Patent Publication Number: US-10788452-B2

Title: High resolution systems, kits, apparatus, and methods for bacterial community relationship determination and other high throughput microbiology applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Nonprovisional patent application Ser. No. 15/135,377, filed on Apr. 21, 2016, which claims the benefit of U.S. Provisional Patent Application No. 62/299,088 filed Feb. 24, 2016, U.S. Provisional Patent Application No. 62/292,091 filed Feb. 5, 2016, and U.S. Provisional Patent Application No. 62/150,677 filed Apr. 21, 2015. This application also claims the benefit of U.S. Provisional Patent Application No. 62/400,841 filed on Sep. 28, 2016. The disclosure of each of these prior-filed applications is incorporated by reference herein in its entirety. 
    
    
     INCORPORATION OF SEQUENCE LISTING 
     This application includes a Sequence Listing which is being submitted in ASCII format via EFS-Web, named “GALT_007_US_ST25.txt,” which is 3 KB in size and created on Sep. 27, 2017. The contents of the Sequence Listing are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present disclosure relates generally to innovations in microbiology, microfabrication, chemistry, optics, robotics, and information technology. More specifically, the present disclosure relates to systems, apparatus, kits, and methods for high throughput cultivation, screening, isolation, sampling, and/or identification of biological entities and/or nutrients. 
     BACKGROUND 
     Traditional techniques and tools for cultivating biological entities from environmental and other samples are often slow, laborious, and expensive. Even with these techniques and tools, often cells and other biological entities still defy all attempts at culture, resulting in missed information and/or product opportunities. Likewise, the screening of a population of biological entities for a particular metabolite, enzyme, protein, nucleic acid, phenotype, mutation, metabolic pathway, gene, adaptation, capability, and/or therapeutic benefit is challenging, requiring complex and expensive methods. For example, microbes live in extremely high-risk environments. To survive, microbes have developed amazing sets of biochemical tools, including novel enzymes, unique metabolites, innovative genetic pathways, and strategies for manipulating their environment and their microbial neighbors—powerful solutions that could lead to new insights and products ranging from life-saving antibiotics to fertilizers that improve food production and security. 
     SUMMARY 
     The present disclosure provides microbiology systems, apparatus, kits, and methods for streamlining the cultivation workflow, supporting high throughput screening, and/or developing new insights and products in accordance with some embodiments. 
     In some embodiments, a method of analyzing a sample including a population of biological entities is provided. The methods employs at least one microfabricated device having a top surface defining (or comprising) an array of microwells, wherein a plurality of the microwells of the array of microwells each comprise a unique tag nucleic acid molecule including: (1) a target-specific nucleotide sequence for annealing to a target nucleic acid fragment of one or more biological entities of interest that may be present in the microwell, and (2) a location-specific nucleotide sequence for identifying the location of the microwell on the microfabricated device. The method comprises: loading a sample onto the microfabricated device such that at least some microwells of the plurality of microwells each include more than one cell of a biological entity as well as an amount of a nutrient; incubating the microfabricated device at predetermined conditions; amplifying, in individual microwells, a selected genetic material of the cells (e.g., genomic DNA of the cells) of the biological entities obtained from the incubation in the plurality of microwells, thereby obtaining first amplicons in at least a subset of the plurality of microwells; sequencing an aggregate of the first amplicons collected from the subset the plurality of microwells to obtain sequencing data; and based on the sequencing data and the unique tag nucleic molecule included in each of the plurality of microwells, obtaining an identification of the biological entities present in each of the subset of the plurality of microwells of the at least one microfabricated device. 
     In some embodiments of the method, based on the identification of the biological entities present in each of the subset of the plurality of microwells, a presence or absence of a relationship between at least two different types of biological entities in the population of biological entities contained in the sample is determined. The relationship can be one of a dependent relationship, a symbiotic relationship, or a destructive relationship. In some embodiments, the presence or absence of a relationship can be determined by comparing across the plurality of microwells which types of biological entities are present or not present in the same microwells after incubation. 
     In some embodiments of the method, loading the sample onto the microfabricated device can be performed such that each microwell of the plurality of microwells includes, on average, N cells of any biological entity (the N cells can be same type or different types), where N is a number and equal to 2 or greater. For example, N can be a number between 2 and 100, between 2 and 50, between 2 and 20, between 2 and 10, etc. 
     In some embodiments of the method, the biological entities in the sample comprise bacteria. The bacteria can include bacteria of different strains, different species, or different genera. The population of the of the population of the biological entities in the sample can include a collection of microorganisms naturally occurring in a specific environment. For example, the biological entities can be a collection of microorganisms obtained from human stool, human gut, human skin, human nasal cavity, vagina, soil, rhizosphere, water, etc. In other embodiments, the biological entities in the sample can include viruses, fungi, or eukaryotic cells. 
     In some embodiments of the method, prior to incubation, a membrane can be applied on the top surface of the microfabricated device to retain the biological entities loaded in the plurality of microwells. The nutrient can be pre-loaded in the microwells and retained by the membrane. The nutrient can include a plurality of different nutrients loaded across the microwells of the at least one microfabricated device. In such a case, determining the determining the presence or absence of a relationship between at least two types of biological entities can include determining such a relationship dependent on the different nutrients. In some embodiments, the nutrient can be included in a reservoir provided on the membrane and external to the microwells. In such a case, the membrane can be permeable to the nutrient and allows the nutrient to migrate from the reservoir into the microwells through the membrane. 
     In some embodiments, the method further comprises transferring at least some of the cells of the biological entities obtained from the incubation to a target location. In such a case, the amplifying and sequencing can be performed on either the cells not transferred to the target location or the cells transferred to the target location. 
     In some embodiments, the unique tag nucleic acid molecule in each of the plurality of microwells constitutes a portion of a PCR primer used in the amplification. 
     In some embodiments, the surface density of the arrays of microwells of the at least one microfabricated device can be at least 150 microwells per cm 2 , at least 250 microwells per cm 2 , at least 400 microwells per cm 2 , at least 500 microwells per cm 2 , at least 750 microwells per cm 2 , at least 1,000 microwells per cm 2 , at least 2,500 microwells per cm 2 , at least 5,000 microwells per cm 2 , at least 7,500 microwells per cm 2 , at least 10,000 microwells per cm 2 , at least 50,000 microwells per cm 2 , at least 100,000 microwells per cm 2 , or at least 160,000 per cm 2 . In some embodiments, each microwell of the arrays of microwells of the at least one microfabricated device can have a diameter of from about 5 μm to about 500 μm, from about 10 μm to about 300 μm, or from about 20 μm to about 200 μm. 
     In some embodiments, a method of analyzing a sample including a population of biological entities using at least one microfabricated device having a top surface defining an array of microwells is provided. The method comprises: loading into each of a plurality of the microwells of the array of microwells with a unique tag nucleic acid molecule including: (1) a target-specific nucleotide sequence for annealing to a target nucleic acid fragment of one or more biological entities of interest that may be present in the microwell, and (2) a location-specific nucleotide sequence for identifying the location of the microwell on the at least microfabricated device; loading a sample onto the microfabricated device such that at least some microwells of the plurality of microwells each includes more than one cell of a biological entity as well as an amount of a nutrient; incubating the microfabricated device at predetermined conditions; amplifying a selected genetic material of the cells of the biological entities obtained from the incubation in at least a subset of the plurality of microwells of the at least one microfabricated device, thereby obtaining first amplicons in the plurality of microwells; sequencing an aggregate of the first amplicons collected from the subset the plurality of microwells to obtain sequencing data; and based on the sequencing data and the unique tag nucleic molecule included in each of the plurality of microwells, obtaining an identification of the biological entities present in each of the subset of the plurality of microwells of the at least one microfabricated device. 
     In some embodiments, a method of analyzing a microbiome of microorganisms collected from a specific environment is provided. The method employs at least one microfabricated device having a top surface defining an array of microwells, wherein a plurality of the microwells of the array of microwells each comprise a unique tag nucleic acid molecule including: (1) a target-specific nucleotide sequence for annealing to a target nucleic acid fragment of one or more biological entities of interest that may be present in the microwell, and (2) a location-specific nucleotide sequence for identifying the location of the microwell on the microfabricated device. The method includes: loading a sample prepared from the microbiome onto the at least one microfabricated device such that the plurality of microwells each include, on average, 2 to 20 cells of any microorganism of the microbiome as well as an amount of a nutrient; incubating the microfabricated device at predetermined conditions; amplifying a selected genetic material of the microorganisms obtained from the incubation in at least a subset of the plurality of microwells in the at least one microfabricated device, thereby obtaining first amplicons in the plurality of microwells; sequencing an aggregate of first amplicons collected from the subset of the plurality of microwells to obtain sequencing data; and based on the sequencing data and the unique tag nucleic molecule included in each of the plurality of microwells, obtaining an identification of microorganisms present in each of the subset of the plurality of microwells of the at least one microfabricated device; and based on the identification of the microorganisms present in the plurality of microwells, determining a presence or absence of a relationship between at least two different types of microorganisms in the microbiome. 
     In some embodiments, a method of analyzing a relationship among microorganisms of a microbiome collected from a specific environment is provided. The method comprises: partitioning microorganisms of the microbiome into a plurality of portions each including, on average, 2 to 20 cells of any microorganism of the microbiome; incubating each portion of the plurality of portions of microorganisms in a separate compartment at predetermined conditions in the presence of a nutrient; identifying the microorganisms present in each of at least a subset of the isolated compartments after incubation; and determining a presence or absence of a relationship between at least two different types of the microorganisms in the microbiome based on a comparison across the subset of compartments which types of microorganisms as identified are present or not present in the same microwells. 
     It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein. 
     Other systems, processes, and features will become apparent to those skilled in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, processes, and features be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements). 
         FIG. 1  is a perspective view illustrating a microfabricated device or chip in accordance with some embodiments. 
         FIGS. 2A-2C  are top, side, and end views, respectively, illustrating dimensions of microfabricated device or chip in accordance with some embodiments. 
         FIGS. 3A and 3B  are exploded and top views, respectively, illustrating a microfabricated device or chip in accordance with some embodiments. 
         FIGS. 4A and 4B  are diagrams illustrating a membrane in accordance with some embodiments.  FIG. 4C  is an image of a membrane surface with impressions formed from contact with an array of wells in accordance with some embodiments. 
         FIG. 5A  is a flowchart illustrating a method for isolating cells from a sample in accordance with some embodiments.  FIG. 5B  is a diagram illustrating a method for isolating cells from a soil sample in accordance with some embodiments. 
         FIG. 6  is a flowchart illustrating a method for isolating and cultivating cells from a sample in accordance with some embodiments. 
         FIG. 7  is a diagram illustrating a method for isolating and cultivating cells from a complex sample in accordance with some embodiments. Panel  716  shows the output: isolated strains of cultivated cells (SEQ ID NOs: 2-6). 
         FIGS. 8A-8C  are diagrams illustrating picking by one pin or multiple pins in accordance with some embodiments. 
         FIGS. 9A-9D  are images demonstrating picking of a well in accordance with some embodiments. 
         FIGS. 10A-10D  are diagrams illustrating a tool for picking a chip in accordance with some embodiments. 
         FIG. 11  is an image of a well that has been picked through a thin layer of agar, illustrating picking through a membrane or sealing layer in accordance with some embodiments. 
         FIG. 12  is a diagram illustrating a cross-section of a chip  1200  in accordance with some embodiments. 
         FIG. 13  is a flowchart illustrating methods for screening in accordance with some embodiments. 
         FIG. 14  is a diagram illustrating a screening method in accordance with some embodiments. 
         FIG. 15  is a series of images illustrating a screening example in accordance with some embodiments. 
         FIGS. 16A-16C  are images illustrating recovery from a screen in accordance with some embodiments. 
         FIG. 17A  is an exploded diagram illustrating a chip for screening in accordance with some embodiments.  FIG. 17B  is a fluorescence image of a chip following screening in accordance with some embodiments.  FIG. 17C  is an image showing a process of picking a sample from the chip following screening in accordance with some embodiments. 
         FIG. 18  is a flowchart illustrating a counting method in accordance with some embodiments. 
         FIG. 19  is a diagram illustrating a counting method in accordance with some embodiments. Panel  1916  shows the output: sequences and relative abundance of cultivated cells (SEQ ID NOs: 2-6). 
         FIG. 20  is a diagram illustrating an indexing system in accordance with some embodiments. 
         FIGS. 21A-21E  are diagrams illustrating a chip with well-specific chemistries in accordance with some embodiments. 
         FIG. 22  is a diagram showing a summary of the number of genera of bacteria in the microwells of a microfabricated device in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to systems, kits, apparatus, and methods for isolation, culturing, adaptation, sampling, and/or screening of biological entities and/or nutrients. A microfabricated device (or a “chip”) is disclosed for receiving a sample comprising at least one biological entity (e.g., at least one cell). The term “biological entity” may include, but is not limited to, an organism, a cell, a cell component, a cell product, and a virus, and the term “species” may be used to describe a unit of classification, including, but not limited to, an operational taxonomic unit (OTU), a genotype, a phylotype, a phenotype, an ecotype, a history, a behavior or interaction, a product, a variant, and an evolutionarily significant unit. 
     A cell may be Archaea, Bacteria, or Eukaryota (e.g., fungi), mammalian cells, etc. For example, a cell may be a microorganism, such as an aerobic, anaerobic, or facultative aerobic microorganisms. A virus may be a bacteriophage. Other cell components/products may include, but are not limited to, proteins, amino acids, enzymes, saccharides, adenosine triphosphate (ATP), lipids, nucleic acids (e.g., DNA and RNA), nucleosides, nucleotides, cell membranes/walls, flagella, fimbriae, organelles, metabolites, vitamins, hormones, neurotransmitters, and antibodies. 
     A nutrient may be defined (e.g., a chemically defined or synthetic medium) or undefined (e.g., a basal or complex medium). A nutrient may include or be a component of a laboratory-formulated and/or a commercially manufactured medium (e.g., a mix of two or more chemicals). A nutrient may include or be a component of a liquid nutrient medium (i.e., a nutrient broth), such as a marine broth, a lysogeny broth (e.g., Luria broth), etc. A nutrient may include or be a component of a liquid medium mixed with agar to form a solid medium and/or a commercially available manufactured agar plate, such as blood agar. 
     A nutrient may include or be a component of selective media. For example, selective media may be used for the growth of only certain biological entities or only biological entities with certain properties (e.g., antibiotic resistance or synthesis of a certain metabolite). A nutrient may include or be a component of differential media to distinguish one type of biological entity from another type of biological entity or other types of biological entities by using biochemical characteristics in the presence of specific indicator (e.g., neutral red, phenol red, eosin y, or methylene blue). 
     A nutrient may include or be a component of an extract of or media derived from a natural environment. For example, a nutrient may be derived from an environment natural to a particular type of biological entity, a different environment, or a plurality of environments. The environment may include, but is not limited to, one or more of a biological tissue (e.g., connective, muscle, nervous, epithelial, plant epidermis, vascular, ground, etc.), a biological fluid or other biological product (e.g., amniotic fluid, bile, blood, cerebrospinal fluid, cerumen, exudate, fecal matter, gastric fluid, interstitial fluid, intracellular fluid, lymphatic fluid, milk, mucus, rumen content, saliva, sebum, semen, sweat, urine, vaginal secretion, vomit, etc.), a microbial suspension, air (including, e.g., different gas contents), supercritical carbon dioxide, soil (including, e.g., minerals, organic matter, gases, liquids, organisms, etc.), sediment (e.g., agricultural, marine, etc.), living organic matter (e.g., plants, insects, other small organisms and microorganisms), dead organic matter, forage (e.g., grasses, legumes, silage, crop residue, etc.), a mineral, oil or oil products (e.g., animal, vegetable, petrochemical), water (e.g., naturally-sourced freshwater, drinking water, seawater, etc.), and/or sewage (e.g., sanitary, commercial, industrial, and/or agricultural wastewater and surface runoff). 
     A microfabricated device may define a high density array of microwells for cultivating the at least one biological entity. The term “high density” may refer to a capability of a system or method to distribute a number of experiments within a constant area. For example, a microfabricated device comprising a “high density” of experimental units may include about 150 microwells per cm 2  to about 160,000 microwells or more per cm 2 , as discussed further herein. Additional examples are shown in TABLE 1. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Length of side 
                 Spacing between 
                 Density of 
               
