of any one of embodiments 84-86, wherein the activator gene encodes a molecule that activates, directly or indirectly, the activatable promoter.
 
Embodiment 88 is the bacterial strain of embodiment 87, wherein the molecule that activates, directly or indirectly, the activatable promoter is a quorum-sensing molecule.
 
Embodiment 89 is the bacterial strain of any one of embodiments 84-88, wherein the lysis gene is operably linked to the activatable promoter.
 
Embodiment 90 is the bacterial strain of any one of embodiments 84-89, wherein the reporter gene on the lysis plasmid is operably linked to the activatable promoter.
 
Embodiment 91 is the bacterial strain of any one of embodiments 84-90, wherein the activator plasmid further comprises an activatable promoter.
 
Embodiment 92 is the bacterial strain of embodiment 91, wherein the activatable promoter of the activator plasmid is a copy of the activatable promoter of the lysis plasmid.
 
Embodiment 93 is the bacterial strain of any one of embodiments 91-92, wherein the activator gene is operably linked to the activatable promoter of the activator plasmid.
 
Embodiment 94 is the bacterial strain of any one of embodiments 91-93, wherein the reporter gene of the activator plasmid is operably linked to the activatable promoter of the activator plasmid.
 
Embodiment 95 is the bacterial strain of any one of embodiments 91-94, wherein the degradation tag is operably linked to the activatable promoter of the activator plasmid.
 
Embodiment 96 is the bacterial strain of any one of embodiments 84-95, wherein the toxin system is operably linked to the activatable promoter of the lysis plasmid.
 
Embodiment 97 is the bacterial strain of any one of embodiments 84-96, wherein the degradation tag is an ssrA-LAA degradation tag.
 
Embodiment 98 is the bacterial strain of any one of embodiments 84-97, wherein the reporter gene of the lysis plasmid, the reporter gene of the activator plasmid, or both, are fluorescent proteins.
 
Embodiment 99 is the bacterial strain of any one of embodiments 84-97, wherein the reporter gene of the lysis plasmid and the reporter gene of the activator plasmid are different genes.
 
Embodiment 100 is a bacterial strain comprising a toxin system; wherein the toxin system produces a first toxin/first antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the bacterial strain does not produce the second toxin.
 
Embodiment 101 is the bacterial strain of any one of embodiments 84-100, wherein the bacterial strain encodes a heterologous nucleic acid and/or a heterologous protein operably linked to a promoter.
 
Embodiment 102 is the bacterial strain of embodiment 101, wherein the promoter is an activatable promoter.
 
Embodiment 103 is the bacterial strain of embodiment 102, wherein the activatable promoter is activated by a quorum-sensing molecule.
 
Embodiment 104 is the bacterial strain of embodiment 101, wherein the promoter is a constitutive promoter.
 
Embodiment 105 is the bacterial strain of any one of embodiments 101-104, wherein the heterologous nucleic acid and/or heterologous protein is a therapeutic agent.
 
Embodiment 106 is the bacterial strain of any one of embodiments 84-105, wherein the toxin system is encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 107 is the bacterial strain of any one of embodiments 84-106, wherein the bacterial strain further comprises a nucleic acid encoding a therapeutic agent.
 
Embodiment 108 is the bacterial strain of embodiment 105 or embodiment 107, wherein the therapeutic agent is selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof.
 
Embodiment 109 is the bacterial strain of any one of embodiments 105 or embodiments 107-108, wherein the therapeutic agent is a therapeutic polypeptide.
 
Embodiment 110 is the bacterial strain of any one of embodiments 105 or embodiments 107-109, wherein the therapeutic agent is cytotoxic or cytostatic to a target cell.
 
Embodiment 111 is the bacterial strain of embodiment 110, wherein the target cell is a cancer cell or an infected cell.
 
Embodiment 112 is a pharmaceutical composition comprising any one or more of the bacterial strains of embodiments 84-111.
 
Embodiment 113 is the pharmaceutical composition of embodiment 112, wherein the pharmaceutical composition is formulated for in situ drug delivery.
 
