# Patent

## Title
Host cell modification with artificial endosymbionts

## Abstract

The present invention is directed generally to host cells with artificial endosymbionts, wherein the artificial endosymbiont and the host cell communicate with each other to alter a phenotype of the host cell. In some embodiments, the communication comprises the secretion of a polypeptide from the artificial endosymbiont into the host cell. The secreted polypeptide can be a selectable marker, a reporter protein, a transcription factor, a signal pathway protein, a receptor, a growth factor, a cytokine, an effector molecule or other factors that can produce a phenotype in the host cell.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. Ser. No. 14/476,584 filed Sep. 3, 2014, which claims benefit of U.S. Provisional application Ser. No. 61/873,308, filed Sep. 3, 2013, all of which are incorporated by reference in their entirety for all purposes.


REFERENCE TO SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM
The official copy of the Sequence Listing is submitted concurrently with the specification as an ASCII formatted text file via EFS-Web, with a file name of “BELL.018_ST25.txt”, a creation date of Sep. 3, 2014, and a size of 962 kilobytes. The Sequence Listing filed via EFS-Web is part of the specification and is hereby incorporated in its entirety by reference herein.
TECHNICAL FIELD
The present invention relates generally to host cells with artificial endosymbionts. The artificial endosymbionts of the host cell communicates with the host cell and changes aspects of the host cell.
BACKGROUND
The advent of recombinant DNA technology created the ability to alter the genetic makeup of organisms, eliminating the natural barriers that prevented transmission of genetic material between unrelated organisms. The ease of growing and manipulating bacteria and the numerous techniques available for introducing heterologous genes makes bacteria model organisms for genetic manipulation using recombinant DNA technology. Gram-negative and Gram-positive bacteria have been subjected to successful manipulation with recombinant DNA technology. Because of the well developed technology for transforming bacterial cells, the relative ease of genetically manipulating different bacteria, short reproduction times, and the comparatively small genomes, bacteria have been used as vehicles for synthetic biology applications, which aims to create novel artificial biological pathways, organisms or devices, or the redesign of existing natural biological systems. Moreover, bacteria exist with a wide range of functionalities, such as unique metabolic pathways (e.g., photo- and chemoautotrophism), magnetotactic properties (Blakemore, R., “Magnetotactic bacteria,” Science 24: 377-379, 1975), and extremophiles (e.g., thermophiles), which allows creation of recombinant bacteria with the properties present in the bacterial host cell.
Recombinant DNA techniques have also been used to manipulate the genetic makeup of eukaryotic cells, transiently or as a heritable property. For example, homologous and targeted recombination allows the generation of recombinant animals containing heterologous genes. Despite the advances in technology, manipulation of eukaryotic cells by recombinant DNA techniques has greater challenges as compared to manipulation of bacteria. Some eukaryotic cells targeted for recombinant DNA manipulation, e.g., mammalian cells, are slower to grow than bacterial cells, making selection of eukaryotic cells containing a heterologous nucleic acid more time consuming. Creation of eukaryotic cells containing longer lasting changes, including heritable changes, typically requires the use of homologous recombination, which despite the advances in technology, continue to have low efficiency rates. In addition, introduction of multiple, different heterologous nucleic acids is complicated by the higher complexity of eukaryotic cells (e.g., presence of organelles), greater degree of unpredictability in responses to multiple heterologous factors, and the technological disadvantages of selecting eukaryotic cells having multiple genetic/phenotypic changes. Thus, it is desirable to find alternative methods of engineering eukaryotic cells for introducing new functionalities into the cells, where the methods can be applied independently of or in combination with recombinant DNA technology for modifying eukaryotic cells.
SUMMARY
The present invention is related to host cells that have been altered or reprogrammed by communication and/or transfer of chemical information with artificial endosymbionts. In some embodiments, the artificial endosymbionts of the invention secrete to and/or transport from the host cell polypeptides, nucleic acids, lipids, carbohydrates, amino acids, or other factors. In some embodiments, the artificial endosymbiont secretes a protein into the host cell. In some embodiments, the secreted protein is a heterologous protein to the artificial endosymbiont. In some embodiments, the secreted protein from the artificial endosymbiont causes a phenotype in the host cell. In some embodiments, the artificial endosymbiont of the invention secretes a nucleic acid into the host cell. In some embodiments, the nucleic acid s a recombinant nucleic acid. In some embodiments, the nucleic acid secreted from the artificial endosymbiont causes a phenotype in the host cell.