               
                 of microwells 
                 microwells 
                 microwells 
               
               
                 (μm) 
                 (μm) 
                 (wells/cm2) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 500 
                 500 
                 100 
               
               
                 100 
                 100 
                 2500 
               
               
                 100 
                 50 
                 4489 
               
               
                 100 
                 10 
                 8281 
               
               
                 50 
                 50 
                 10000 
               
               
                 50 
                 10 
                 27556 
               
               
                 20 
                 10 
                 110889 
               
               
                 10 
                 5 
                 444889 
               
               
                 5 
                 5 
                 1000000 
               
               
                   
               
            
           
         
       
     
     A microfabricated device may include a substrate with a series of functional layers. The series of functional layers may include a first functional layer defining a first array of experimental units (e.g., wells) and at least one subsequent functional layer defining a subsequent array of experimental units (e.g., microwells) in each experimental unit of the preceding functional layer. Each of the experimental units may be configured to receive and cultivate and/or screen biological entities and/or nutrients. In particular, systems, kits, apparatus, and methods described herein may be used for automated and/or high throughput screening of different conditions against a high density matrix of cells. For example, systems, kits, apparatus, and methods described herein may be used to test and compare the effect(s) of one or more different nutrients on the growth of microorganisms and/or screen for metabolites, enzyme activity, mutations, or other cell features. 
       FIG. 1  is a perspective view illustrating a microfabricated device or chip in accordance with some embodiments. Chip  100  includes a substrate shaped in a microscope slide format with injection-molded features on top surface  102 . The features include four separate microwell arrays (or microarrays)  104  as well as ejector marks  106 . The microwells in each microarray are arranged in a grid pattern with well-free margins around the edges of chip  100  and between microarrays  104 . 
       FIGS. 2A-2C  are top, side, and end views, respectively, illustrating dimensions of chip  100  in accordance with some embodiments. In  FIG. 2A , the top of chip  100  is approximately 25.5 mm by 75.5 mm. In  FIG. 2B , the end of chip  100  is approximately 25.5 mm by 0.8 mm. In  FIG. 2C , the side of chip  100  is approximately 75.5 mm by 0.8 mm. 
     After a sample is loaded on a microfabricated device, a membrane may be applied to at least a portion of a microfabricated device.  FIG. 3A  is an exploded diagram of the microfabricated device  300  shown from a top view in  FIG. 3B  in accordance with some embodiments. Device  300  includes a chip with an array of wells  302  holding, for example, soil microbes. A membrane  304  is placed on top of the array of wells  302 . A gasket  306  is placed on top of the membrane  304 . A polycarbonate cover  308  with fill holes  310  is placed on top of the gasket  306 . Finally, sealing tape  312  is applied to the cover  308 . 
     A membrane may cover at least a portion of a microfabricated device including one or more experimental units, wells, or microwells. For example, after a sample is loaded on a microfabricated device, at least one membrane may be applied to at least one microwell of a high density array of microwells. A plurality of membranes may be applied to a plurality of portions of a microfabricated device. For example, separate membranes may be applied to separate subsections of a high density array of microwells. 
     A membrane may be connected, attached, partially attached, affixed, sealed, and/or partially sealed to a microfabricated device to retain at least one biological entity in the at least one microwell of the high density array of microwells. For example, a membrane may be reversibly affixed to a microfabricated device using lamination. A membrane may be punctured, peeled back, detached, partially detached, removed, and/or partially removed to access at least one biological entity in the at least one microwell of the high density array of microwells. 
     A portion of the population of cells in at least one experimental unit, well, or microwell may attach to a membrane (via, e.g., adsorption). If so, the population of cells in at least one experimental unit, well, or microwell may be sampled by peeling back the membrane such that the portion of the population of cells in the at least one experimental unit, well, or microwell remains attached to the membrane. 
       FIGS. 4A and 4B  are diagrams illustrating a membrane in accordance with some embodiments.  FIG. 4A  shows a side view of a chip  400  defining an array of wells filled with content and a membrane  402  sealed on chip  400  over the array of wells, such that the surface of membrane  402  that was in contact with chip  400 , when peeled off chip  400 , has impressions of each of the wells with samples of the well contents attached (e.g., stuck) thereto, as shown in  FIG. 4B .  FIG. 4C  is an image of a membrane surface with impressions formed from contact with an array of wells in accordance with some embodiments. 
     A membrane may be impermeable, semi-permeable, selectively permeable, differentially permeable, and/or partially permeable to allow diffusion of at least one nutrient into the at least one microwell of a high density array of microwells. For example, a membrane may include a natural material and/or a synthetic material. A membrane may include a hydrogel layer and/or filter paper. In some embodiments, a membrane is selected with a pore size small enough to retain at least some or all of the cells in a microwell. For mammalian cells, the pore size may be a few microns and still retain the cells. However, in some embodiments, the pore size may be less than or equal to about 0.2 μm, such as 0.1 μm. Membrane diameters and pore sizes depend on the material. For example, a hydrophilic polycarbonate membrane may be utilized, for which the diameter may range from about 10 mm to about 3000 mm, and the pore size may range from about 0.01 μm to about 30.0 μm. An impermeable membrane has a pore size approaching zero. In embodiments with an impermeable membrane, any nutrients must be provided in a microwell prior to being sealed with the membrane. A membrane that is gas permeable but not liquid permeable may allow oxygen into a microwell and carbon dioxide out of the microwell. The membrane may have a complex structure that may or may not have defined pore sizes. However, the pores may be on a nanometer scale. Other factors in selecting a membrane may include cost, ability to seal, and/or ability to sterilize. 
     A substrate may define an array of microchannels extended from a first surface to a second surface opposite the first surface. A microchannel may have a first opening in the first surface and a second opening in the second surface. A first membrane may be applied to at least a portion of the first surface such that at least some of the population of cells in at least one microchannel attach to the first membrane. A second detachable membrane may be applied to at least a portion of the second surface such that at least some of the population of cells in at least one microchannel attach to the second membrane. The population of cells in the at least one microchannel is sampled by peeling back the first membrane such that the at least some of the population of cells in the at least one microchannel remain attached to the first membrane and/or the second membrane such that the at least some of the population of cells in the at least one microchannel remain attached to the second membrane. 
     The term “high throughput” may refer to a capability of a system or method to enable quick performance of a very large number of experiments in parallel or in series. An example of a “high throughput” system may include automation equipment with cell biology techniques to prepare, incubate, and/or conduct a large number of chemical, genetic, pharmacological, optical, and/or imaging analyses to screen one or more biological entities for at least one of a metabolite, an enzyme, a protein, a nucleic acid, a phenotype, a mutation, a metabolic pathway, a gene, an adaptation, and a capability, as discussed herein. According to some embodiments, “high throughput” may refer to simultaneous or near simultaneous experiments on a scale ranging from at least about 96 experiments to at least about 10,000,000 experiments. 
     Systems, kits, apparatus, and methods disclosed herein may be used for high throughput screening of different conditions against a matrix of biological entities (e.g., cells). A “wells-within-wells” concept may be implemented by manufacturing (e.g., microfabricating) a substrate or chip to have multiple levels of functional layers to whatever level is required or desired (i.e., wells within wells within wells within wells, etc.). A first functional layer may define an array of experimental units (e.g., wells). Each of the experimental units presents a second functional layer by defining a subsequent array of experimental units (e.g., microwells). This enables multiple experiments or tests to be performed at the same time on a single chip, thus enabling high throughput operation. 
     For example, in  FIGS. 3A and 3B , gasket  306  is placed on top of membrane  304 , which is applied to an array of wells  302  on a microfabricated device  300  in accordance with some embodiments. Gasket  306  has only one opening. However, in further embodiments, multiple smaller gaskets with a smaller opening or a single gasket with more than one smaller opening may be placed on top of a device (either with or without a membrane), thereby forming a functional layer or an array of larger experimental units with a subsequent functional layer or subsequent array of experimental units (e.g., wells  302 ) located therein. 
     With multiple levels of functional layers, more than one nutrient or nutrient formulation, for example, can be tested simultaneously or near simultaneously. The same format may be used, for example, to screen for metabolites or specific capabilities of cells or to wean microorganisms from environmentally derived nutrients to other nutrients. 
     Experimental units are predetermined sites on a surface of a microfabricated device. For example, a surface of a chip may be designed to immobilize cells in a first array of predetermined sites. These predetermined sites may be wells, microwells, microchannels, and/or designated immobilization sites. For example, a surface may be manufactured to define an array of microwells. The array may be divided into sections by defining walls in the substrate or adding walls. For example, the surface may be manufactured to first define a first array of wells, in which an inner surface of each well, in turn, is manufactured to define a second array of microwells, microchannels, or immobilization sites. In another example, the surface may be manufactured to define an array of microwells, and another substrate (e.g., agar, plastic, or another material) is applied to the surface to partition the surface and the microwells defined thereby. Each well, microwell, microchannel, and/or immobilization site may be configured to receive and grow at least one cell; however, in use, any given well, microwell, microchannel, or immobilization site may or may not actually receive and/or grow one or more cells. Types of experimental units may be interchangeable. For example, embodiments herein that expressly describe microwells are also intended to disclose embodiments in which the microwells are at least in part replaced with microchannels, immobilization sites, and/or other types of experimental units. 
     One or more portions of a microfabricated device may be selected, treated, and/or coated with a surface chemistry modifier to have a particular surface chemistry. For example, at least a portion of a substrate surface may be configured with first surface characteristics that repel cells and/or reduce cellular tendency to stick to the surface or second surface characteristics that attract cells and/or increase cellular tendency to attach to the surface. Depending on the type of target cell, the material and/or coating may be hydrophobic and/or hydrophilic. At least a portion of the top surface of the substrate may be treated to have first surface characteristics that repel target cells and/or reduce the tendency of target cells to stick to the surface. Meanwhile, at least a portion of the inner surface of each experimental unit, well, or microwell may be treated to have second surface characteristics that attract target cells and increase the tendency of target cells to occupy the experimental unit, well, or microwell. A surface of a substrate may have a plurality of portions with different surface characteristics. 
     A surface chemistry modifier may be applied using chemical vapor deposition, electroporation, plasma treatment, and/or electrochemical deposition. The surface chemistry modifier may control surface potential, Lund potential, zeta potential, surface morphology, hydrophobicity, and/or hydrophilicity. The surface chemistry modifier may include a silane, a polyelectrolyte, a metal, a polymer, an antibody, and/or a plasma. For example, the surface chemistry modifier may include octadecyltrichlorosilane. The surface chemistry modifier may include a dynamic copolymer, such as polyoxyethylene (20) sorbitan monolaurate and/or polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether. The surface chemistry modifier may include a static copolymer, such as poloxamer 407, poly(L-lysine), and/or a poly(ethylene glycol)-poly(1-lysine) block copolymer. 
     An apparatus for screening different conditions against a matrix of cells may include a substrate with a surface defining an array of microwells. Sections of the microwell array may be partitioned into subarrays (e.g., by larger wells or walls). The substrate may be microfabricated. Each microwell may receive and grow at least one biological entity (e.g., cell). The resulting matrix of biological entities (e.g., cells) may be a high density matrix of biological entities. The first array and/or the second array may be planar, substantially planar, and/or multi-planar (e.g., on a roll). 
     The term “high resolution” may refer to a capability of a system or method to distinguish between a number of available experiments. For example, a “high resolution” system or method may select an experimental unit from a microfabricated device comprising a high density of experimental units, in which the experimental unit has a diameter from about 1 nm to about 800 μm. A substrate of a microfabricated device or chip may include about or more than 10,000,000 microwells. For example, an array of microwells may include at least 96 locations, at least 1,000 locations, at least 5,000 locations, at least 10,000 locations, at least 50,000 locations, at least 100,000 locations, at least 500,000 locations, at least 1,000,000 locations, at least 5,000,000 locations, or at least 10,000,000 locations. 
     The surface density of microwells may be from about 150 microwells per cm 2  to about 160,000 microwells per cm 2  or more. A substrate of a microfabricated device or chip may have a surface density of microwells of at least 150 microwells per cm 2 , at least 250 microwells per cm 2 , at least 400 microwells per cm 2 , at least 500 microwells per cm 2 , at least 750 microwells per cm 2 , at least 1,000 microwells per cm 2 , at least 2,500 microwells per cm 2 , at least 5,000 microwells per cm 2 , at least 7,500 microwells per cm 2 , at least 10,000 microwells per cm 2 , at least 50,000 microwells per cm 2 , at least 100,000 microwells per cm 2 , or at least 160,000 microwells per cm 2 . 
     The dimensions of a microwell may range from nanoscopic (e.g., a diameter from about 1 to about 100 nanometers) to microscopic or larger. For example, each microwell may have a diameter of about 1 μm to about 800 μm, a diameter of about 25 μm to about 500 μm, or a diameter of about 30 μm to about 100 μm. A microwell may have a diameter of about or less than 1 μm, about or less than 5 μm, about or less than 10 μm, about or less than 25 μm, about or less than 50 μm, about or less than 100 μm, about or less than 200 μm, about or less than 300 μm, about or less than 400 μm, about or less than 500 μm, about or less than 600 μm, about or less than 700 μm, or about or less than 800 μm. 
     A microwell may have a depth of about 500 μm to about 5000 μm, a depth of about 1 μm to about 500 μm, or a depth of about 25 μm to about 100 μm. A microwell may have a depth of about 1 μm, about 5 μm, about 10 μm, about 25 μm, about 50 μm, about 100 μm, about 200 μm, about 300 μm, about 400 μm, about 500 μm, about 600 μm, about 700 μm, about 800 μm, about 1000 μm, about 1,500 μm, about 2,000 μm, about 3,000 μm, or about 5,000 μm. 
     Each microwell may have an opening that is round, hexagonal, or square. Each microwell may include sidewalls. The sidewalls may have a cross-sectional profile that is straight, oblique, and/or curved. At least one unique location-specific tag, as described further below, may be disposed in at least one microwell of the high density array of microwells to facilitate identification of a species and a correlation of a species to a specific microwell of the high density array of microwells. The at least one unique tag may be disposed and/or positioned at the bottom of the microwell and/or on at least one side of the microwell. The at least one unique tag may include a nucleic acid molecule with a target-specific nucleotide sequence for annealing to a target nucleic acid fragment of the at least one biological entity and a location-specific nucleotide sequence for identifying the at least one microwell of the high density array of microwells. 
     For example, a substrate of a microfabricated device or chip may have a surface with dimensions of about 4 inches by 4 inches. The surface may define an array of approximately 100 million microwells. The microwell array may be partitioned into about 100 subsections by walls and/or the substrate may define an array of about 100 wells, with about one million microwells defined within each subsection or well totaling to approximately 100 million microwells. For a use case of testing different nutrients, microorganisms from an environmental sample may be loaded on the chip such that individual microorganisms or clusters of microorganisms partition into the microwells on the chip, each microwell being located at the bottom of a larger well. Each larger well may include an experimental unit such that about 100 different nutrients may be tested in parallel or in series on the same chip, with each well providing up to 1 million test cases. 
     Target cells may be Archaea, Bacteria, or Eukaryota (e.g., fungi, plants, or animals). For example, target cells may be microorganisms, such as aerobic, anaerobic, and/or facultative aerobic microorganisms. Different nutrients may be tested in parallel or in series on a composition of target cells to analyze and compare, for instance, growth or other effects on cell population, cell components, and/or cell products. A composition of target cells may be screened for a cell component, product, and/or capability, such as one or more of a virus (e.g., a bacteriophage), a cell surface (e.g., a cell membrane or wall), a metabolite, a vitamin, a hormone, a neurotransmitter, an antibody, an amino acid, an enzyme, a protein, a saccharide, ATP, a lipid, a nucleoside, a nucleotide, a nucleic acid (e.g., DNA or RNA), a phenotype, a mutation, a metabolic pathway, a gene, and an adaptation. 