Embodiment 114 is a system comprising:
 
     a first bacterial strain comprising a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; wherein the first bacterial strain further comprises a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin; 
     a second bacterial strain comprising a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, optionally a second degradation tag, and optionally a second reporter gene; wherein the second bacterial strain further comprises a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin; and 
     a third bacterial strain comprising a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene; wherein the third bacterial strain further comprises a third toxin system; wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Embodiment 115 is a system comprising: 
     a first bacterial strain comprising a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further comprises a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; 
     a second bacterial strain comprising a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further comprises a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, optionally a second degradation tag, and optionally a second reporter gene; and 
     a third bacterial strain comprising a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further comprises a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Embodiment 116 is the system of embodiment 114 or embodiment 115, further comprising one or more additional bacterial strains.
 
Embodiment 117 is the system of any one of embodiments 114-116, wherein the first toxin system, the second toxin system, and the third toxin system are independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 118 is a system comprising:
 
     n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 119 is a system comprising: 
     n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises
         a lysis plasmid having a lysis gene under the control of an activatable promoter; and   an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule,       

     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein each of the n bacterial strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 120 is the system of embodiment 118 or embodiment 119, where n is 3.
 
Embodiment 121 is the system of embodiment 118 or embodiment 119, wherein n is 4, 5, 6, 7, 8, 9, or 10.
 
Embodiment 122 is the system of any one of embodiments 118-121, wherein each of the toxin systems are independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 123 is the system of any one of embodiments 118-122, wherein each of the second bacterial strain through the nth bacterial strain does not produce the second toxin of the toxin system of the previous strain, and the first bacterial strain does not produce the fourth toxin of the toxin system of the nth bacterial strain.
 
Embodiment 124 is a kit comprising:
 
     a first pharmaceutical composition comprising a first bacterial strain comprising a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, a first degradation tag, and optionally a first reporter gene; wherein the first bacterial strain further comprises a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin; 
     a second pharmaceutical composition comprising a second bacterial strain comprising a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, a second degradation tag, and optionally a second reporter gene; wherein the second bacterial strain further comprises a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin; and 
     a third pharmaceutical composition comprising a third bacterial strain comprising a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, a third degradation tag, and optionally a third reporter gene; wherein the third bacterial strain further comprises a third toxin system; wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Embodiment 125 is a kit comprising: 
     a first pharmaceutical composition comprising a first bacterial strain comprising a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further comprises a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; 
     a second pharmaceutical composition comprising second bacterial strain comprising a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further comprises a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, optionally a second degradation tag, and optionally a second reporter gene; and 
     a third pharmaceutical composition comprising a third bacterial strain comprising a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further comprises a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Embodiment 126 is the kit of any one of embodiments 124-125, wherein the first toxin system, the second toxin system, and the third toxin system are independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 127 is the kit of any one of embodiments 124-125, further comprising one or more additional bacterial strains in the first, second, third, and/or one or more additional pharmaceutical compositions.
 
Embodiment 128 is a kit comprising:
 
     n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 129 is a kit comprising: 
     n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises
         a lysis plasmid having a lysis gene under the control of an activatable promoter; and   an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule,       

     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the lysis plasmid of each of then bacterial strains comprises a toxin system; 
     wherein the toxin system of the lysis plasmid of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the lysis plasmid of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 130 is the kit of embodiment 128 or embodiment 129, where n is 3.
 
Embodiment 131 is the kit of embodiment 128 or embodiment 129, wherein n is 4, 5, 6, 7, 8, 9, or 10.
 
Embodiment 132 is a drug delivery system comprising the system of embodiments 114-123 or kit of embodiments 124-131.
 
Embodiment 133 is a periodic drug delivery system comprising the system of embodiments 114-123 or kit of embodiments 124-131.
 