The invention also relates to methods for changing a host cell by the introduction of an artificial endosymbiont that secretes to and/or transports from the host cell polypeptides, nucleic acids, lipids, carbohydrates, amino acids, or other factors. In some embodiments, the method introduces a protein into the host cell from the artificial endosymbiont. In some embodiments, the method introduces a nucleic acid into the host cell from the artificial endosymbiont. In some embodiments, the method produces a phenotype in the host cell resulting from the polypeptide and/or nucleic acid introduced from the artificial endosymbiont.
In some embodiments, the host cells and methods of the invention are used to make medically and industrially important recombinant peptides/proteins that will be useful for therapeutic, biopharmaceutical, agricultural, and industrial applications. In some embodiments, the artificial endosymbionts and methods of the invention are used to introduce into host cells phenotypes that require the introduction of multiple factors and/or multiple genes.
In some embodiments, the host cell is a mammalian cell. In some embodiments, the host cell is a human, mouse, rat, canine, primate, or rodent cell. In some embodiments, the host cell is a fibroblast cell, epithelial cell, keratinocyte, hepatocyte, adipocyte or endothelial cell. In some embodiments, the host cell is a stem cell, or pluripotent ES cell, or pluripotent iPS cell, a multipotent mesenchymal stem cell or multipotent hematopoietic stem cell. In some embodiments, the host cell is a progenitor cell, such as for example, a neural progenitor cell, an angioblast, an osteoblast, a chondroblast, a pancreatic progenitor cell, or an epidermal progenitor cell. In some embodiments, the host cell is a solid tumor cell or a hematopoietic cancer cell. In some embodiments, the host cell is from a carcinoma, sarcoma, leukemia, lymphoma, or glioma. In some embodiments, the host cell is obtained from a prostate cancer, breast cancer, lung cancer, colorectal cancer, pancreatic cancer, melanoma, glioblastoma, liver cancer, or the NCI 60 panel of cancer cell lines.



BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1A-1D depict BLAST results for a search with the amino acid sequence for Type V secretory pathway adhesin AidA (SEQ ID NO:1) from Magnetospirillum magneticum AMB-1. Exemplary sequences of homologous regions retrieved in the search, which included the search query Magnetospirillum magneticum AMB-1 adhesin AidA, are presented as SEQ ID NOS:1-103.
FIGS. 2A-2D depict BLAST results for a search with the amino acid sequence for protein accession no. YP_420640, annotated as RTX toxin from Magnetospirillum magneticum AMB-1 (SEQ ID NO:104). Exemplary sequences of homologous regions retrieved in the search, which included the search query Magnetospirillum magneticum AMB-1 RTX toxin YP_420640, are presented as SEQ ID NOS:104-122.
FIGS. 3A-3D depict BLAST results for a search with the amino acid sequence for protein accession no. YP_423419, annotated as RTX toxin from Magnetospirillum magneticum AMB-1 (SEQ ID NO:123). Exemplary sequences containing homologous regions retrieved in the search, which included the search query Magnetospirillum magneticum AMB-1 RTX toxin YP_423419, are presented as SEQ ID NOS:123-129.
FIGS. 4A-4D depict BLAST results for a search with the amino acid sequence for large exoprotein from Magnetospirillum magneticum AMB-1 (SEQ ID NO:130).
FIGS. 5A-5D depict BLAST results for a search with the amino acid sequence for Type V secretory pathway protein (accession no. YP_420638) (SEQ ID NO:131) from Magnetospirillum magneticum AMB-1.
FIGS. 6A-6D depict BLAST results for a search with the amino acid sequence for protein accession no. YP_422662 (SEQ ID NO:132), annotated as RTX toxin from Magnetospirillum magneticum AMB-1. Exemplary sequences of homologous regions retrieved in the search, which included the search query Magnetospirillum magneticum AMB-1 RTX toxin YP_422662, are presented as SEQ ID NOS:132-140.
FIG. 7 depicts BLAST results for a search with the 949 C-terminal amino acids of YP 422785 (SEQ ID NO: 141) from Magnetospirillum magneticum AMB-1. Exemplary sequences of homologous regions retrieved in the search, which included YP 422785, are presented as SEQ ID NOS:141-253.