     A composition of cells may include an environmental sample extract and/or a dilutant. The environmental sample extract and/or the dilutant may include, but is not limited to, one or more of a biological tissue (e.g., connective, muscle, nervous, epithelial, plant epidermis, vascular, ground, etc.), a biological fluid or other biological product (e.g., amniotic fluid, bile, blood, cerebrospinal fluid, cerumen, exudate, fecal matter, gastric fluid, interstitial fluid, intracellular fluid, lymphatic fluid, milk, mucus, rumen content, saliva, sebum, semen, sweat, urine, vaginal secretion, vomit, etc.), a microbial suspension, air (including, e.g., different gas contents), supercritical carbon dioxide, soil (including, e.g., minerals, organic matter, gases, liquids, organisms, etc.), sediment (e.g., agricultural, marine, etc.), living organic matter (e.g., plants, insects, other small organisms and microorganisms), dead organic matter, forage (e.g., grasses, legumes, silage, crop residue, etc.), a mineral, oil or oil products (e.g., animal, vegetable, petrochemical), alcohol, a buffer, an organic solvent, water (e.g., naturally-sourced freshwater, drinking water, seawater, etc.), and/or sewage (e.g., sanitary, commercial, industrial, and/or agricultural wastewater and surface runoff). 
     A method may include, prior to applying (e.g., loading) a composition including cells to a microfabricated device, preparing the composition by combining the cells with an environmental sample extract and/or a dilutant. The method further may include liquefying the environmental sample extract and/or the dilutant. A concentration of cells in a composition may be adjusted to target distribution of one cell per experimental unit, well, or microwell. 
     If a sample contains cells and/or viruses, the cells in the sample may be lysed after they are applied to a microfabricated device to release nucleic acid molecules. Cells may be lysed with chemical treatment such as alkaline exposure, detergents, sonication, enzymatic proteinase K, or lysozyme exposure. Cells may also be lysed by heating. 
       FIG. 5A  is a flowchart illustrating a method for isolating cells from a sample in accordance with some embodiments. In step  500 , a sample is obtained. In step  502 , the sample is homogenized and/or dispersed using at least one of a physical technique (e.g., blending and/or sonication) and a chemical technique (e.g., chelating agents, detergents, and/or enzymes). In step  504 , cells in the homogenized and/or dispersed sample are separated by density centrifugation using, for example, Nycodenz® non-particulate medium (available from Progen Biotechnik GmbH, Heidelberg, Germany). 
       FIG. 5B  is a diagram illustrating a method for isolating cells from a soil sample in accordance with some embodiments. Panel  506  shows the soil sample. Panel  508  shows the homogenized and/or dispersed sample in a test tube. Panel  510  shows the sample after centrifugation, separated into soluble debris  512 , cells  514 , insoluble debris  516 , and Nycodenz®  518 . 
       FIG. 6  is a flowchart illustrating a method for isolating and cultivating cells from a sample in accordance with some embodiments. In step  600 , a sample is obtained. In step  602 , at least one cell is extracted from the obtained sample. In step  604 , at least one high density microwell array of a microfabricated device or chip is loaded with the at least one extracted cell. Step  604  may include preparing a cell concentration with the at least one extracted cell, selecting at least one nutrient/media, and/or selecting at least one membrane. In step  606 , at least a portion of the microwell array is sealed with the at least one selected membrane to retain the cell concentration with the microwells. In step  608 , the chip is incubated. Step  608  may include selecting a temperature, determining atmosphere (e.g., aerobic or anaerobic), and/or timing incubation). In step  610 , the chip is split and/or substantially replicated (using, e.g., a picker), resulting in two portions of cultivated cells according to methods described herein. For example, the at least one membrane may be peeled off such that a portion of the cultivated cells remain attached or peeled off or punctured to sample the cultivated cells. In optional step  612 , one portion of the cultivated cells is sacrificed for identification. Step  612  may include PCR, sequencing, and/or various data analytics. In step  614 , strains of interest are identified. Further cultivation, testing, and/or identification may be performed with, for example, the strains of interest and/or the remaining portion of the cultivated cells. 
       FIG. 7  is a diagram illustrating a method for isolating and cultivating cells from a complex sample in accordance with some embodiments. Panel  700  shows examples of complex samples, specifically a microbiome sample  702  and a soil sample  704 . In Panel  706 , at least one cell is extracted from the sample using, for example, the protocol illustrated in  FIGS. 5A and 5B . In Panel  708 , the at least one extracted cell (and any environmental extract and/or dilutant) is loaded on a microfabricated device or chip with at least one high density microwell array  710 . Chip  710  and a reagent cartridge  712  may be loaded into an incubator  714 . The reagent may be useful for adding liquid to maintain nutritional requirements for growth and/or various screening purposes. Panel  716  shows the output: isolated strains of cultivated cells. 
     To identify the species or taxonomic lineage of cells or microorganisms growing in a microwell requires techniques including, but not limited to, DNA sequencing, nucleic acid hybridization, mass spectrometry, infrared spectrometry, DNA amplification, and antibody binding to identify genetic elements or other species identifiers. Many identification methods and process steps kill the microorganisms and therefore prevent further cultivation and study of microorganisms of interest. To enable both the identification of cells or microorganisms while enabling subsequent cultivation, study, and further elaboration of particular clones of interest, further embodiments are designed for sampling each experimental unit, well, or microwell across a substrate or chip while maintaining the locational integrity and separation of microorganism populations across experimental units, wells, or microwells. 
     A substrate as described above may enable sampling a cell population using further systems, kits, apparatus, and methods. For example, a picking device may be applied to a first surface of the substrate. The device may include at least one protrusion facing the first surface. The at least one protrusion has a diameter less than the opening diameter of each microwell, well, or experimental unit. The at least one protrusion may be inserted into at least one microwell, well, or experimental unit holding a population of cells such that a portion of the population of cells in the at least one microwell, well, or experimental unit adheres and/or attaches to the at least one protrusion. The sample of the population of cells in the at least one microwell, well, or experimental unit may be withdrawn by removing the device from the first surface of the substrate such that the portion of the population of cells in the at least one microwell, well, or experimental unit remains adhered and/or attached to the at least one protrusion. Each protrusion may be a pin or a plurality or assembly of pins. 
       FIGS. 8A-8C  are diagrams illustrating picking by one pin or multiple pins in accordance with some embodiments. Chip  800  is provided for inspection via a microscope  802  and picking via picking control device  804 . In  FIG. 8A , picking control device  804  comprises an arm with a single pin  806 . In  FIG. 8B , an arm with multiple pins  808  is shown.  FIG. 8C  is a perspective view of the chip during the picking process. 
       FIGS. 9A-9D  are images demonstrating picking of a well in accordance with some embodiments. In  FIG. 9A , the well is full. In  FIG. 9B , the pin is moved into position. In  FIG. 9C , the well is picked. In  FIG. 9D , a sample is removed from the well. 
       FIGS. 10A-10D  are diagrams illustrating a tool for picking a chip in accordance with some embodiments. In  FIG. 10A , a tool comprising a plurality of pins is aligned with a chip having a plurality of wells. In  FIG. 10B , the tool is lowered such that the pins are dipped into the wells. In  FIG. 10C , the pins are shown with samples attached, and the samples are transferred to a new chip. Alternatively, in  FIG. 10D , the tool is flipped such that the samples may be maintained in the tool itself. 
       FIG. 11  is an image of a well that has been picked through a thin layer of agar, illustrating picking through a membrane or sealing layer in accordance with some embodiments. 
     Alternatively, when the at least one protrusion is inserted into the at least one microwell, well, or experimental unit, a portion of the population of cells in the at least one the at least one microwell, well, or experimental unit is volume displaced up and around the at least one protrusion such that at least some of the volume displaced portion is above the first surface of the substrate and/or the inner surface of the at least one microwell, well, or experimental unit. The method also includes sampling the population of cells in the at least one microwell by collecting at least some of the volume displaced portion of the population of cells. 
     A similar picking device may be applied to a second surface opposite the first surface of the substrate. The device may include at least one protrusion facing the second surface. The at least one protrusion has a diameter about equal to or less than a diameter of at least one microwell, well, or experimental unit. The at least one protrusion is pushed against the second surface at a location corresponding to the at least one microwell, well, or experimental unit holding a population of cells and/or inserted into the at least one microwell, well, or experimental unit holding the population of cells such that a portion of the population of cells in the at least one microwell, well, or experimental unit is displaced above the first surface of the substrate and/or the inner surface of the at least one microwell, well, or experimental unit. The displaced portion of the population of cells may then be collected. The population of cells may be located on a plug (e.g., a hydrogel or other soft material like agar) in the at least one experimental unit, well, or microwell such that when the at least one protrusion is at least one of pushed against the second surface and inserted into the at least one microwell, the plug is displaced, thereby displacing the portion of the population of cells. 
     The sample of the population of cells from the at least one experimental unit, well, or microwell may be deposited in a second location. The at least one protrusion may be cleaned and/or sterilized prior to further sampling. At least a portion of the at least one protrusion may be composed of a material, treated, and/or coated with a surface chemistry modifier for surface characteristics that favor attachment of cells. The at least one protrusion may be an array of protrusions. Upon applying the device to the first surface of the substrate, the array of protrusions may be inserted into a corresponding array of experimental units, wells, or microwells. The number of protrusions in the array of protrusions may correspond to the number of experimental units in the first array, the number of microwells in one second array of microwells, or the total number of microwells in the substrate. 
     Another device for sampling a cell population in a substrate includes at least one needle and/or nanopipette facing the first surface. The at least one needle and/or nanopipette has an external diameter less than the opening diameter of each microwell and an internal diameter capable of accommodating a target cell diameter. The at least one needle and/or nanopipette is inserted into at least one experimental unit, well, or microwell holding a population of cells. The sample of the population of cells in the at least one experimental unit, well, or microwell is withdrawn using pressure to pull a portion of the population of cells from the at least one experimental unit, well, or microwell into the device. 
     The sample of the population of cells from the at least one experimental unit, well, or microwell may be deposited in a second location. The at least one needle and/or nanopipette may be cleaned and/or sterilized prior to further sampling. The at least one needle and/or nanopipette may be an array of needles and/or nanopipettes. Upon applying the device to the first surface of the microfabricated substrate, the array of needles and/or nanopipettes may be inserted into a corresponding array of experimental units, wells, or microwells. The number of needles and/or nanopipettes in the array of needles and/or nanopipettes may correspond to the number of the experimental units in the first array, the number of microwells in one second array of microwells, or the total number of microwells in the substrate. 
     Another method for sampling a cell population in a substrate includes applying focused acoustic energy to at least one experimental unit, well, or microwell holding a population of cells in fluid. The focused acoustic energy may be applied in a manner effective to eject a droplet from the at least one microwell, such as, for example, acoustic droplet ejection (ADE) (see, e.g., Sackmann et al., “Acoustical Micro- and Nanofluidics: Synthesis, Assembly and Other Applications,”  Proceedings of the  4 th European Conference on Microfluidics  (December 2014)). The droplet may include a sample of the population of cells in the at least one experimental unit, well, or microwell. The droplet may be directed into a second container or surface or substrate. 
     A substrate may include at least a first piece including at least a portion of the first surface and a second piece including at least a portion of the second surface. The first piece and the second piece are detachably connected along at least a portion of a plane parallel to the first surface and the second surface. The plane divides the experimental units, wells, or microwells. A cell population in at least one experimental unit, well, or microwell is sampled by detaching the first piece and the second piece such that a first portion of the population of cells in the at least one experimental unit, well, or microwell remains attached to the first piece and a second portion of the population of cells in the at least one experimental unit, well, or microwell remains attached to the second piece. 
       FIG. 12  is a diagram illustrating a cross-section of a chip  1200  in accordance with some embodiments. Chip  1200  includes a substrate defining an array of wells  1202  filled with contents  1204 . The substrate comprises a first piece  1206  and a second piece  1208 . The first piece  1206  and the second piece  1208  are detachably connected along a plane  1210  parallel to and bisecting the array of wells  1202 . When the first piece  1206  and the second piece  1208  are detached, the wells  1202  and their contents  1204  are divided, resulting in two copies of the contents  1204  that preserve both the isolation and the location of the contents  1204  on chip  1200 . 
     Each microwell, experimental unit, or microchannel may include a partial barrier that partially separates the microwell, experimental unit, or microchannel into a first portion and a bottom portion such that a cell population is able to grow in both the first portion and the bottom portion. Prior to sampling the population of cells, the above methods may include dispersing and/or reducing clumps of cells in the population of cells. Dispersing and/or reducing clumps of cells in the population of cells may include, but is not limited to, applying sonication, shaking, and dispension with small particles. 
     The above methods further may include depositing the sample of the population of cells from the at least one experimental unit, well, or microwell in a second location. The second location may be a corresponding array of experimental units, wells, or microwells. The second location may be a single receptacle. The sample of the population of cells from the at least one experimental unit, well, or microwell may be maintained for subsequent cultivation. Alternatively, the remaining cells of the population of cells in the at least one experimental unit, well, or microwell may be maintained for subsequent cultivation. 
     The above methods further may include identifying at least one cell from the sample of the population of cells and/or the remaining cells of the population of cells. This may include performing DNA, cDNA, and/or RNA amplification, DNA and/or RNA sequencing, nucleic acid hybridization, mass spectrometry, and/or antibody binding. Alternatively, or in addition, this may include identifying an experimental unit, well, or microwell from which at least one cell originated. Each experimental unit, well, or microwell may be marked with a unique tag including a location-specific nucleotide sequence. To identify the experimental unit, well, or microwell, a location-specific nucleotide sequence may be identified in the sequencing and/or amplification reaction, and the location specific nucleotide sequence may be correlated with the at least one experimental unit, well, or microwell from which the at least one cell originated. 
     A microfabricated device as described above may enable culturing cells in a sample derived from an environment using further systems, kits, apparatus, and methods. For example, a sample may be applied to the first surface of a substrate such that at least one of the cells occupies at least one microwell, well, or experimental unit. A semi-permeable membrane is applied to at least a portion of the first surface (e.g., at least a portion of an inner surface of an experimental unit or well) such that a nutrient can diffuse into the at least one microwell, well, or experimental unit. Meanwhile, escape of the occupying cells from the at least one microwell, well, or experimental unit is prevented and/or mitigated. A semi-permeable membrane may be, for example, a hydrogel layer. A semi-permeable membrane may be reversibly or irreversibly connected or affixed to the substrate using, for example, lamination. Thus, the occupying cells may be incubated in the at least one microwell, well, or experimental unit with at least one nutrient. The cells may be gradually transitioned over a period of time from at least one nutrient to at least one alternative nutrient or nutrient formulation using progressive partial exchange, thereby undergoing domestication or adaptation. 
     A first nutrient derived from the environment may be used to incubate the cells occupying at least one first experimental unit, well, or microwell, and a second nutrient derived from the environment may be used to incubate the cells occupying at least one second experimental unit, well, or microwell. The above methods may include comparing the cells occupying the at least one first experimental unit, well, or microwell with the cells occupying at least one second experimental unit, well, or microwell to analyze the first nutrient and the second nutrient. 
     For example, a method may include one or more of the following steps:
         Acquire a chip defining 1000 to 10 million or more microwells within a number of larger wells or flow cells, each microwell having a diameter of about 1 μm to about 800 μm and a depth of about 1 μm to about 800 μm, the chip further having one or more surface chemistries configured to facilitate the movement of target microorganisms into the microwells;   Apply an environmental sample or a derivative of the environmental sample to the chip such that any target microorganisms become located in the microwells;   Place one or more semi-permeable filters, hydrogel layers, or other barriers on the chip such that a barrier is created that allows nutrients to diffuse into the microwells but prevents and/or mitigates escape of microorganisms from the microwells;   Incubate the chip with at least one nutrient (e.g., derived from the environment);   Gradually change the nutrient source by progressive partial exchange with at least one alternative nutrient (e.g., formulation); and   Detect any growth of microorganisms in the microwells.       