Embodiment 134 is a method for treating a disease in a subject in need thereof, comprising:
 
     administering to the subject a therapeutically effective amount of each of 
     a first bacterial strain comprising a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; wherein the first bacterial strain further comprises a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin; 
     a second bacterial strain comprising a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, optionally a second degradation tag, and optionally a second reporter gene; wherein the second bacterial strain further comprises a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin; and 
     a third bacterial strain comprising a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene; wherein the third bacterial strain further comprises a third toxin system; wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Embodiment 135 is a method for treating a disease in a subject in need thereof, comprising: 
     administering to the subject a therapeutically effective amount of each of 
     a first pharmaceutical comprising a first bacterial strain comprising a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; wherein the first bacterial strain further comprises a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin; 
     a second pharmaceutical comprising a second bacterial strain comprising a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, optionally a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, a second degradation tag, and optionally a second reporter gene; wherein the second bacterial strain further comprises a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin; and 
     a third pharmaceutical comprising a third bacterial strain comprising a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene; wherein the third bacterial strain further comprises a third toxin system; wherein the third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin. 
     Embodiment 136 is a method for treating a disease in a subject in need thereof, comprising: 
     administering to the subject a therapeutically effective amount of each of 
     a first bacterial strain comprising a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further comprises a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; 
     a second bacterial strain comprising a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further comprises a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, optionally a second degradation tag, and optionally a second reporter gene; and 
     a third bacterial strain comprising a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further comprises a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Embodiment 137 is a method for treating a disease in a subject in need thereof, comprising: 
     administering to the subject a therapeutically effective amount of each of 
     a first pharmaceutical composition comprising a first bacterial strain comprising a first toxin system; wherein the first toxin system produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin, wherein the first bacterial strain optionally further comprises a first lysis plasmid and a first activator plasmid; wherein the first lysis plasmid comprises a first lysis gene, a first activatable promoter, and optionally a first reporter gene; and the first activator plasmid comprises a first activator gene, optionally a first degradation tag, and optionally a first reporter gene; 
     a second pharmaceutical composition comprising second bacterial strain comprising a second toxin system; wherein the second toxin system produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin, wherein the second bacterial strain optionally further comprises a second lysis plasmid and a second activator plasmid; wherein the second lysis plasmid comprises a second lysis gene, a second activatable promoter, and optionally a second reporter gene; and the second activator plasmid comprises a second activator gene, optionally a second degradation tag, and optionally a second reporter gene; and 
     a third pharmaceutical composition comprising a third bacterial strain comprising a third toxin system produces a third toxin/third antitoxin pair and a second antitoxin from a second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, wherein the third bacterial strain optionally further comprises a third lysis plasmid and a third activator plasmid; wherein the third lysis plasmid comprises a third lysis gene, a third activatable promoter, and optionally a third reporter gene; and the third activator plasmid comprises a third activator gene, optionally a third degradation tag, and optionally a third reporter gene. 
     Embodiment 138 is the method of any one of embodiments 134-137, wherein administering comprises administering sequentially each of the first, second, and third bacterial strains or first second and third pharmaceutical compositions to the subject.
 
Embodiment 139 is the method of embodiment 138, wherein administering comprises administering each of the first, second, and third pharmaceutical compositions simultaneously and wherein each of the first, second, and third pharmaceutical compositions has a different release profile for releasing the first second and third bacterial strains.
 
Embodiment 140 is the method of any one of embodiments 134-139, wherein each of the first, second, and third bacterial strains expresses a different therapeutic agent.
 
Embodiment 141 is a method for treating a disease in a subject in need thereof, comprising:
 
     administering to the subject a therapeutically effective amount of each of n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 142 is a method for treating a disease in a subject in need thereof, comprising: 
     administering to the subject a therapeutically effective amount of each of n bacterial strains comprising at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises
         a lysis plasmid having a lysis gene under the control of an activatable promoter; and   an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule,       

     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the lysis plasmid of each of then bacterial strains comprises a toxin system; 
     wherein the toxin system of the lysis plasmid of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the lysis plasmid of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 143 is the method of embodiment 141 or embodiment 142, where n is 3.
 
Embodiment 144 is the method of embodiment 141 or embodiment 142, wherein n is 4, 5, 6, 7, 8, 9, or 10.
 