FIGS. 8A-8D depict BLAST results for a search with the amino acid sequence for ABC-type protease/lipase transport system, ATPase and permease components (SEQ ID NO:254) from Magnetospirillum magneticum AMB-1. Exemplary sequences of homologous regions retrieved in the search, which included the search query Magnetospirillum magneticum AMB-1ATPase and permease, are presented as SEQ ID NOS:254-268.
FIGS. 9A-9C depict BLAST results for a search with the amino acid sequence for thermostable lipase TliA (SEQ ID NO:269) from Pseudomonas flourescens. Exemplary sequences of homologous regions retrieved in the search are presented as SEQ ID NOS:270-286.
FIG. 10 shows levels of green fluorescence in extracellular supernatants of AC16 cells (M. magneticum AMB-1 containing GFP fused to the C-terminal transport sequence of NCBI Accession No. YP_422785) as compared to that of the M. magneticum AMB-1 negative control (denoted as AMB-1 Neg Ctrl) (see Example 4).
FIG. 11 shows levels of green fluorescent protein fluorescence in supernatants of cultures of AC16 cells as compared to fluorescence levels of suspensions of AC16 cells. Also shown are fluorescence levels of supernatant of M. magneticum AMB-1 Neg Ctrl cells as compared to M. magneticum AMB-1 Neg Ctrl cells in suspension.
FIG. 12 shows fluorescence microscopy of AMB-1 labeled MDA-MB231 cells (40× images). MDA-MB231 cells were labeled with AMB-1, where the AMB-1 contained (A) only GFP plasmid or (B) GFP-fused to C-terminal 200 amino acids of YP_422785 (i.e., AC16), and dually stained for GFP and AMB-1 one day post-labeling with bacteria and examined by fluorescence microscopy (see Example 4 for details). Both panels are merged images of staining of GFP (red), AMB-1 (green), and DAPI (blue).
FIG. 13 shows fluorescence microscopy of AMB-1 labeled MDA-MB231 cells (single channel and composite images) (40× images). MDA-MB231 cells were labeled with AMB-1 containing GFP plasmid only, and dually stained one day post-labeling and examined by fluorescence microscopy. Top left panel (A) represents AMB-1 staining (green channel), (B) top right panel GFP staining (red channel), (C) bottom left panel DAPI staining (blue channel), and (D) merged images of AMB-1 (green channel), GFP (red channel), and DAPI (blue channel) staining.
FIG. 14 shows fluorescence microscopy of AMB-1 labeled MDA-MB231 cells (single channel and composite images) (40× images). MDA-MB231 cells were labeled with AMB-1 containing GFP-fused to C-terminal 200 amino acids of YP_422785 (AC16), and dually stained one day post-labeling and examined by fluorescence microscopy. Top left panel (A) represents AMB-1 staining (green channel); top right panel (B) represents GFP staining (red channel); bottom left panel (C) represents DAPI staining (blue channel); and bottom right panel (D) represents merged images of AMB-1 (green channel), GFP (red channel), and DAPI (blue channel) staining.



DETAILED DESCRIPTION
The present invention is directed to host cells that contain an artificial endosymbiont, wherein the artificial endosymbiont secretes into and/or transports from the host cell a polypeptide, nucleic acid, or other factor. In some embodiments, the factor, e.g., a protein or nucleic acid, is secreted into the host cell and produces a phenotype in the host cell, particularly a phenotype not present prior to the introduction of the artificial endosymbiont into the host cell. In some embodiments, the artificial endosymbiont secretes into and/or transports from the host cell two or more factors (i.e., multiple factors). In some embodiments, secretion into the host cell can use the endogenous secretion machinery and secretion signals (e.g., sequences) of the artificial endosymbiont, or the artificial endosymbiont engineered to contain the secretion systems for transport of the factor into the host cell.
Before various embodiments of the present invention are further described, it is to be understood that this disclosure is not limited to the particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purposes of describing particular embodiments only, and is not intended to be limiting.
It is also to be noted that as used in the present disclosure and in the appended claims, the singular terms “a”, “an”, and “the” include plural referents unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” (and vice versa) unless the context clearly indicates otherwise. In addition, the use of “or” means “and/or” unless stated otherwise.
In addition, the words “comprise,” “comprises,” “comprising,” “include,” “includes,” and “including” are interchangeable and not intended to be limiting. Where descriptions of various embodiments use the term “comprising,” those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language “consisting essentially of” or “consisting of.”