     The target cells may be Archaea, Bacteria, or Eukaryota. Target viruses may be bacteriophages. When viruses are targeted, the microwells of the chip may also include host cells in which the viruses may grow. Detecting the growth of the occupying cells or viruses may include detecting a change in biomass (e.g., DNA/RNA/protein/lipid), metabolite presence or absence, pH, consumption of nutrients, and/or consumption of gases. Detecting the growth of the occupying cells or viruses may include performing real-time sequential imaging, microscopy, optical density, fluorescence microscopy, mass spectrometry, electrochemistry, amplification (DNA, cDNA, and/or RNA), sequencing (DNA and/or RNA), nucleic acid hybridization, and/or antibody binding. 
       FIG. 13  is a flowchart illustrating methods for screening in accordance with some embodiments. In step  1300 , a sample is obtained. In step  1302 , at least one cell is extracted from the obtained sample. In step  1304 , at least one high density microwell array of a microfabricated device or chip is loaded with the at least one extracted cell. Step  1304  may include preparing a cell concentration with the at least one extracted cell, selecting at least one nutrient/media, and/or selecting at least one membrane. In step  1306 , at least a portion of the microwell array is sealed with the at least one selected membrane to retain the cell concentration with the microwells. In step  1308 , the chip is incubated. Step  1308  may include selecting a temperature, determining atmosphere (e.g., aerobic or anaerobic), and/or timing incubation). A genetic screen and/or a functional screen may be performed. In step  1310 , a genetic screen is applied to the chip. In step  1312 , the chip is split and/or substantially replicated (using, e.g., a picker), resulting in two portions of cultivated cells according to methods described herein. For example, the at least one membrane may be peeled off such that a portion of the cultivated cells remain attached or peeled off or punctured to sample the cultivated cells. In optional step  1314 , one portion of the cultivated cells is sacrificed for identification. Step  1314  may include PCR, sequencing, and/or various data analytics. In step  1316 , strains of interest are identified. Further cultivation, testing, and/or identification may be performed with, for example, the strains of interest and/or the remaining portion of the cultivated cells. Alternatively, in step  1318 , a functional screen is applied to the chip. In step  1320 , one or more variables are observed and, as in step  1316 , strains of interest are identified. 
       FIG. 14  is a diagram illustrating a screening method in accordance with some embodiments. Panel  1400  shows examples of complex samples, specifically a microbiome sample  1402  and a soil sample  1404 . In Panel  1406 , at least one cell is extracted from the sample using, for example, the protocol illustrated in  FIGS. 5A and 5B . In Panel  1408 , the at least one extracted cell (and any environmental extract and/or dilutant) is loaded on a microfabricated device or chip with at least one high density microwell array  1410 . Chip  1410  and a reagent cartridge  1412  may be loaded into an incubator  1414 . The reagent may be useful for adding liquid to maintain nutritional requirements for growth and/or various screening purposes. Panel  1416  shows the output: screen results and isolated strains of cultivated cells. 
       FIG. 15  is a series of images illustrating a screening example in accordance with some embodiments. The images show portions of a chip with a membrane and an acid-sensitive layer applied thereon to screen for low pH. In image  1500 , more than 1800, 50-μm microwells are visible with nine clear hits  1502 . Image  1504  is a magnified view of box  1504 , and image  1506  is a magnified view of one of the microwells with a hit  1502 . 
       FIGS. 16A-16C  are images illustrating recovery from a screen in accordance with some embodiments. In  FIG. 16A , at least one well is picked using a microscope and a picking device with at least one pin. In  FIG. 16B , a pin is removed and incubated in media. In  FIG. 16C , growth is visible. 
       FIG. 17A  is an exploded diagram illustrating a chip for screening in accordance with some embodiments. In  FIG. 17A , chip  1700  includes a high density array of microwells with, for example, soil microbes in the microwells. Membrane  1702  is applied to chip  1700 . Gasket  1704  is applied to chip  1700  over membrane  1702 . Agar with fluorescent  E. coli  bacteria  1706  is applied to chip  1700  over gasket  1704  and membrane  1702 .  FIGS. 17B and 17C  are images illustrating a screening example in accordance with some embodiments. In this example, the screen is for clearance zones.  FIG. 17B  is a fluorescence image of a chip, prepared like chip  1700  in  FIG. 17A , following the screen.  FIG. 17C  is an image showing a process of picking a sample from this chip through the agar. 
     In some embodiments, a location on an apparatus may be correlated with a portion of a sample present at that location, after that portion of the sample (or a part of the portion) is removed from the apparatus. The apparatus may be or include a microarray. The microarray may comprise a plurality of locations for applying a sample, wherein each location is marked with a unique tag which may be used to identify the location from which a portion of the sample came, after that portion of the sample is removed from the microarray. 
     The disclosure relates to a method of identifying from which location on a microarray a portion of a sample comprising at least one nucleic acid molecule came, after that portion of the sample is removed from the microarray, the method comprising the steps of: (a) applying one or more portions of the sample onto one or more of a plurality of locations on the microarray, wherein each location is marked with a unique tag comprising a nucleic acid molecule comprising: (i) a location-specific nucleotide sequence; and (ii) a first target-specific nucleotide sequence; (b) allowing the target nucleic acid molecule found in at least one portion of the sample to anneal to a tag marking a location; (c) performing primer extension, reverse transcription, single-stranded ligation, or double-stranded ligation on the population of annealed nucleic acid molecules, thereby incorporating a location-specific nucleotide sequence into each nucleic acid molecule produced by primer extension, reverse transcription, single-stranded ligation, or double-stranded ligation; (d) combining the population of nucleic acid molecules produced in step (c); (e) sequencing the population of combined nucleic acid molecules, thereby obtaining the sequence of one or more location-specific nucleotide sequences; and (f) correlating the sequence of at least one location-specific nucleotide sequence obtained from the population of combined nucleic acid molecules to the location on the microarray marked with a tag comprising said location-specific nucleotide sequence; thereby identifying from which location on a microarray a portion of a sample comprising at least one nucleic acid molecule came. In some embodiments, a sample may include at least one cell and one or more nucleic acid molecules are released from the cell after step (a) and before step (b). A sample may include at least one cell, and the at least one cell replicates or divides after step (a) and before step (b). A portion of the portion of the sample may be removed from at least one location before step (b) and said portion of the portion of the sample may be stored in a separate receptacle correlated to the original location of the portion of the sample on the microarray. The method of correlating or identifying a location may further comprise the step of amplifying the nucleic acid molecules produced in step (c) or the population of combined nucleic acid molecules produced in step (d). The amplifying step may comprise polymerase chain reaction amplification, multiplexed polymerase chain reaction amplification, nested polymerase chain reaction amplification, ligase chain reaction amplification, ligase detection reaction amplification, strand displacement amplification, transcription based amplification, nucleic acid sequence-based amplification, rolling circle amplification, or hyper-branched rolling circle amplification. Additional primers may be added during an amplification reaction. For example, both 5′ and 3′ primers may be needed for a PCR reaction. One of the primers used during an amplification reaction may be complementary to a nucleotide sequence in the sample. 
     In some embodiments, a composition including cells and/or viruses may be treated with a nuclease before the composition is applied to a microfabricated device so that contaminating nucleic acid molecules are not amplified in subsequent steps. 
     The sequencing used in the disclosed methods and apparatuses may be any process of obtaining sequence information, including hybridization and use of sequence specific proteins (for example, enzymes). Sequencing may comprise Sanger sequencing, sequencing by hybridization, sequencing by ligation, quantitative incremental fluorescent nucleotide addition sequencing (QIFNAS), stepwise ligation and cleavage, fluorescence resonance energy transfer, molecular beacons, TaqMan reporter probe digestion, pyrosequencing, fluorescent in situ sequencing (FISSEQ), wobble sequencing, multiplex sequencing, polymerized colony (POLONY) sequencing (see, e.g., U.S. Patent Application Publication No. 2012/0270740, which is incorporated by reference herein in its entirety); nanogrid rolling circle (ROLONY) sequencing (see, e.g., U.S. Patent Application Publication No. 2009/0018024, which is incorporated by reference herein in its entirety), allele-specific oligo ligation assay sequencing, or sequencing on a next-generation sequencing (NGS) platform. Non-limiting examples of NGS platforms include systems from Illumina® (San Diego, Calif.) (e.g., MiSeq™, NextSeq™, HiSeq™, and HiSeq X™), Life Technologies (Carlsbad, Calif.) (e.g., Ion Torrent™), and Pacific Biosciences (Menlo Park, Calif.) (e.g., PacBio® RS II). 
     An organism or species may be identified by comparing the nucleic acid sequence obtained from that organism to various databases containing sequences of organisms. For example, ribosomal RNA sequence data is available in the SILVA rRNA database project (Max Planck Institute for Marine Microbiology, Bremen, Germany (www.arb-silva.de); see, e.g., Quast et al., “The SILVA Ribosomal RNA Gene Database Project: Improved Data Processing and Web-Based Tools,” 41  Nucl. Acids Res . D590-D596 (2013), and Pruesse et al., “SINA: Accurate High-Throughput Multiple Sequence Alignment of Ribosomal RNA Genes,” 28  Bioinformatics  1823-1829 (2012), both of which are incorporated by reference herein in their entirety). Other ribosomal RNA sequence databases include the Ribosomal Database Project (Michigan State University, East Lansing, Mich. (www.rdp.cme.msu.edu); see, e.g., Cole et al., “Ribosomal Database Project: Data and Tools for High Throughput rRNA Analysis” 42  Nucl. Acids Res . D633-D642 (2014), which is incorporated by reference herein in its entirety) and Greengenes (Lawrence Berkeley National Laboratory, Berkeley, Calif. (www.greengenes.lbl.gov); see, e.g., DeSantis et al., “Greengenes, a Chimera-Checked 16S rRNA Gene Database and Workbench Compatible with ARB,” 72  Appl. Environ. Microbiol.  5069-72 (2006), which is incorporated by reference herein in its entirety). The GenBank® genetic sequence database contains publicly available nucleotide sequences for almost 260,000 formally described species (National Institutes of Health, Bethesda, Md. (www.ncbi.nlm.nih.gov); see, e.g., Benson et al., “GenBank,” 41  Nucl. Acids Res . D36-42 (2013). 
     The sequence used for matching and identification may include the 16S ribosomal region, 18S ribosomal region or any other region that provides identification information. The desired variant may be a genotype (e.g., single nucleotide polymorphism (SNP) or other type of variant) or a species containing a specific gene sequence (e.g., a sequence coding for an enzyme or protein). An organism or species may also be identified by matching its sequence to a custom internal sequence database. In some cases, one may conclude that a certain species or organism is found at a location on the microarray if the sequence obtained from the portion of the sample at the location has at least a specified percentage identity (e.g., at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity) to the known DNA, cDNA, or RNA sequence obtained from that species or microorganism. 
     The disclosure further relates to a method of manufacturing a microarray comprising a plurality of locations for applying a sample, wherein at least one location is marked with a unique tag, the method comprising the steps of: (a) synthesizing a plurality of tags, wherein each tag comprises a nucleic acid molecule comprising: (i) a location-specific nucleotide sequence; and (ii) a target-specific nucleotide sequence; and (b) placing a tag on at least one location of the plurality of locations on the microarray. In an alternative embodiment, the disclosure relates to a method of manufacturing a microarray comprising a plurality of locations for applying a sample, wherein at least one location is marked with a unique tag, the method comprising the steps of: (a) synthesizing a plurality of tags, wherein each tag comprises a nucleic acid molecule comprising: a target-specific nucleotide sequence and not comprising a location-specific nucleotide sequence; and (b) placing a tag on at least one location of the plurality of locations on the microarray. The target-specific sequence may be the same at every location in the microarray. In either of the above embodiments, step (a) may be performed before step (b). The placing step (b) may comprise placing the tag at each location by a liquid handling procedure (for example, pipetting, spotting with a solid pin, spotting with a hollow pin, or depositing with an inkjet device). At least one tag may include a nucleic acid molecule or a portion of a nucleic acid molecule that is pre-synthesized. Step (a) may be performed simultaneously with step (b). In certain embodiments, at least one tag comprises a nucleic acid molecule that is synthesized at each location by in situ synthesis. The synthesizing step (a) may comprise inkjet printing synthesis or photolithography synthesis. 
     Each location on a microarray may be configured to receive a portion of the sample. A location may be tagged or labeled with a nucleic acid molecule (e.g., an oligonucleotide) that comprises at least one of: (i) a location-specific nucleotide sequence (e.g., a barcode); and (ii) a target-specific nucleotide sequence. A target-specific nucleotide sequence may complement or substantially complement a nucleotide sequence found in the sample. The order of the nucleotide sequences from the 5′ end to the 3′ end in the nucleic acid molecule may be: (1) a location-specific nucleotide sequence; and (2) a target-specific nucleotide sequence. Alternatively, the order of the nucleotide sequences from the 5′ end to the 3′ end in the nucleic acid molecule may be (2) then (1). The nucleic acid molecule may be attached at its 5′ end to the microarray. One or more locations on the apparatus (e.g., microarray) may be untagged or unlabeled. 
     The terms “complementary” or “substantially complementary” may refer to the hybridization, the base pairing, or the formation of a duplex between nucleotides or nucleic acids, such as, for instance, between the two strands of a double stranded DNA molecule or between an oligonucleotide primer and a primer binding site on a single stranded nucleic acid. Complementary nucleotides are, generally, A and T/U, or C and G. Two single-stranded RNA or DNA molecules are said to be substantially complementary when the nucleotides of one strand, optimally aligned and compared and with appropriate nucleotide insertions or deletions, pair with at least about 80% of the nucleotides of the other strand, usually at least about 90% to 95%, and more preferably from about 98 to 100%. Alternatively, substantial complementarity exists when an RNA or DNA strand will hybridize under selective hybridization conditions to its complement. Typically, selective hybridization will occur when there is at least about 65% complementary over a stretch of at least 14 to 25 nucleotides, at least about 75%, or at least about 90% complementary. 
     The term “selectively hybridize” or “selective hybridization” may refer to binding detectably and specifically. Polynucleotides, oligonucleotides and fragments thereof selectively hybridize to nucleic acid strands under hybridization and wash conditions that minimize appreciable amounts of detectable binding to nonspecific nucleic acids. “High stringency” or “highly stringent” conditions can be used to achieve selective hybridization conditions as known in the art and discussed herein. An example of “high stringency” or “highly stringent” conditions is a method of incubating a polynucleotide with another polynucleotide, wherein one polynucleotide may be affixed to a solid surface such as a membrane, in a hybridization buffer of 6×SSPE or SSC, 50% formamide, 5×Denhardt&#39;s reagent, 0.5% SDS, 100 μg/ml denatured, fragmented salmon sperm DNA at a hybridization temperature of 42° C. for 12-16 hours, followed by twice washing at 55° C. using a wash buffer of 1×SSC, 0.5% SDS. 
     The nucleic acid molecule that is part of a location tag may comprise at least one deoxyribonucleotide or at least one ribonucleotide. The nucleic acid molecule may be single-stranded or double-stranded. A nucleic acid molecule may be a double-stranded molecule having a single-stranded overhang. 
     In some embodiments, the location tag may be used to amplify a nucleic acid molecule that anneals to it. Thus, the location tag may comprise a nucleic acid sequence that further comprises an amplification primer binding site. An amplification primer binding site may be at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25, at least 26, at least 27, at least 28, at least 29, or at least 30 nucleotides in length. The order of the nucleotide sequences from the 5′ end to the 3′ end in the nucleic acid molecule may be, for example: (1) the amplification primer binding site; (2) the location-specific nucleotide sequence; and (3) the target-specific nucleotide sequence. 
     In some embodiments, a nucleic acid molecule may comprise a target-specific nucleotide sequence without comprising a location-specific nucleotide sequence. In certain embodiments, a nucleic acid molecule may comprise a target-specific nucleotide sequence without comprising either a location-specific nucleotide sequence or an amplification binding site sequence. In further embodiments, a nucleic acid molecule may comprise only a target-specific nucleotide sequence. In even further embodiments, a nucleic acid molecule may contain only a target-specific nucleotide sequence. The amplification primer binding site may be capable of binding to a polymerase chain reaction primer, a multiplexed polymerase chain reaction primer, a nested polymerase chain reaction primer, a ligase chain reaction primer, a ligase detection reaction primer, a strand displacement primer, a transcription based primer, a nucleic acid sequence-based primer, a rolling circle primer, or a hyper-branched rolling circle primer. Additional primers may be added to the microarray during an amplification reaction. For example, both 5′ and 3′ primers may be needed for a PCR reaction. Target-specific nucleotide sequences may be amplified in the locations containing target nucleic acid molecules and may be detected by, for example, qPCR, end point PCR, and/or dyes to detect amplified nucleic acid molecules. 
     It may be desirable to sequence a nucleic acid molecule that anneals to a location tag or the amplified product based on such a nucleic acid molecule. The location tag may comprise a nucleic acid sequence that further comprises an adapter nucleotide sequence. In certain embodiments, an adapter nucleotide sequence may not be found in the location tag but is added to the sample nucleic acid molecules in a secondary PCR reaction or by ligation. An adapter nucleotide sequence may be a generic adapter or an adapter for a specific sequencing platform (e.g., Illumina® or Ion Torrent™). An adapter nucleotide sequence may include a sequencing primer binding site. A sequencing primer binding site may be capable of binding a primer for Sanger sequencing, sequencing by hybridization, sequencing by ligation, quantitative incremental fluorescent nucleotide addition sequencing (QIFNAS), stepwise ligation and cleavage, fluorescence resonance energy transfer, molecular beacons, TaqMan reporter probe digestion, pyrosequencing, fluorescent in situ sequencing (FISSEQ), wobble sequencing, multiplex sequencing, polymerized colony (POLONY) sequencing (see, e.g., US 2012/0270740); nanogrid rolling circle (ROLONY) sequencing (see, e.g., US 2009/0018024), allele-specific oligo ligation assay sequencing, sequencing on an NGS platform, or any suitable sequencing procedure. Non-limiting examples of NGS platforms include systems from Illumina® (San Diego, Calif.) (e.g., MiSeq™, NextSeq™, HiSeq™, and HiSeq X™), Life Technologies (Carlsbad, Calif.) (e.g., Ion Torrent™), and Pacific Biosciences (Menlo Park, Calif.) (e.g., PacBio® RS II). 