Embodiment 145 is a method for treating a disease in a subject in need thereof, comprising:
 
     administering to the subject a therapeutically effective amount of each of m pharmaceutical compositions, each comprising at least one of n bacterial strains, wherein the n bacterial strains comprise at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises a toxin system; 
     wherein the toxin system of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 146 is a method for treating a disease in a subject in need thereof, comprising: 
     administering to the subject a therapeutically effective amount of each of m pharmaceutical compositions, each comprising at least one of n bacterial strains, wherein the n bacterial strains comprise at least a first bacterial strain, a second bacterial strain, and an nth bacterial strain; 
     wherein each of the second bacterial strain to the n th  bacterial strain has a previous bacterial strain; 
     wherein n is at least 3; 
     wherein each of the n strains comprises
         a lysis plasmid having a lysis gene under the control of an activatable promoter; and   an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule,       

     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the lysis plasmid of each of then bacterial strains comprises a toxin system; 
     wherein the toxin system of the lysis plasmid of each of the second through n th  bacterial strain independently produces a first toxin/first antitoxin pair, wherein the first toxin is effective against the previous bacterial strain, and a second antitoxin from a second toxin/second antitoxin pair produced by the previous bacterial strain; 
     wherein the toxin system of the lysis plasmid of the first bacterial strain produces a third toxin/third antitoxin pair, wherein the third toxin is effective against the nth bacterial strain, and a fourth antitoxin from a fourth toxin/antitoxin pair produced by the n th  bacterial strain. 
     Embodiment 147 is the method of embodiment 145 or embodiment 146, where n is 3.
 
Embodiment 148 is the method of embodiment 145 or embodiment 146, wherein n is 4, 5, 6, 7, 8, 9, or 10.
 
Embodiment 149 is the method of any one of embodiments 145-146, wherein m=n.
 
Embodiment 150 is the method of any one of embodiments 141-149, wherein each of the toxin systems are independently encoded in the genome, on a plasmid, on multiple plasmids, or a combination thereof.
 
Embodiment 151 is the method of any one of embodiments 141-150, wherein each of the second bacterial strain through the nth bacterial strain does not produce the second toxin of the toxin system of the previous strain, and the first bacterial strain does not produce the fourth toxin of the toxin system of the nth bacterial strain.
 
Embodiment 152 is the method of any one of embodiments 145-151, wherein administering comprises administering sequentially each of the n bacterial strains or m pharmaceutical compositions to the subject.
 
Embodiment 153 is the method of embodiment 152, wherein administering comprises administering each of the m pharmaceutical compositions simultaneously and wherein each of the m pharmaceutical compositions has a different release profile for releasing the first second and third bacterial strains.
 
Embodiment 154 is the method of any one of embodiments 141-153, wherein each of the first, second, and third bacterial strains expresses a different therapeutic agent.
 
Embodiment 155 is the method of any one of embodiments 141-154, wherein the disease is cancer or an infection.
 
Embodiment 156 is the method of embodiment 155, wherein the infection is caused by an infectious agent selected from the group consisting of:  Camphylobacter jejuni, Clostridium botulinium, Escherichia coli, Listeria monocytogenes  and  Salmonella.  
 
Embodiment 157 is the method of embodiment 155, wherein the cancer is selected from the group consisting of: glioblastoma, squamous cell carcinoma, breast cancer, colon cancer, hepatocellular cancer, melanoma, neuroblastoma, pancreatic cancer, and prostate cancer.
 
Embodiment 158 is the method of any one of embodiments 1-83 or 134-157, the bacterial strain of any one of embodiments 84-111, the pharmaceutical compositions of any one of embodiments 112-113, the systems of any one of embodiments 114-123, 132, or 133, or the kits of any one of embodiments 124-131, wherein one or more of the bacterial strains expresses a therapeutic agent.
 
Embodiment 159 is the method of any one of embodiments 1-83 or 134-157, the bacterial strain of any one of embodiments 84-111, the pharmaceutical compositions of any one of embodiments 112-113, the systems of any one of embodiments 114-123, 132, or 133, or the kits of any one of embodiments 124-131, wherein one or more of the bacterial strains expresses a therapeutic agent selected from the group consisting of: an inhibitory nucleic acid, a cytokine, an enzyme, a peptide hormone, a fusion protein, a clotting factor, a toxin, an antimicrobial peptide, and an antibody or antigen-binding fragment thereof.
 