Numerical limitations given with respect to concentrations or levels of a substance are intended to be approximate. Thus, where a concentration is indicated to be at least (for example) 10 μg, it is intended that the concentration be understood to be at least approximately or about 10 μg.
The section headings used herein are for organizational purposes only and not to be construed as limiting the subject matter described.
Definitions
As used herein, the term “artificial endosymbiont” refers to a single-celled organism that is or has been introduced into a host cell through human intervention. The single-celled organism secretes to and/or transports from the host cell polypeptide(s), nucleic acid(s), lipid(s), carbohydrate(s), amino acid(s), or other factor(s). And this communication between the single cell organism and the host cell results in a phenotype for the host cell and/or artificial endosymbiont.
As used herein, the term “cellular life cycle” refers to series of events involving the growth, replication, and division of a eukaryotic cell. It is generally divided into five stages, known as G0, in which the cell is quiescent, G1 and G2, in which the cell increases in size, S, in which the cell duplicates its DNA, and M, in which the cell undergoes mitosis and divides.
As used herein, the term “daughter cell” refers to cells that are formed by the division of a cell.
As used herein, the term “essential molecule” refers to a molecule needed by a cell for growth or survival.
As used herein, the term “genetically modified” refers to altering the DNA of a cell so that a desired property or characteristic of the cell is changed.
As used herein, the term “magnetosome” refers to particles of magnetite (i.e., Fe3O4) or greigite (Fe3S4) enclosed by a sheath or membrane, either as individual particles or in chains of particles.
As used herein, the term “magnetotactic bacteria” or “MTB” refers to bacteria which are able to orient in a magnetic field.
As used herein, the term “mammal” refers to warm-blooded vertebrate animals all of which are characterized by hair on the skin and, in the female, milk producing mammary glands.
As used herein, the term “phenotype” refers to the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
As used herein, the term “secrete” refers to the passing of molecules or signals from one side of a membrane to the other side.
As used herein, the term “heterologous” when used in reference to a nucleic acid or polypeptide refers to a nucleic acid or polypeptide not normally present in nature. Accordingly, a heterologous nucleic acid or polypeptide in reference to a host cell, such as an artificial endosymbiont, refers to a nucleic acid or polypeptide not naturally present in the given host cell. For example, a nucleic acid molecule containing a non-host nucleic acid encoding a polypeptide operably linked to a host nucleic acid comprising a promoter is considered to be a heterologous nucleic acid molecule. Conversely, a heterologous nucleic acid molecule can comprise an endogenous structural gene operably linked with a non-host (exogenous) promoter. Similarly, a peptide or polypeptide encoded by a non-host nucleic acid molecule, or an endogenous polypeptide fused to a non-host polypeptide is a heterologous peptide or polypeptide.
Unless specific definitions are provided, all other technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Definitions of common terms in molecular biology may be found in, for example, Benjamin Lewin, Genes V, Oxford University Press (1994); The Encyclopedia of Molecular Biology, John Kendrew, ed., Blackwell Science Ltd. (1994); and Molecular Biology and Biotechnology: a Comprehensive Desk Reference, Robert A. Meyers, ed., VCH Publishers, Inc. (1995).
Artificial Endosymbionts
In one aspect, the artificial endosymbionts of the present invention include single-celled organisms, e.g., bacteria, that are capable of surviving in a eukaryotic cell, wherein the artificial endosymbiont secretes into and/or transports from the host cell a polypeptide(s), nucleic acid(s), or other factor(s). In some embodiments, the polypeptide and/or nucleic acid are recombinant or heterologous to the artificial endosymbiont. In some embodiments, the artificial endosymbiont introduces a phenotype into the host cell through the secretion and/or transport between the host cell and the artificial endosymbiont. In some embodiments, this phenotype introduced into the host cell by the artificial endosymbiont is maintained in daughter cells of the host cell. In some embodiments, the host cell maintains the functionality for at least 1 day, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 days. In some embodiments, the artificial endosymbiont can stably maintain the phenotype in host daughter cells through at least 3 cell divisions, or at least 4 cell divisions, or at least 5 cell divisions, or at least 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more cell divisions. In some embodiments, the artificial endosymbiont can stably maintain phenotype in the host daughter cells through 3-5 divisions, or 5-10 divisions, or 10-15 divisions, or 15-20 divisions.