     A location-specific nucleotide sequence (e.g., a barcode) may be at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25, at least 26, at least 27, at least 28, at least 29, or at least 30 nucleotides in length. 
     A target-specific nucleotide sequence may be at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25 nucleotides, at least 26, at least 27, at least 28, at least 29, at least 30, at least 40, at least 50, at least 75, or at least 100 nucleotides in length. 
     At least one location on a microarray may be further marked with a unique molecular identifier tag. Unique molecular identifiers may be used to quantify growth (e.g., growth of a microorganism colony or replication of cells at the location). Unique molecular identifiers may be random nucleotide sequences. Methods using unique molecular identifiers and examples of unique molecular identifiers have been described in the art, see, e.g., WO 2013/173394, which is incorporated by reference herein in its entirety. For example, a unique molecular identifier tag may have the nucleotide sequence NNNANNNCNNNTNNNGNNNANNNCNNN (SEQ ID NO:1), wherein the Ns (equal random mix of ACGT) create a large encoding space so that each molecule amplified gets a unique (specific) DNA sequence barcode (4{circumflex over ( )}N barcodes, or 4{circumflex over ( )}21˜4 trillion in this example) This sequence can be counted without interference from amplification bias or other technical problems. The fixed bases in SEQ ID NO:1 (the A, C, G, T) help with reading the barcode accurately, e.g., handling indels. 
     The present disclosure encompasses using location-specific tags to monitor the presence or amount of more than one target-specific nucleotide sequence in a sample (e.g., multiplexing). At least one location on a microarray may be further marked with a second unique tag comprising a nucleic acid molecule comprising, for example: (i) an amplification primer binding site; (ii) a location-specific nucleotide sequence; and (iii) a target-specific nucleotide sequence. 
     In some embodiments, a nucleic acid molecule may comprise a target-specific nucleotide sequence without comprising a location-specific nucleotide sequence. In certain embodiments, a nucleic acid molecule may comprise a target-specific nucleotide sequence without comprising either a location-specific nucleotide sequence or an amplification binding site sequence. In further embodiments, a nucleic acid molecule may comprise only a target-specific nucleotide sequence. In even further embodiments, a nucleic acid molecule may contain only a target-specific nucleotide sequence. The target-specific nucleotide sequence may be at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25 nucleotides, at least 26, at least 27, at least 28, at least 29, at least 30, at least 40, at least 50, at least 75, or at least 100 nucleotides in length. In certain embodiments, the target-specific sequence may be the same at every location in the microarray. Additional target-specific nucleotide sequences may be monitored. For example, one or more locations may be marked with at least 10, at least 25, at least 50, at least 75, or at least 100 unique tags, wherein each tag comprises a target-specific nucleotide sequence that is different from the other target-specific nucleotide sequences in the tags at that location. 
     Any genetic locus of interest may provide a target-specific nucleotide sequence. For example, sequences of bacterial 16S ribosomal RNA (rRNA), 18S ribosomal RNA, poly(A) RNA, an RNA polymerase gene, a DNA polymerase gene, the RecA gene, a transposase gene, ribosomal internal transcribed spacer (ITS) sequences, a gene encoding an enzyme, control region DNA sequences, binding site DNA sequences, or a portion of any of these sequences may serve as a target-specific nucleotide sequence. A disclosed system, kit, apparatus, or method may use one or more of the bacterial 16S rRNA primers described in Sundquist et al., “Bacterial Flora-Typing with Targeted, Chip-Based Pyrosequencing,” 7:108  BMC Microbiology  (2007) and Wang et al., “Conservative Fragments in Bacterial 16S rRNA Genes and Primer Design for 16S Ribosomal DNA Amplicons in Metagenomic Studies,” 4:10  PLoS ONE  e7401 (2009), each of which is incorporated herein by reference in its entirety. 
     A sample used in the disclosed apparatuses and methods may comprise a plurality of nucleic acid molecules. A sample may comprise at least one DNA molecule or at least one RNA molecule. A sample may comprise at least one nucleic acid molecule formed by restriction enzyme digestion. A sample may comprise at least one cell (e.g., an archaebacterial cell, a eubacterial cell, a fungal cell, a plant cell, and/or an animal cell). A sample may comprise at least one microorganism. A sample may comprise one or more viruses (e.g., a bacteriophage), for which host cells may need to be provided. A portion of a sample at a location on a microarray may be a single cell or a colony grown from a single cell. For example, individual microorganisms or cells may be placed in microwells and the individual microorganisms or cells may be allowed to divide or replicate so that a colony grows within each microwell that had an individual microorganism or cell placed in it. A location on a microarray may thus contain a single microorganism species or a mixed community of microorganism strains that support one another&#39;s growth. A sample may comprise any suitable dilutant. In non-limiting examples, a sample comprises soil, sewage, fecal matter, contents of a body cavity, a biological fluid, living organic matter, dead organic matter, a microbial suspension, naturally-sourced freshwater, drinking water, seawater, wastewater, supercritical carbon dioxide, a mineral, a gas, a buffer, alcohol, an organic solvent, and/or an oil. In some embodiments, a nucleic acid molecule comprising (a) (i) a location-specific nucleotide sequence and (ii) one or more target-specific nucleotide sequences; or (b) one or more target-specific nucleotide sequences (i.e., not comprising a location-specific nucleotide sequence) is placed on at least one location on a microarray before a portion of a sample is placed at the location. In other embodiments, a nucleic acid molecule comprising (a) (i) a location-specific nucleotide sequence and (ii) one or more target-specific nucleotide sequences; or (b) one or more target-specific nucleotide sequences (i.e., not comprising a location-specific nucleotide sequence) is placed on at least one location on a microarray after a portion of a sample is placed at the location. In one example, a sample or a portion of a sample may be placed on a microarray and incubated before a nucleic acid molecule comprising at least one of: (i) a location-specific nucleotide sequence and (ii) a target-specific nucleotide sequence is placed on the microarray. In some embodiments, a portion of the portion of a sample may be removed from at least one location on the microarray and stored in a separate receptacle or the microarray may be split either before or after the nucleic acid molecules are placed on at least one location on the microarray. 
     At least one location-specific tag may comprise a nucleic acid molecule or a portion of a nucleic acid molecule that is pre-synthesized and placed at the location by a liquid handling procedure. For instance, a liquid handling procedure may be pipetting, spotting with a solid pin, spotting with a hollow pin, or depositing with an inkjet device. A tag may be generated at the location using multiple nucleic acid molecules that are pre-synthesized separately. At least one tag may comprise a nucleic acid molecule that is synthesized at the location by in situ synthesis (e.g., by inkjet printing or by photolithography). 
     Digital Enumeration of Species 
     A high density chip device comprised of a surface having high density microwells is described herein. Microbes from a microbiome sample may be diluted and applied to the device such that wells contain approximately one microbe per occupied well. The chip then may be incubated such that the microbes replicate within the wells. Further, a DNA based locational indexing system is described herein to determine what species is present in each well. This indexing system may involve having PCR primers preloaded into each well that contain addressing barcodes that identify the well and a primer sequence targeted to a specific genetic element (e.g., 16S) in the microbial genome that provides species information or targets a desired genetic sequence. After incubation, the microbial DNA is released, the PCR primers amplify the target bacterial DNA region, and the amplicons from the various wells on a chip are pooled and then may be read next generation sequencing. 
     The systems, kits, apparatus, and methodologies described herein may be utilized to perform an absolute count of the number of each microbial species or variant in a sample. Each well may represent a digital event which represents the presence of a single microbe in the original diluted sample. The locational indexing system may allow a user to determine what bacterial species is in the well. A unit of measurement may be “there is a bacterial species in a well” and may be independent of the number of bacteria in the well. 
     In one example, a mixed sample of microbes includes 50% Species 1, 30% Species 2, and 20% Species 3. The sample is diluted then applied to the chip such that each occupied well has, for the most part, one microbe. The microbe replicates. Note the replication rate may be different for different species. Then, the chip is processed such that the DNA from the microbes in the wells is released and the 16S or some other target sequence is amplified. The DNA amplification products from each well may be pooled and sequenced using next generation sequencing. The next generation sequencing data may be analyzed to determine, for each well, what species is in each occupied well. Many wells may not be occupied at all. The abundance of each species may be determined by: the total number of wells occupied by each species divided by the total number of occupied wells. An absolute abundance determination may be made by multiplying the % abundance of each species from step by the total number of microbes in the original sample. The sequencing data may be compared to publicly available sequence datasets to determine what species is in each occupied well. For example, ribosomal RNA sequence data is available in the SILVA rRNA database project described above. Other ribosomal RNA sequence databases include the Ribosomal Database Project, Greengenes, and the GenBank® genetic sequence database, also described above. 
     Current methods for estimating the abundance of microbial species in a sample involve the use of traditional techniques such as microscopy, staining, selective media, metabolic/physiological screens, and cultivation using petri dishes. These methods are often inaccurate due to lack of specificity (microscopy, staining, metabolic/physiological screens) or lack of ability to account for all species in a sample (selective media, cultivation) whereby many species do not grow well or do not grow at all with traditional approaches. 
     Current molecular methods for determining the relative abundance of microbial species in microbiome samples involve extracting microbial DNA from samples, performing PCR amplification of the 16S or some other DNA region that provide species or other information, then performing next generation sequencing (NGS) on the resulting PCR product. The relative abundance of each species in the original sample is inferred from the relative frequency of the species specific DNA sequence in the NGS data. There are many examples in the literature of this type of analysis and this method underpins much microbiome research. 
     The problem with the current methodology is that it does not control for different numbers of 16S gene that may exist in different microbes, PCR bias whereby sequences from different microbial species may be amplified at different rates, and sequencing bias where sequences from different microbial species may be sequenced at different rates. The result is that there is a lot of uncertainty with respect to the accuracy of relative abundance data derived using current methodologies. 
     The counting of different species may be based on the presence of a species in a single well. This is directly related to a single microbe from the original sample partitioning into the well during loading. Only PCR/NGS may be used to identify what microbial species exists in each well. The number of sequences identified does not form part of the calculation. Hence, it does not matter if there is PCR, NGS, or target sequence copy number variance or bias in the method. 
     Some embodiments may have applications in microbiome research, microbial product discovery and development, clinical diagnostics, and any other area where accurate counts of microbial species in a sample are required. 
     Accordingly, some embodiments may provide a much more accurate measurement of the relative abundance of each species in a microbiome sample, and the ability to convert this relative abundance measurement into an absolute abundance or a direct count of each species in the original sample (by accounting for the dilution and/or combining with a measurement of the total number of microbes in the original sample). Some embodiments may provide new applications for high density microfabricated chips (in addition to cultivation and screening of microbes). 
       FIG. 18  is a flowchart illustrating a counting method in accordance with some embodiments. In step  1800 , a sample is obtained. In step  1802 , at least one cell is extracted from the obtained sample. In step  1804 , at least one high density microwell array of a microfabricated device or chip is loaded with the at least one extracted cell. Step  1804  may include preparing a cell concentration with the at least one extracted cell, selecting at least one nutrient/media, and/or selecting at least one membrane. In step  1806 , at least a portion of the microwell array is sealed with the at least one selected membrane to retain the cell concentration with the microwells. In step  1808 , the chip is incubated. Step  1808  may include selecting a temperature, determining atmosphere (e.g., aerobic or anaerobic), and/or timing incubation). In step  1810 , the cultivated cells may be sacrificed for identification. Step  1810  may include PCR, sequencing, and/or various data analytics. In step  1812 , information about the sample (e.g., a microbial community structure) may be assessed and/or determined. 
       FIG. 19  is a diagram illustrating a counting method in accordance with some embodiments. Panel  1900  shows examples of complex samples, specifically a microbiome sample  1902  and a soil sample  1904 . In Panel  1906 , at least one cell is extracted from the sample using, for example, the protocol illustrated in  FIGS. 5A and 5B . In Panel  1908 , the at least one extracted cell (and any environmental extract and/or dilutant) is loaded on a microfabricated device or chip with at least one high density microwell array  1910 . Chip  1910  and a reagent cartridge  1912  may be loaded into an incubator  1914 . The reagent may be useful for adding liquid to maintain nutritional requirements for growth and/or various screening purposes. Panel  1916  shows the output: sequences and relative abundance of cultivated cells. 
     Droplet-Based Platforms 
     A discrete droplet-based platform may be used to separate, cultivate, and/or screen in much the same way that chips are used. A droplet is an analog of a microwell serving as a nano- or picoliter vessel. Droplet generation methods, especially when combined with cell-sorter-on-a-chip type instrumentation, may be used to separate out microbes from a complex environmental sample. Droplet addition may be used to feed microbes. Droplet splitting may be used for sequencing or some other destructive testing while leaving behind a living sample. All the prep work necessary for sequencing may be done in droplet format as well. 
     Some embodiments may be used to get microbes out of a complex environment and into droplets. For example, a modular system for generating droplets containing cell suspensions may contain one or small numbers of cells. The aqueous drops may be suspended in a nonmiscible liquid keeping them apart from each other and from touching or contaminating any surfaces. Droplets may be generated at, for example, 30 Hz in each microchannel, which translates into millions per day. 
     A drop-based microfluidic system may encapsulate, manipulate, and/or incubate small drops (e.g., about 30 pL). Cell survival and proliferation is noted to be similar to control experiments in bulk solution. Droplets may be produced at several hundred Hz, meaning millions of drops can be produced in a few hours. A simple chip-based device may be used to generate droplets and the droplets may be engineered to contain a single cell. 
     Some embodiments may be used to screen cells in droplets. Fluorescence screening of droplets post-incubation may be done on-chip and at a rate of, for example, 500 drops per second. Droplets may be flowed through a channel at the focus of an epifluorescence microscope that may be configured for a number of different measurements. This may be a particularly effective way to do screening for metabolites as the local concentration is quite high on account of being confined to a very small droplet. 
     Some embodiments may be used to sort droplets. Once cells have been isolated, grown, and/or screened, they may be sorted so that useful samples may be retrieved. Droplets may be sorted in an analogous way to the commonly used FACS machine. 
     Some embodiments may be used to split droplets. Some embodiments may require the ability to take a sample and split it in order to send one portion to sequencing (a destructive process) and retain another portion that is a viable culture. There are a number of different ways to split droplets including, but not limited to, constructing T-junctions with carefully calculated dimensions that result in drops splitting as they flow by or electrowetting (taking care not to cause cell lysis with voltages that are too high). 
     Some embodiments may be used to merge droplets and/or add a reagent to a droplet. For example, long term incubation of cells (e.g., weeks) requires the ability to add liquid to maintain nutritional requirements for growth. It also may be useful to be able to add reagents for various screening purposes. Droplet screening relies on being able to merge a droplet containing a compound-code with a droplet containing a single cell. The droplets then may be incubated and/or returned to an assay chip to identify compounds via their codes. This may require the ability to precisely merge drops on an as-needed basis. 
     Some embodiments may be used to perform PCR in droplets. PCR may be used in order to ultimately sequence a specific genetic element (e.g., the 16S region) in order to identify microbes. This may be used to determine what type of microbe is growing in each well. In a droplet-based system this approach may be used to determine what microbe is present in each droplet as long as the correct primer sequence is designed to amplify the right region of the genome. 
     Some embodiments may be used to sequence DNA out of droplets (e.g., generated in the PCR step) and/or prepare DNA libraries. 
     Location Specific Tags for High Density Chips 
     A high density chip device having a surface with a high density of microwells may be used. Microbes from a microbiome sample may be diluted and applied to the device such that wells contain approximately one microbe per occupied well. The chip may be incubated such that the microbe replicates within the well and the resulting population represents a single species. A DNA-based locational indexing system may be used to determine what species is present in each well. This indexing system may involve having PCR primers preloaded into each well that contain addressing barcodes that identify the well, and a primer sequence targeted to a specific genetic element (e.g., 16S in the microbial genome) that provides species information. After incubation the microbial DNA may be released, the PCR primers may amplify the target bacterial DNA region, and the amplicons from the various wells on a chip may be pooled and then read by next generation sequencing. 
     The above locational indexing system may involve incorporating a different locational code for each well of the microchip, or multiple locational codes may be incorporated into each well such that the total number of codes required to code a specified number of wells is reduced. For example, if there are 100 wells in a chip it would require 100 codes if there is one code per well. The same chip could be coded with only 20 codes if two codes were read from each well (i.e., 10 coding for the x axis of the grid and 10 coding for the y axis). 
     An example of a PCR strategy to incorporate two codes per well is provided in TABLE 2. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Primers 
                 Amplified PCR Products 
               