Embodiment 160 is a method comprising:
 
     culturing a first bacterial strain for a first period of time in a growth environment; 
     adding a second bacterial strain to the growth environment and culturing the second bacterial strain for a second period of time; 
     adding a third bacterial strain to the growth environment and culturing the third bacterial strain for a second period of time, 
     wherein each of the first, second, and third bacterial strains comprises a toxin system; 
     wherein the toxin system of the first bacterial strain produces a first toxin/first antitoxin pair and a third antitoxin from a third toxin/third antitoxin pair wherein the first bacterial strain does not produce the third toxin; 
     wherein the toxin system of the second bacterial strain produces a second toxin/second antitoxin pair and the first antitoxin from the first toxin/first antitoxin pair wherein the second bacterial strain does not produce the first toxin; and 
     wherein the toxin system of the third bacterial strain produces a third toxin/third antitoxin pair and the second antitoxin from the second toxin/second antitoxin pair wherein the third bacterial strain does not produce the second toxin, 
     wherein the toxin system is encoded on a plasmid, multiple plasmids, integrated into the host genome, or a combination thereof. 
     Embodiment 161 is the method of embodiment 160, wherein each of the first, second, and third bacterial strains comprises: 
     a lysis plasmid having a lysis gene under the control of an activatable promoter; and 
     an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, 
     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the quorum sensing molecule may or may not be different in each of the first, second, and third bacterial strains; 
     wherein each quorum-sensing molecule of each of the first, second, and third bacterial strains may or may not have any effect on the activatable promoter of the lysis gene of another strain. 
     Embodiment 162 is the method of embodiment 161, wherein each of the lysis plasmids of the first, second, and third bacterial strains is the plasmid containing the toxin system for such bacterial strain, or wherein each of the activator plasmids of the first, second, and third bacterial strains is the plasmid containing the toxin system for such bacterial strain, or wherein the toxin system for each bacterial strain is integrated into the genome.
 
Embodiment 163 is a method of culturing n bacterial strains comprising:
 
     culturing a first bacterial strain of n bacterial strains for a first period of time in a culture; 
     adding a second bacterial strain of the n bacterial strains to the culture and culturing the second bacterial strain for a second period of time; 
     adding each of the other of the n bacterial strains to the culture and culturing each such bacterial strain for a period of time, 
     wherein n is three or a greater whole number and 
     wherein a plasmid of each of the n bacterial strains comprises a toxin system; 
     wherein the toxin system of the plasmid of the first bacterial strain produces a first toxin/first antitoxin pair and a nth antitoxin from an nth toxin/nth antitoxin pair wherein the first bacterial strain does not produce the nth toxin; 
     wherein the toxin system of the plasmid of each mth, where m is an element of the set {2, 3, . . . , n}, of the other bacterial strains in the n bacterial strains produces a mth toxin/mth antitoxin pair and the (m−1)th antitoxin from the (m−1)th toxin/(m−1)th antitoxin pair. 
     Embodiment 164 is the method of embodiment 163, wherein each of the n bacterial strains comprises: 
     a lysis plasmid having a lysis gene under the control of an activatable promoter; and 
     an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, 
     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the quorum sensing molecule may or may not be different in each of the n bacterial strains; 
     wherein each quorum-sensing molecule of each of the n bacterial strains may or may not have an effect on the activatable promoter of the lysis gene of another strain of the n bacterial strains. 
     Embodiment 165 is the method of embodiment 164, wherein each of the lysis plasmids of the n strains is the plasmid containing the toxin system for such bacterial strain.
 
Embodiment 166 is the method of any one of embodiments 163-164, wherein each of the n bacterial strains produces a payload.
 
Embodiment 167 is the method of any one of embodiments 163-165, wherein each of the n bacterial strains produces a different payload.
 
Embodiment 168 is the method of any one of embodiments 163-165, wherein each of the n bacterial strains produces the same payload.
 
Embodiment 169 is the method of any one of embodiments 166-168, wherein each payload is a therapeutic.
 
Embodiment 170 is the method of embodiment 167, wherein the payload of the mth bacterial strain produces an mth substrate by directly or indirectly acting upon the substrate of the (m−1)th bacterial strain, and wherein the payload of the first bacterial strain acts upon a substrate present in the environment where the n bacterial strains are cultured.
 
Embodiment 171 is the method of any one of embodiments 163-170, wherein n is four.
 