               
                   
               
             
            
               
                 5′- CODE1- 
                 CODE1 - TARGETSEQUENCE- 
               
               
                 TARGETSEQUENCEPRIMER1-3′ 
                 CODE 2 
               
               
                 3′- TARGETSEQUENCEPRIMER2 - 
               
               
                 CODE2 - 5′ 
               
               
                   
               
            
           
         
       
     
     An example of a PCR strategy to incorporate three codes per well provided in TABLE 3. 
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Primers 
                 Amplified PCR Products 
               
               
                   
               
             
            
               
                 5′- CODE1- 
                 CODE1 - TARGETSEQUENCE- 
               
               
                 TARGETSEQUENCEPRIMER1-3′ 
                 CODE 2- ADAPTER - CODE3 
               
               
                 3′- TARGETSEQUENCEPRIMER2 - 
               
               
                 CODE2 - ADAPTER 5′ 
               
               
                 3′- ADAPTER′ - CODE3′ 5′ 
               
               
                   
               
            
           
         
       
     
     Three oligo primers are used to make a single PCR product. Advantages to this system using two oligos to put a multi-partite barcode on one end of the molecule may include, for example, reducing maximum length of oligos needed or making extra-long barcodes. 
     This approach can be generalized to incorporate n barcodes per reaction. The approach can also have different implementations such that the barcodes are on the same side of the target sequence region. NGS sequencing adaptors may be added, and the full sequence for the population of barcoded PCR products may be read using next generation sequencing. 
     In another implementation, a fixed code may be added to indicate sample number or plate number and allow pooling of multiple samples/plates in a run for two barcodes as shown in TABLE 4. 
     
       
         
           
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Primers 
                 Amplified PCR Products 
               
               
                   
               
             
            
               
                 5′- PLATEA - CODE1- 
                 PLATEA - CODE1 - 
               
               
                 TARGETSEQUENCEPRIMER1-3′ 
                 TARGETSEQUENCE- CODE 2 
               
               
                 3′- TARGETSEQUENCEPRIMER2 - 
               
               
                 CODE2 - 5′ 
               
               
                   
               
            
           
         
       
     
     In another implementation, a fixed code may be added to indicate sample number or plate number and allow pooling of multiple samples/plates in a run for three barcodes as shown in TABLE 5. 
     
       
         
           
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Primers 
                 Amplified PCR Products 
               
               
                   
               
             
            
               
                 5′ - PLATEA - CODE1- 
                 PLATEA - CODE1 - 
               
               
                 TARGETSEQUENCEPRIMER1-3′ 
                 TARGETSEQUENCE- CODE 2- 
               
               
                 3′- TARGETSEQUENCEPRIMER2 - 
                 ADAPTER - CODE3 
               
               
                 CODE2 - ADAPTER 5′ 
               
               
                 3′- ADAPTER′ - CODE3′ 
               
               
                 5′ 
               
               
                   
               
            
           
         
       
     
     Note that in all cases the position of the barcode in the sequence conveys information hence the CODE1, CODE2, and CODE3 barcodes do not necessarily have to be different from each other in a particular well. 
     Making oligos and printing chips using a single code coding system are high cost. For example, a 10,000 well chip requires 10,000 single barcodes and 10,000 separate printing cycles to place those barcodes into the wells on the chip. If a two-code system is used, then potentially only 200 barcodes are required with only 200 printing cycles to manufacture chips. This represents a significant saving in oligo cost, printing time and printing capital investment. 
     The use of dual barcoded PCR primers, followed by amplification and sequencing analysis, to provide locational data on DNA or DNA containing moieties randomly partitioned onto a microfabricated chip may have high utility and relatively low cost. 
       FIG. 20  is a diagram illustrating an indexing system in accordance with some embodiments. Microwell chip  2000  has N rows and M columns, thereby producing N×M unique indices. A location of a microwell in chip  2000  may be considered to have the coordinates (N, M). Each column has a common reverse primer sequence (e.g., R1, R2, R3, . . . RM), and each row has a common forward primer sequence (e.g., F1, F2, F3, . . . FN). For example, a unique tag targeted to a specific genetic element in, for example, 16S ribosomal ribonucleic acid (rRNA) may include forward primer sequence F515 and reverse primer sequence R806. Following PCR of chip  2000 , the presence of the targeted genetic element may be mapped back to a unique microwell of origin based on the presence of a forward primer sequence and a reverse primer sequence. For example, the presence of F515 and R806 directs a user to the microwell with coordinates (515, 806) in chip  2000 . 
     Variability Reduction for PCR Amplification Product Across Microwells Containing Bacteria 
     A DNA-based locational indexing system may be used to determine what species is present in each well. This indexing system may involve having PCR primers preloaded into each well that contain addressing barcodes that identify the well, and a primer sequence targeted to a specific genetic element (e.g. 16S) in the microbial genome that provides species information. After incubation the microbial DNA may be released, the PCR primers amplify the target bacterial DNA region, and the amplicons from the various wells on a chip are pooled and then read by next generation sequencing. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include limiting amount of PCR primer in the well during manufacture of the chip such that for the majority of possible sample DNA concentrations the amount of PCR primer will limiting in the DNA amplification reaction, hence the amount of PCR product produced will be less variable across wells. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include limiting the number of PCR cycles on the chip to less than 3 cycles, or less than 5 cycles, or less than 10 cycles or less than 15 cycles, or less than 20 cycles or less than 25 cycles or less than 30 cycles such that the amount of PCR product produced will be less variable across wells vs. a full cycle PCR amplification protocol. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include limiting the amount of nucleotides in the reaction mix so that the number of PCR amplicons produced is a more related to the amount of nucleotides than the amount of DNA in the original sample. Microwells with a large amount of target DNA will exhaust the nucleotides early in the cycling process while microwells with a small amount of target DNA will exhaust the nucleotides later in the cycling process, but produce around the same amount of amplification product. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include limiting the amount of nutrient available to microbes growing in the wells such that cells will replicate until the media is exhausted then stop replicating. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include placing a dye in each well that identifies PCR product such that the signal gets brighter as more PCR product is produced. The intensity of the dye during each PCR cycle may be monitored, and a sample may be taken from the well once the desired signal intensity is observed. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include using mixtures of hybridization beads covered with oligos complementary to each well-specific bar code to selectively hybridize amplified DNA from each well. Once the beads are saturated unbound DNA may be washed away releasing bound DNA from the beads. The amount of DNA from each well will then be normalized at the saturation limit of the beads. 
     Some embodiments for limiting the variability in the amount of PCR product across wells may include incubating chips for a long period of time such that the fast growing microbes rapidly fill wells and cease replicating, and the slower growing microbes gradually fill wells and cease growing once approximately the same number of cells are in the wells 
     In some embodiments, use of barcoded primers and next generation sequencing (NGS) within the context of the chip format and method may be used to identify which species is growing in which well on the high density microchip. When an approximately equal number of bacteria occupy each microwell in the chip, the signal from each well in the NGS data may be approximately the same. 
     For example, in a typical NGS run generating 12 million sequence reads, if 24 chips are sequenced in the run, each having 10,000 microwells, and there is the same number of bacteria per well, there is on average 50 reads per well. 
     However, different bacteria grow at different rates so it is likely that some wells have few bacteria and some wells will have many bacteria. This potentially skews the NGS run so much that the wells with few bacteria are not detected in the NGS analysis. 
     Hence, in the example of a typical NGS run generating 12 million sequence reads, 24 chips are sequenced per run, each having 10,000 microwells, half of which have 100 times more bacteria in them than the other half. The probability that the bacteria in the slow growing wells are detected is markedly reduced. In this case:
 
(10,000×24)/2×100=12,000,000  (1)
 
(10,000×24)/2=120,000  (2)
 
     The low frequency wells are represented at 1% of total. So of 12,000,000 reads in an NGS run 120,000 will be from the low frequency wells—i.e. average of 1 read per well. 
     To minimize the impact of this phenomenon novel methods need to be developed to help equalize the amount of PCR product across wells so that all wells are detected in the NGS run. 
     Silicon-Based Microwell Chips for Microbial Isolation, Growth, Screening, and Analysis 
     A microfabricated device or chip may be composed at least in part of silicon instead of or in addition to plastic, glass, and/or polymers to allow for electrical measurements on a well-by-well basis. For example, the walls of each well may be isolated to create microcapacitors. In another example, an FET in each well such that the gate surface is exposed to the contents of the well. Instead of a purely silicon-based chip, thin metal layers may be generated on top of an existing chip by plating, vapor deposition, and/or arc/flame spraying. This may add more functionality to a chip, utilize alternate methods of manufacture which may be cheaper and/or cleaner, and/or allow miniaturization for handheld and/or portable devices. 
     Some embodiments may allow for monitoring growth by electrical measurement. Impedance monitoring may be applied to measure microorganism (e.g., bacterial) growth. For example, impedance across a tube containing  Escherichia coli  ( E. coli ) is compared to cell counts therefrom in Ur et al., “Impedance Monitoring of Bacterial Activity,” 8:1 J. Med. Microbiology 19-28 (1975), which is incorporated herein by reference in its entirety. Measurements may be taken on other types of bacteria including  Pseudomonas, Klebsiella , and  Streptococcus  to demonstrate the effect is general. Wells may be filled with different media in order to test growth conditions across different formulations. 
     Some embodiments may allow for screening by electrical measurement. Electrical measurements may be made on a well-by-well basis allowing for screening. One example would be pH. There are a number of different ways to get a pH-dependent response from the gate of a device in a well including, but not limited to, ISFETs and pH-meters. An array of wells with embedded pH sensors may determine, electrically, which wells contain microbes that are producing acidic or basic metabolites. A simple example is screening for the production of lactic acid from lactose. Bacteria is diluted out into wells, grown, and then fed lactose. Wells that record a drop in pH contain microbes capable of metabolizing lactose into lactic acid. 
     Some embodiments may allow for electrical measurements of redox probes. Another way to leverage electrical measurements is to look at how bacteria in wells affect a known redox probe. Essentially, a system with well-defined response may be measured in the presence of bacteria and deviations from expected behavior may be attributed to the bacterial samples. A typical redox probe is something like ferricyanide; [Fe(CN)6]3−/4−. The reduction of ferricyanide to ferrocyanide is very well characterized such that small changes in behavior, particularly around electron transfer from the electrodes, are discoverable. This system is “label free” as it detects without having to directly modify the bacteria themselves. 
     Antibodies that can recognize microorganisms (e.g.,  E. coli ) may be immobilized on ITO electrodes. Electron transfer resistance may be measured from the electrodes to a ferricyanide containing solution.  E. coli  binding to the electrode surface increases the resistance proportional to the concentration of  E. coli  on the surface. This is one example of a family of measurements that may be made to detect specific types of organisms or metabolites using redox probes. 
     Working in silicon (or at least metals or metallized plastics) provides advantages including, but not limited to, less expensive production of chips (e.g., by piggybacking on existing technologies); integrated detection capability allowing small and/or portable versions; additional measuring capabilities not present in other materials (e.g., LCR, CV, etc.); integration of newly discovered chip-based detection modalities into existing devices; and the combination of electrical measurements and sequencing. These advantages would benefit any customer using interferometric detection. 
     Releasable Barriers to Protect Well-Specific Chemistries on a Chip 
       FIGS. 21A-21E  are diagrams illustrating a chip with well-specific chemistries in accordance with some embodiments. In  FIG. 21A , a microfabricated device or chip is shown with a plurality of microwells. In  FIG. 21B , microwell-specific chemistries have been disposed in each microwell of the chip. In  FIG. 21C , a sealant has been applied over the microwell-specific chemistries in each microwell of the chip, thereby preventing interaction of the chemistries with further additions to the wells. In  FIG. 21D , samples are loaded, and experiments are performed on the samples in the microwells. In  FIG. 21E , a trigger (e.g., heat) releases the microwell-specific chemistries for interaction with samples in the wells. 
     Microwell chips may be manufactured, be cleaned, and/or have surfaces treated. The specific chemistries may be prepared separately and then deposited into wells by, for example, using a method and/or device that allows a specific set of chemicals to be directed to a specific well (or wells). A sealant then may be applied to protect the various chemistries from the environment and/or be removed/released/disbursed with some defined, external trigger. 
     A microfabricated device or chip may be manufactured to a specific design, for example, cleaned and/or surface treated to improve wetting. PCR primers may be printed or pin-spotted into specific wells. The chip may be allowed to dry, and then a wax layer may be deposited by evaporation from an ethanol solution. Optimal concentration may be about 1% v/v. Molten wax may be applied directly or an aqueous or alcohol wax solution may be sprayed. Alternatively, spin coating or vapor deposition may be used. Various waxes may be used including, but not limited to, glyceryl stearate with and without polyethylene glycol, cetearyl alcohol, 1-hexadecanol, glyceryl ester of stearic acid, ceteareth-20 (CAS Registry No. 68439-49-6), and some commercial products including, but not limited to, Lotionpro™ 165 (available from Lotioncrafter®, Eastsound, Wash.) and Polawax™ (available from Croda, Inc., Edison, N.J.). The underlying chemistry later may be released by, for example, heating until the wax melts. For these compositions it will be between 50° C. and 70° C. It is important to be low enough not to damage any chemical component or to boil our aqueous solutions. 
     The key concept is of well-specific chemistry that is walled off from the chip until the experimenter triggers release. This method may be used for barcoding in wells, but it also may be applied more broadly to a whole range of different problems. Different chemistries that may be useful to seal on a chip include, but are not limited to, antibiotics, fluors, dyes, PCR primers, lysis-promoters, antibodies, and/or tests for various metabolites. While wax is a good way to seal things that can later be released by heating, other materials may be used to seal and release upon exposure to light, sonication, and/or some other trigger. The advantage of this method over simply adding reagents to the chip is one of control on a well-by-well basis. A similar effect might be achieved by printing chemicals into wells after doing microbial experiments, but this introduces problems with time (the print run may be as long as a day) and the fact that it is impossible to expose every well for the same amount of time if each well is filled individually after the microbes are on the chip. With a release mechanism every well can be exposed at the same time. In one example, wax may be deposited onto chips by solvent casting. 
     Isolated Microwells for Simplicity and/or Controlling Relative Abundance 
     A high-density chip device may comprise a surface having high-density microwells. Microbes from a microbiome sample, or other cell types, may be diluted and applied to the device such that wells contain approximately one microbe or cell per occupied well. These microwells may be sealed with semi-permeable membranes that allow nutrients to diffuse into the microwells but prevent all or at least some of the microbes or cells from moving out of the microwells. 
     A sample of microbes or cells may be prepared and then sealed into a chip using an impermeable or only-gas-permeable membrane. No reservoir of liquid sits on top of the chip or membrane and hence only the nutrient in the well at the time of sealing is available to support growth of the microbes or cells in the microwell. Two reasons for this feature include: (1) simplicity in construction and workflow as the device need not have semi-permeable membranes or reservoirs, nutrients do not have to be added, and there is less potential for contamination; and (2) a check on the relative abundance of fast-growers by limiting their access to nutrients. For a sample containing some fast-growers and some slow-growers, the fast-growers will rapidly be resource-limited in their respective microwells and stop or slow growth while the slow-growers continue to grow. This provides for slow growers to be represented at a higher relative abundance in the population of microbes across the chip, compared to the case where the fast growers do not have a limiting amount of nutrient. This becomes important for downstream processing when sequencing everything on a chip. It also provides a better detection limit for rare species as the rare species are not outgrown by fast growing species to a point that limits the ability of the system to detect them. 
     Current methods attempt to get all species to grow whether they are fast- or slow-growing by nature. This has the inevitable result that fast-growers dominate communities and only increase in relative abundance with time. Many types of downstream analysis such as sequencing or fluorescence screening cannot resolve every species in a given population but only those above a certain limiting relative abundance. If the goal is to preserve diversity and detect rare species, then the fast-growers need to be limited in some way. 
     For an example that demonstrates this idea, consider the simple case of a sample containing two species: one doubles every day and the other doubles every week as shown in TABLE 6. If the slow-grower is rare to begin with, at 5% relative abundance, it soon becomes very rare as both species grow. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Unlimited 
                 Day 0 
                 Day 1 
                 Day 2 
                 Day 3 
                 Day 7 
                 Day 14 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Fast grower 
                 19 
                 38 
                 76 
                 152 
                 2432 
                 311296 
               
               
                 Slow grower 
                 1 
                 1 
                 1 
                 1 
                 2 
                 3 
               
               
                 Total 
                 20 
                 39 
                 77 
                 153 
                 2434 
                 311299 
               
               
                 Rel. ab. fast 
                 0.950 
                 0.974 
                 0.987 
                 0.993 
                 0.999 
                 1.000 
               
               
                 Rel. ab. slow 
                 0.050 
                 0.026 
                 0.013 
                 0.007 
                 0.001 
                 0.000 
               
               
                   
               
            
           
         
       
     
     If the fast-growers are limited by competition for nutrition and/or physical space to grow, then the relative abundance of the slow-growers will start to increase after some time has elapsed as shown in TABLE 7. 
                                             TABLE 7               Limited   Day 0   Day 1   Day 2   Day 3   Day 7   Day 14                                                            Fast grower   19   38   50   50   50   50       Slow grower   1   1   1   1   2   3       Total   20   39   51   51   52   53       Rel. ab. fast   0.950   0.974   0.980   0.980   0.962   0.943       Rel. ab. slow   0.050   0.026   0.020   0.020   0.038   0.057                    
High Density Microfabricated Arrays for Biobanking Cells
 
     Biobanks are designed to give researchers access to a large number of samples from a large population in order to drive certain types of research, such as disease-related biomarker discovery. The current state of the art in biobanking provides for samples to be stored in tubes or low-density plate format such as a 96-well or 384-well plate. This works when the number of samples to be stored is relatively low in number and the samples themselves are discrete, isolated populations. Current approaches to biobanking become very cumbersome when storing samples, such as microbiome samples, where the number of samples may be high and the number of different species or variants in each sample may extend from hundreds to thousands or many millions per sample. Using current methods, a laborious isolation protocol must be implemented to separate out individual species or variants either prior to or subsequent to the storage step in order to access a desired species or variant. 
     The systems, kits, apparatus, and methodologies described herein may be applied to biobank cells, microbes, viruses, and other biological entities. A high-density chip device comprised of a surface having high density microwells may have thousands, hundreds of thousands, or millions of microwells per chip. For example, microbes from a microbiome sample (or another biological entity such as a different type of cell or a virus) may be diluted and applied to the device such that wells contain approximately one microbe per occupied well. The chip then may be incubated such that the microbe replicates within the well and the resulting population represents a single species. A nucleic acid-based locational indexing system may be utilized to determine what species is present in each well. This indexing system may involve having PCR primers preloaded into each well. The PCR primers may contain addressing barcodes that identify the well, and a primer sequence targeted to a specific genetic element (e.g., 16S) in the microbial genome that provides species information or targets a desired genetic sequence. After incubation the microbial DNA is released, and the PCR primers amplify the target bacterial DNA region. The amplicons from the various wells on a chip may be pooled and then read by next generation sequencing. 
     Using high-density microfabricated chips for biobanking provides for a multitude of species or variants within each sample to be stored as separate populations without the need to implement a laborious isolation protocol either before or after storage. Using the DNA-based locational indexing system or a custom assay enables a simpler, generic approach to identifying genetic signatures or characteristics of the contents of each microwell to give information such as, for example, species information. Additionally, the chip devices provide for an extremely space effective method of storing cell isolates. For example, a single microscope slide dimensioned chip with 100,000 wells occupies substantially less space that the corresponding traditional storage formats. The chip format also may be useful for properly archiving and curating samples and/or for managing subject (e.g., patient) information databases by having one chip contain many different samples from a single subject. 
     In order to bank cells using this apparatus, cells may be disposed and/or positioned in microwells of the apparatus. The cells in the microwells may be treated to ameliorate the impact of storage then placed in appropriate storage conditions. For example, cells may be treated with agents such as glycerol to ameliorate the impact of freezing. Then the chip may be placed in appropriate storage conditions such as a freezer. The cells may be dehydrated, lyophilized, and/or freeze dried, and the chip may be placed in appropriate conditions to safeguard the dried cells. Additional structures may be added to the chip to further enhance its utility as a storage device. For example, a membrane or another structural element may be placed on top of the chip to seal at least some of the wells prior to storage. 
     A chip may be loaded with cells such that a portion of microwells on the chip are occupied by approximately one cell each. The chip is incubated to allow for replication of cells. The chip and its contents are substantially replicated, and either the original chip or the copy chip is used to identify the cells or species or gene signatures present in each well of the chip (by, e.g., using the locational indexing system described above). The chip is treated and/or stored in appropriate conditions. The replication step and/or the identification step may take place after storage rather than before storage. 
     One or more cells from each strain of a pre-existing set of isolated strains may be disposed into separate microwells on a chip. The position of the microwell into which each strain or cell type was placed may be recorded, and the chip may be treated and/or stored in appropriate conditions. 
     A version of the chip may be created in which preservative chemistry is sequestered underneath a wax barrier in each well. Isolates may be allowed to grow sealed up inside a chip and then preserved at a later date by heat-induced release of the preservatives before banking. 
     Such apparatus may be used to store/biobank mixed microbiome samples such as microbiome samples from soil, human gut, seawater, oral cavity, skin, etc. A chip may be used to store other types of biological entities such as fungi, archaebacteria, human cells (including reproductive cells), animal cells, and viruses. 
     The DNA locational indexing system may be used across all biological entity types to generate information regarding the content of each well. An entire chip may be screened for desired activity using custom assays such as antibody- or substrate-based assays. For example, a chip with banked populations of T cells may be screened for a particular immunological activity. 
     In one illustrative example, human stool microbiome samples may be collected from study participants. The stool microbes from each individual may be biobanked on chips to maintain both a record of that individual&#39;s microbiome as well as a sample of the microbiome to use as a source of target microbes at a later date. In another example, mixed populations of T cells or other immunological cells may be sampled from individuals during clinical or research studies or as part of a therapeutic workflow (e.g., cell therapy using ex vivo treated cells). In yet another example, soil biomes may be stored in conjunction with seed banking. 
     High Resolution Picking 
     A high accuracy/precision picking apparatus or system may be designed to execute various picking functions from and/or to microwells on a microfabricated chip described above. A target substrate or chip may be a microscope slide format (approximately 25 mm×75 mm×1 mm) with injection-molded features on one surface. Microwells may be arranged in a grid pattern with about 4-8 mm well-free edge around the edges of the chip. Well size and spacing may be determined based on picker capability. Microwells may be square with a size from about 25 μm to about 200 μm along each edge and spacing in from about 25 μm to about 100 μm between well edges. Microwells may be circular or hexagonal instead. Well depths may be from about 25 μm to about 100 μm. For example, a 75 mm×25 mm slide with a 7 mm edge, 100 μm square wells with 100 micron edge-to-edge spacing will have about 16,775 microwells. 
     A high accuracy/precision picking system may be designed to execute various picking functions from and/or to portions of a membrane corresponding to microwells on a microfabricated chip, as described above. A membrane may be a thin sheet that has previously been used to seal growing bacteria into microwells. When peeled off the chip the membrane may retain an imprint of the microwell array as well as a sample of bacteria on its surface after separation from the chip. Thus, the peeled membrane may act as a replicate of the bacteria growing in the chip. 
     A high resolution picker may receive data input from a user. The input may include at least one pair of chip microwell coordinates such that the picker picks from and/or to the at least one input pair of coordinates. A sterilization routine may be performed between cycles. A high resolution picker may be capable of operating in an anaerobic chamber. 
     A high resolution picker system may receive a chip and align the picker with the chip, for example, using fiducial markers and/or reference wells. The picker may pick, for example, cells growing in microwells on the chip into, for example, 96- or 384-well plates containing growth media. The picker may include a single picking pin or a plurality of picking pins. 
     A high resolution picker system may receive a membrane and align the picker with the membrane, for example, using reference well marks on the membrane. The picker may pick, for example, cells from the membrane into, for example, 96- or 384-well plates containing growth media. The picking pin(s) may have a different shape (e.g., mushroom-shaped) and/or surface (e.g., texture) for picking from a membrane. The system also may include one or more mechanisms (e.g., a floating pin and/or vacuum) to hold and/or flatten the membrane. 
     A high resolution picker system may enable chip replication via a chip-to-chip transfer. The picker may receive and align a first chip based on fiducial markers and/or reference wells. The picker also may receive and align a second chip based on fiducial markers and/or reference wells. The picker may transfer, for example, cells growing in microwells on the first chip to microwells on the second chip. 
     A high throughput system for automatically picking a target species of a plurality of species of at least one biological entity cultivated in a microfabricated device may include a port for receiving the microfabricated device. The microfabricated device defines a high density array of microwells. Each microwell of the high density array of microwells is configured to isolate and cultivate at least one species of the at least one biological entity and includes at least one tag of a plurality of unique tags. Each tag of the plurality of unique tags includes a nucleic acid molecule, which includes a target-specific nucleotide sequence for annealing to the at least one biological entity and a location-specific nucleotide sequence correlating to at least one microwell of the high density array of microwells. The system also includes a high-resolution picking apparatus with at least one protrusion for picking the at least one biological entity from at least one microwell of the high density array of microwells. The system further includes an input device for receiving an indication of at least one target-specific nucleotide sequence and at least one processor communicatively coupled to the input device and the high-resolution picking apparatus. The at least one processor acquires the indication of the at least one target-specific nucleotide sequence from the input device, compares the at least one target-specific nucleotide sequence to the plurality of unique tags, determines at least one microwell of the high density array of microwells including the target species based on the comparison, and controls the high-resolution picking apparatus to pick the at least one biological entity from the at least one determined microwell of the high density array of microwells. 
     A high throughput system is disclosed for automatically picking a target species of a plurality of species of at least one biological entity cultivated in a microfabricated device. The microfabricated device defines a high density array of microwells, each microwell of the high density array of microwells being associated with at least one unique primer of the plurality of unique primers. The system includes a port for receiving a membrane removed from the microfabricated device, the membrane having sealed each microwell of the high density array of microwells to retain the at least one biological entity in the high density array of microwells, such that portions of the at least one biological entity corresponding to the high density array of microwells remain attached to the membrane following removal of the membrane. The system also includes a high-resolution picking apparatus including at least one protrusion for picking the at least one biological entity from at least one membrane location corresponding to at least one microwell of the high density array of microwells, an input device for receiving an indication of at least one target-specific nucleotide sequence associated with the target species, and at least one processor communicatively coupled to the input device and the high-resolution picking apparatus. The at least one processor acquires the indication of the at least one target-specific nucleotide sequence from the input device, compares the at least one target-specific nucleotide sequence to the plurality of unique tags, determines at least one membrane location corresponding to at least one microwell of the high density array of microwells comprising the target species based on the comparison, and controls the high-resolution picking apparatus to pick the portions of the at least one biological entity from the at least one determined membrane location. 
     The above-described embodiments can be implemented in any of numerous ways. For example, embodiments may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers. 
     Further, it should be appreciated that a computer may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Additionally, a computer may be embedded in a device not generally regarded as a computer but with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smart phone or any other suitable portable or fixed electronic device. 
     Also, a computer may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible format. 
     Such computers may be interconnected by one or more networks in any suitable form, including a local area network or a wide area network, such as an enterprise network, and intelligent network (IN) or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks. 
     The various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine. 
     Bacterial Community Relationship Determination 
     In some embodiments, the systems, kits, apparatus, and methods described above may be used to determine bacterial community relationships. The microwell array on the microfabricated device (or chip) with locational indexing system described herein (e.g., by placing in each microwell oligonucleotides containing coding information that identifies their specific microwell, as well as a primer sequence that targets a nucleic acid sequence) may be used to analyze syntrophic or other types of inter variant or inter species relationships in a microbiome sample in a massively parallel way. 
     In accordance with some embodiments of the present invention, a method of analyzing a sample including a population of biological entities is provided. The method utilizes at least one microfabricated device having a top surface defining an array of microwells, wherein a plurality of the microwells of the array of microwells each comprise a unique tag nucleic acid molecule including: (1) a target-specific nucleotide sequence for annealing to a target nucleic acid fragment of one or more biological entities of interest that may be present in the microwell, and (2) a location-specific nucleotide sequence for identifying the location of the microwell on the microfabricated device. In the method, a sample is loaded onto the microfabricated device such that at least some microwells of the plurality of microwells each include more than one cell of a biological entity. An amount of a nutrient is also loaded into each of the plurality of microwells. This can be done as a separate step, or the nutrient and the biological entities can be loaded together simultaneously. The microfabricated device with the loaded microwells is incubated at predetermined conditions. Then amplification is performed on-chip in each individual microwell of the plurality of microwells, e.g., by performing an PCR amplification on a selected genetic material of the cells of the biological entities (such as genomic DNA of bacteria, fungi, or eukaryotic cells) obtained from the incubation, thereby obtaining first amplicons in the plurality of microwells. It is possible that the amplification may not be successful in each and every microwell where the amplification is performed. The first amplicons are collected/pooled from the plurality of microwells, and sequenced to obtain sequencing data. Based on the sequencing data and the unique tag nucleic molecule included in each of the plurality of microwells, the biological entities present in at least a subset of the plurality of microwells is identified. In some embodiments, based on the identification of the biological entities present in each of the plurality of microwells, a presence or absence of a relationship is determined between at least two different types of biological entities in the population of biological entities contained in the sample. The relationship can be a dependent relationship, a symbiotic relationship, or a destructive relationship. The presence or absence of a relationship can be determined by comparing across the plurality of microwells which types of biological entities are present or not present in the same microwells after incubation. 