Embodiment 172 is the method of any one of embodiments 163-170, wherein n is five.
 
Embodiment 173 is the method of any one of embodiments 163-170, wherein n is six.
 
Embodiment 174 is the method of any one of embodiments 160-162, further comprising culturing or co-culturing one or more additional bacterial strains in the culture.
 
Embodiment 175 is the method of embodiment 174, wherein each of the one or more additional bacterial strains comprise:
 
     a lysis plasmid having a lysis gene under the control of an activatable promoter; and 
     an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, 
     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the quorum sensing molecule is different in each of the first, second, third, and one or more additional bacterial strains; 
     wherein each quorum-sensing molecule of each of the first, second, third, and one or more additional bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another bacterial strain used in the culture. 
     Embodiment 176 is the method of embodiment 175, wherein the lysis plasmid of each of the one or more additional bacterial strains comprises a toxin system.
 
Embodiment 177 is the method of any one of embodiments 160-162 or 174-176, wherein the lysis plasmid and activator plasmid of each of the at least first, second, and third bacterial strains is the same plasmid.
 
Embodiment 178 is the method of any one of embodiments 160-162 or 174-176, wherein the lysis plasmid and activator plasmid of each of the at least the first, second, and third bacterial strains are separate plasmids.
 
Embodiment 179 is the method of any one of embodiments 160-162 or 174-178, wherein at least the first, second, and third bacterial strains are metabolically competitive.
 
Embodiment 180 is the method of any one of embodiments 160-162 or 174-179, wherein at least the first, second, and third bacterial strains are selected from  E. coli, S. typhimurium , or a bacterial variant thereof.
 
Embodiment 181 is the method of any one of embodiments 160-162 or 174-180, wherein each of the at least the first, second, and third bacterial strains does not have a growth advantage compared to another strain in the culture.
 
Embodiment 182 is the method of any one of embodiments 160-162 or 174-181, wherein in each of the at least the first, second, and third bacterial strains the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, a degradation tag, and optionally a reporter gene.
 
Embodiment 183 is the method of any one of embodiments 160-162 or 174-182, wherein the lysis gene in each of the at least the first, second, and third bacterial strains is E from a bacteriophage ΦX174.
 
Embodiment 184 is the method of any one of embodiments 160-162 or 174-183, wherein the activatable promoter in each of the at least the first, second, and third bacterial strains is a LuxR-AHL activatable luxI promoter and the activator gene is a LuxI.
 
Embodiment 185 is the method of embodiment 182, wherein at least one reporter gene is selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof.
 
Embodiment 186 is the method of embodiment 182, wherein the degradation tag is an ssrA-LAA degradation tag.
 
Embodiment 187 is the method of any one of embodiments 160-162 or 174-186, wherein at least one of the plasmids is integrated into a genome of at least one of the first, second, and third bacterial strains.
 
Embodiment 188 is the method of any one of embodiments 160-162 or 174-187, wherein the culturing occurs in a designated growth environment.
 
Embodiment 189 is the method of any one of embodiments 160-162 or 174-188, wherein the culturing occurs in a microfluidic device.
 
Embodiment 190 is the method of any one of embodiments 160-162 or 174-188, wherein the culturing occurs in a bio reactor.
 
Embodiment 191 is the method of any one of embodiments 160-162 or 174-188, wherein the culturing occurs in in vivo.
 
Embodiment 192 is the method of any one of embodiments 160-191, wherein each of the bacterial strains produce therapeutic payloads and the culturing occurs in a human or animal patient in need of the therapeutic payloads.
 
Embodiment 193 is the method of any one of embodiments 160-162 or 174-191, wherein each of the first, second, and third periods of time ranges from about 12 to about 72 hours.
 
Embodiment 194 is the method of any one of embodiments 160-162, 174-191, or 193, wherein each of the first, second, and third periods of time ranges from about 1 hours to about n hours.
 
Embodiment 195 is the method of any one of embodiments 160-162, 174-191, or 193, wherein each of the first, second, and third periods of time is selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours.
 
Embodiment 196 is the method of any one of embodiments 163-173, wherein each of the n periods of time partially or completely overlap.
 
Embodiment 197 is the method of any one of embodiments 163-173 or 196, wherein the n bacterial strains are cultured together.
 
Embodiment 198 is the method of any one of embodiments 163-173, 196, or 197, wherein each of the n bacterial strains are added to the culture sequentially such that each mth bacterial strain is added to the culture after the passage of the (m−1)th period of time.
 
Embodiment 199 is the method of any one of embodiments 160-162, 174-191, or 193-195, wherein each of the first, second, and third periods of time is selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours.
 
Embodiment 200 is a method of maintaining a co-culture, the method comprising:
 
     co-culturing at least three bacterial strains; 
     wherein each of the at least three bacterial strains comprises a lysis plasmid having a lysis gene under the control of an activatable promoter; and 
     an activator plasmid having an activator gene, the expression of which promotes the accumulation of a quorum sensing molecule, 
     wherein both the activatable promoter of the lysis gene and the expression of the activator gene is activated by the quorum sensing molecule, 
     wherein the quorum sensing molecule is different in each of the at least three bacterial strains; 
     wherein each quorum-sensing molecule of each of the at least three bacterial strains has no or substantially no effect on the activatable promoter of the lysis gene of another strain;
         wherein the lysis plasmid comprises a toxin/antitoxin system.
 
Embodiment 201 is the method of embodiment 200, wherein the toxin/antitoxin system produces a toxin/antitoxin pair and a different antitoxin of another strain.
 
Embodiment 202 is the method of embodiment 200 or 201, wherein the lysis plasmid and activator plasmid of each of the at least three bacterial strains is the same plasmid.
 
Embodiment 203 is the method of any one of embodiments 200-202, wherein the lysis plasmid and activator plasmid of each of the at least three bacterial strains are separate plasmids.
 
Embodiment 204 is the method of any one of embodiments 200-203, wherein the at least the three strains are metabolically competitive.
 
Embodiment 205 is the method of any one of embodiments 200-204, wherein the at least three strains are selected from  E. coli, S. typhimurium , or a bacterial variant thereof.
 
Embodiment 206 is the method of any one of embodiments 200-205, wherein each of the at least three strains does not have a growth advantage compared to another strain.
 
Embodiment 207 is the method of any one of embodiments 200-206, wherein in each of the at least three strains the lysis plasmid comprises a lysis gene, an activatable promoter, and optionally a reporter gene; and the activator plasmid comprises an activator gene, optionally a degradation tag, and optionally a reporter gene.
 
Embodiment 208 is the method of any one of embodiments 200-207, wherein the lysis gene in the at least three strains is E from a bacteriophage ΦX174.
 
Embodiment 209 is the method of any one of embodiments 200-208, wherein the activatable promoter is a LuxR-AHL activatable luxI promoter and the activator gene is a LuxI.
 
Embodiment 210 is the method of embodiment 207, wherein at least one reporter gene is selected from a gene encoding a green fluorescent protein (GFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), or a variant thereof.
 
Embodiment 211 is the method of embodiment 207, wherein the degradation tag is an ssrA-LAA degradation tag.
 
Embodiment 212 is the method of any one of embodiments 200-211, wherein the co-culture is inoculated at a ratio of 1:1:1 of each of the at least three bacterial strains.
 
Embodiment 213 is the method of any one of embodiments 200-212, wherein at least one of the plasmids is integrated into a genome of at least one of the at least three strains.
 
Embodiment 214 is the method of any one of embodiments 200-213, wherein the culturing occurs in a microfluidic device.
 
Embodiment 215 is the method of any one of embodiments 200-214, wherein the period of time is 12 to 72 hours.
 
Embodiment 216 is the method of any one of embodiments 200-214, wherein the period of time is selected from at least 24 hours, at least 48 hours, at least 72 hours, and at least 96 hours.
 
Embodiment 217 is the method of any one of embodiments 200-214, wherein the period of time is selected from 12 hours, 24 hours, 48 hours, 72 hours, and 96 hours.
 
Embodiment 218 is the method of any one of embodiments 200-217, wherein the co-culturing of the at least three strains is in a constant lysis state; wherein the constant lysis state is characterized by a steady-state balance of growth and lysis of the at least three bacterial strains.
       

     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.