     For example, cells isolated from a complex microbiome sample (i.e. containing one or more species or variants) can be distributed into microwells of a microfabricated device with proper dilution and a distribution method that results in, on average, more than one cell per microwell. The distribution method could, for example, be by applying a solution containing microbes onto the array such that microbes are randomly distributed into microwells. The concentration of microbes in the solution can be adjusted to target a desired average number or distribution of bacteria per microwell. Alternatively, microbes could be placed directly into microwells with a device such as a cell sorter. 
     The target average number of cells per microwell can be varied depending on the number of the microbes in the sample and the complexity of the dependence being assessed. For example, it may be two cells per microwell, 5 cells per microwell, 10 cells per microwell, 50 cells per microwell, 100 cells per microwell, or other number of cells per microwell. In some embodiments, the average number of cells per microwell is between 2 and 20. In other embodiments, the average number of cells per microwell can be between 5 and 50, between 10 and 100, etc. As the distribution method may have variations, there may be microwells with no cells in them, some microwells with one cell in them and some microwells with more than the desired number of cells in them. 
     In embodiments of the method, the population of biological entities in the sample comprise bacteria. The bacteria can include bacteria of different strains, different species, or different genera. The population of the biological entities can include a collection of microorganisms naturally occurring in a specific environment. For example, the biological entities can be a collection of microorganisms obtained from a human stool, human gut, human skin, human nasal cavity, vagina, soil, rhizosphere, water, etc. In some other embodiments, the biological entities can include eukaryotic cells. 
     After loading on the microfabricated device, the cells can be cultivated by incubating the microfabricated device at suitable conditions. The incubation can be performed in various ways. For example, prior to incubation, a membrane can be applied on the top surface of the microfabricated device to retain the cells loaded in the microwells. The nutrient can be pre-loaded in the microwells and retained by the membrane. In some embodiments, the nutrient can be loaded in a reservoir provided on the membrane and external to the microwells. The membrane is permeable to the nutrient and allows the nutrient to migrate from the reservoir into the microwells. 
     After incubation, the microfabricated device can be replicated or split as described previously to make a replicate of the contents of the microwells by removing a small sample from each microwell. On-chip PCR or other means of nucleic acid amplification can then be run to generate libraries of amplification product or amplicons with appropriate indexing such that one can generate a list of the cell contents (genus, species, strains, variants or other) of each microwell for analysis. 
     By observing which genus, species, or other types of microbes grow with each other in the same microwells across the array of microwells of the microfabricated device, potential dependencies or relationships that exist within that microbiome can be determined. For example, the relationship can be a dependent relationship, a symbiotic relationship, an inhibiting relationship, or independence. For illustration, a dependent relationship between two species is one where one or both species are dependent upon the other in order to survive, thrive or proliferate. When both species depend on each other to survive, thrive or proliferate, they are considered interdependent. In the case where the first species is dependent upon the second, it will be for the most part only detected growing in the presence of the second species. In the case where the first and second species are dependent upon each other, neither species will be found growing in the absence of the other. A symbiotic relationship between two species is where a first species can survive, thrive or proliferate in the absence of a second species, but grows or proliferates more favorably in the presence of the second species. An inhibiting or destructive relationship between two species is one where one species inhibits the growth of or kills the second species. If a first species is inhibited by the second species, then the first species will not be detected, or only be detected at low levels whenever the second species is present. Independence (or lack of a relationship, absence of a relationship) between two species refers to the situation where both the first and second species are able to grow successfully both together and separately. Both the first and second species will be detected growing both together and separately. 
     One could employ various abundance thresholds to analyze the result from the microwells to determine the potential relationship between the two species. For example, one could consider an abundance of a first species of less than 1% to be equivalent to zero; or an abundance of a first species of less than 5% to signify inhibition. The exact nature and level of the cut-offs will vary between different biological systems and compositions. The method can be used to analyze inter species relationships across an entire microbiome containing many hundreds or thousands of different components/species/variants. 
     Consider a community with two elements or species A and B. They are loaded on a chip, grown, and then indexed and sequenced. The sequence data can be studied to determine which species grows with which other species and therefore provides insights into their relationships and dependencies. If A and B can coexist, the expected result is some microwells with A without B, some with B without A, and some with both A and B. If A destroys B, then there will be multiple instances of A, multiple instances of B and minimal or no instances of A+B. If A and B has a true mutual symbiotic relationship and there will be multiple examples of A+B and minimal or no examples of A or B alone. 
     More particularly, to determine a relationship between cells of two biological entities of interest, say Microbe A and another microbe (Microbe B, Microbe C, etc.), in a microbiome sample, the following example procedure can be used. The procedure is only illustrative and does not limit the invention. 
     1. Take the sample, such as soil. 
     2. Separate the microbial cells in the soil from the rest of the soil to produce a suspension of microbial cells. This can be done by filtering and centrifugation using a medium such as nycodenz. 
     3. Count microbial cells in the suspension using techniques such as counting cells in a cell counting slide (such as a haemocytometer) under a microscope or with a flow cytometer. 
     4. Take an microfabricated device as described herein, where each microwell is preloaded with a PCR primer that incorporates i) a barcode nucleotide sequence that are specific to the individual microwell (e.g., the row and column number of the microwell, or other relative location of the microwell on the microfabricated device), and ii) a nucleotide sequence that targets the 16S rRNA gene region of the bacteria. (For analysis of microbiome comprising fungi, the nucleotide sequence can be targeting ITS gene region) The primers can be protected by a wax coating. Both the primers and the wax can be printed into the microwells using high resolution printing devices. 
     5. Dilute the cell suspension so that when loaded onto an microfabricated device of the present invention, the expected (or average) number of cells per occupied microwell is 5. Some microwells can have fewer than five cells and some can have more. The cells can be suspended in appropriate growth media. 
     6. Load the microwells by pipetting the dilute cell suspension on the surface of the microfabricated device such that all microwells are covered with liquid. A portion of the bacterial suspension enters the microwells. 
     7. Either: (a) place an impermeable or a gas permeable membrane over the microwells, or (b) place a permeable membrane over the microwells, then a nutrient reservoir with nutrient. 
     8. Incubate the microfabricated device for a period and at suitable conditions (temperature, humidity, atmosphere, etc.) appropriate to the species being studied. 
     9. Replicate the microfabricated device using methods described herein. Add membrane to one or both replicates, and optionally incubate some more. 
     10. Take the replicate of the chip containing the PCR primers, immerse in liquid nitrogen then remove from liquid nitrogen, then remove membrane and add a PCR mix to the microwells, cover the microwells with oil and perform on-chip PCR by amplifying genomic DNA of the bacteria in a flatbed PCR thermocycler. 
     11. Pool the PCR products or amplicons from the microwells on the chip, and add sequencing adaptors and sample specific barcodes for a second PCR reaction. 
     12. Sequence the amplicons in a Next Generation Sequencing system such as Illumina Miseq. This can give a read out of the majority of the location-specific barcodes on the microwells and the 16S sequence will indicate which microbes are growing in which microwells. Given the nature of 16S analysis this information will generally be at the genus or species level. 
     13. Analyze results to determine what species or genera grew in each microwell. 
     14. Identify those wells containing Microbe A. Identify for each microwell containing Microbe A what other species are growing in the same microwell. As there are a limited number of species in each well it is possible to identify which additional species may support the growth of Microbe A. For example, the result may be that Microbe A only grows in the presence of Microbe B, Microbe C or Microbe D. 
     15. The experiment can be repeated using a higher dilution level to target only 2 microbes per well—this can provide confirmatory information. 
     The method described above can be used to map relationships across an entire microbiome, including i) what species always grow with other species (indicating dependency (including interdependency)), ii) what species never grow with certain other species (indicating destructive or inhibiting relationship), iii) what species are able to grow independent of other species. This data can be used to create a map of relationship across the entire microbiome and identify clusters of microbes sharing interdependent relationships. This information can be used, for example, to predict which microbes in a microbiome sample may be easy to cultivate (because they grow independently) and which microbes may be difficult to cultivate independently as they depend on other species for critical growth factors. 
     The above method can also be used as a discovery tool for novel antibiotics. For example, microfabricated chips are loaded such that any one of microwells thereon containing only one species is mathematically unlikely, e.g., by dilution to a predetermined concentration or using a cell sorter to apply the microbes in solution to the microwells on the array. If any microwell contains only one species, the species is likely to produce antibiotics (i.e., it is likely that other species which were previously in the microwell have been killed by an antibiotic secreted by the surviving species). A viable sample of the putative anti-biotic producer can be amplified and further tested via splitting of the chips. 
     Different microbial growth media can be used on the array to understand the effects of media formulations (or nutrients) on relationships between bacterial variants or species, e.g., promoting or retarding any interdependent relationship, and the underlying chemistry for such effects. For example, multiple microfabricated devices containing different media formulations or nutrients can be loaded with microbes from a microbiome sample and processed as outlined above. Differences in the growth dependency map observed between arrays would indicate how each media influence syntrophic relationships or other interactions between different bacterial variants or species. Medium X may be formulated such that it has no free amino acids. Medium Y may be formulated such that is it the same as Medium X but contains free amino acids. Suppose one finds that Species A only grows in the same microwells as Species B when using Medium X, but Species A can grow independent of Species B when using Medium Y. This suggests that Species A may require amino acids secreted by Species B to grow. Using multiple formulations of media and analyzing across all microwells a map of syntrophic relationships and an indication of the underlying nature of these relationships can be developed for the microbiome. 
     Alternatively, different media formulations can be added into microwells located on different sub-area of a single microfabricated device and inoculated with the particular microbial species or microbiome under study. Differences in observed growth dependencies due to different media will provides insights into the underlying nature of the relationship. 
     Further, the effects of different media formulation on the bacterial relationships as well as individual bacterial growth can be determined. For example, relationships within a microbiome of interest can be studied according to the method described herein and it is determined that microbe G only grows in the presence of microbe K with a given growth medium. The microbiome can be reanalyzed using a number of different media on different microfabricated chips. It is determined that for a certain media formulation, microbe G is able to grow in the absence of microbe K. Then, this particular media formulation is deconstructed and the various components used in further experiments to determine which component facilitates the growth of microbe Gin the absence of microbe K. 
     Alternatively, the above can be accomplished in the following manner: Relationships within a microbiome of interest are studied and it is determined that microbe G only grows in the presence of microbe K with a given medium. An array is then made such that different media formulations are placed in different microwells on the array. This may be performed by, for example, using a highly accurate printing device such as an inkjet printer to deliver different media formulations in different wells. Then the array is loaded with a mixture of microbe G and microbe K. The above-described locational indexing system can then be used to determine in which microwells i) only G grows, ii) only K grows, iii) neither G nor K grows, or iv) both G and K grow. Such growth information is correlated with the media formulation and used to infer what components may be important in the growth relationship. 
     While theoretically the above studies of microbial interrelations may be done on traditional platforms (e.g., petri dishes), using the microfabricated chips with arrays of microwells of the present invention allows such studies to be done in a massively parallel manner and in a highly multiplexed format, which does not require any a priori knowledge of how each species will behave. A single experiment or a small number of experiments can enable the identification of a large number of relational dependencies in a complex microbiome. Coupled with the ability to sample each well (by replicating the contents of the microwells) before getting sequence data to build the relationship map, if any relationship of interest is discovered, the sample in which such a relationship is discovered could have already been replicated, allowing a viable sample of the microbe to be reserved for further experimentation. 
     In the following examples, each microwell on a panel consisting of 2500 (50×50) microwells (each is square with edges of 100 μm by 100 μm and 100 μm deep) of a microfabricated chip is loaded with a unique tag oligo which serve as PCR amplification primers directed to the 16S bacterial gene region. Each tag oligo includes a barcode sequence to identify the specific location of the microwell in which the tag oligo is loaded. The microwells are arranged in a grid pattern, therefore the barcode sequence herein includes a subsequence to identify the column of the microwell and another subsequence to identify the row. 
     The methods used are as follows: 
     Chip PCR Protocol 
     1. Diluted the bacteria in TSB medium 1:10. 
     2. Loaded 3 μL bacteria into each panel of the chip and seal with PCR sealer. 
     3. Incubated the chip with bacteria at 30° C. incubator overnight. 
     4. Immersed the chip in liquid nitrogen to facilitate lysis 
     5. Removed seal. 
     6. Loaded 3 μL chip PCR buffer, and sealed the chip with PCR sealer. 
     7. Loaded the chip in Life Tech QuantStudio 3D Digital PCR System and run the chip PCR. PCR amplification protocol: 96° C. 12 min; 39 Cycles for: 60° C. 2 min, 98 C 40 sec; 60° C. 2 min; 10° C. hold. 
     8. NGS library building: in order to add the sample index and NGS adaptor for each chip sample, a second PCR amplification was run to prepare the NGS library. After confirming presence of the right products with gel electrophoresis, the amplicon was purified with Kapa purification beads, and a final aliquot of 25 μL of amplicon product was collected for NGS. 
     Illumina MiSeq and Bioinformatics 
     1. Loaded 10 pM DNA library on the MiSeq and ran the NGS 
     2. Demultiplexed the data using the unique tag information and located each NGS read to each microwell of the microfabricated device. NGS read data were thresholded to 5000 reads per well. 
     The panel of microwells was loaded with an 8 species mock community of live bacteria and incubated overnight. The mock community consisted of  Acinetobacter calcoaceticus, Bacillus cereus, Bacillus subtilis, E. coli, Pseudomonas aeruginosa, Salmonella enterica, Serratia marcences  and  Staphylococcus warneri . After chip PCR and NGS as described above, the NGS data show that there were total NGS reads of about 7,514,030. Bacteria were detected in 1503 microwells (about 60% of all microwells in the panel). In 92% of these microwells multiple bacterial genera were detected. In 108 microwells a single bacterial genus was detected, the majority of which were  E. coli . There were also microwells that each contain multiple species where  E. coli . was the most abundant species in these microwells. One of the explanation is  E. coli  grown quickly and occupy major of the wells. To understand the distribution of number of bacterial genera grown in each microwell, the data were summarized and shown in  FIG. 22 . There were 108 wells that had single genus bacteria detected, 426 wells that had two bacteria genera detected, 334 wells that had three genera detected, and 635 wells that had 4 or more genera detected. 
     While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. 
     Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. 
     All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. 
     All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. 
     The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” 
     The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. 
     As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. 
     As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. 
     In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “defining,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.