In some embodiments, the artificial endosymbionts are Proteobacteria, particularly α-Proteobacteria. In the current taxonomic scheme based on 16S rRNA, α-proteobacteria are recognized as a Class within the phylum Proteobacteria, and are subdivided into 7 main subgroups or orders (Caulobacterales, Rhizobiales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales and Parvularculales) (Gupta, R. S., “Phylogenomics and signature proteins for the alpha Proteobacteria and its main groups,” BMC Microbiol. 7:106, 2007; incorporated herein by reference).
A large number of α-proteobacterial genomes that cover all of the main groups within α-proteobacteria have been sequenced, providing information that can be used to identify unique sets of genes or proteins that are distinctive characteristics of various higher taxonomic groups (e.g., families, orders, etc.) within α-proteobacteria. (Gupta, supra). Analyses of these sequenced genomes show that many species of α-proteobacteria contain transport systems useful in the present invention. FIGS. 1-9 show BLAST homology searches performed at NCBI protein blast website (blast.ncbi.nlm.nih.gov/Blast.cgi), and these searches show that many α-proteobacteria species have protein coding sequences homologous to proteins of Type 1 and 5 secretion systems. Thus, in some embodiments, the artificial endosymbionts comprise α-proteobacteria.
In some embodiments, an exemplary α-proteobacteria is magnetotactic bacteria (MTB). MTB are a diverse group of bacteria that belong to different subgroups of the Proteobacteria and Nitrospirae phylum, and are mostly represented within the α-proteobacteria. MTB have a Gram-negative cell wall structure (e.g., inner membrane, periplasm, and outer membrane). They inhabit water bodies or sediments with vertical chemical concentration gradient, predominantly at the oxic-anoxic interface, and thus in some instances categorized as microaerophiles, anaerobic, facultative aerobic or some combination of the three. All MTB are chemoorganoheterotrophic although some marine strains can also grow chemolithoautotrophically (Bazylinski et al., “Chemolithoautotrophy in the marine, magnetotactic bacterial strains MV-1 and MV-2,” Arch Microbiol. 182(5):373-87, 2004; Williams et al., “Evidence for autotrophy via the reverse tricarboxylic acid cycle in the marine magnetotactic coccus strain MC-1,” Appl Environ Microbiol. 72(2):1322-9, 2006). All MTB contain magnetosomes, which are intracellular structures comprising magnetic iron crystals enveloped by a phospholipid bilayer membrane (Gorby et al., “Characterization of the bacterial magnetosome membrane,” J Bacteriol. 170(2):834-41, 1988). In some embodiments, the transport pathways of MTB deliver endogenous and exogenous proteins and/or nucleic acids to the host cell.
A large number of MTB species are known to those of ordinary skill in the art since their initial discovery (Blakemore, R., “Magnetotactic bacteria,” Science 24:377-79, 1975; Faivre, D. and Schüler, D., “Magnetotactic bacteria and magnetosomes,” Chem Rev. 108:4875-4898, 2008; publications incorporated herein by reference). MTB have been identified in different subgroups of the Proteobacteria and the Nitrospira phylum, with most of the phylotypes grouping in α-Proteobacteria. Currently, culturable MTB strains assigned as α-Proteobacteria by 16S rRNA sequence similarity include the strain originally isolated by Blakemore in 1975, Magnetospirillum magnetotactium (formerly Aquasprillium magnetotactium), M. gryphiswaldense, M. magneticum strain AMB-1, M. polymorphum, Magnetospirillum sp. MSM-4 and MSM-6, Magnetococcus marinus, marine vibrio strains MV-1 and MV-2, a marine spirillum strain MMS-1 and Magnetococcus sp. strain MC-1, as well as others. In some embodiments, all such MTB can be used in the present invention.
Other bacteria useful as artificial endosymbionts include, for example, Anabaena, Nostoc, Diazotroph, Cyanobacteria, Trichodesmium, Beijerinckia, Clostridium, Green sulfur bacteria, Azotobacteraceae, Rhizobia, Frankia, flavobacteria, Methanosarcinales, aerobic halophilic Archaea of the order Halobacteriales, the fermentative anaerobes of the order Halanaerobiales (low G+C brand of the Firmicutes), the red aerobic Salinibacter (Bacteroidetes branch), Marinobacter, Halomonas, Dermacoccus, Kocuria, Micromonospora, Streptomyces, Williamsia, Tskamurella, Alteromonas, Colwellia, Glaciecola, Pseudoalteromonas, Shewanella, Polaribacter, Pseudomonas, Psychrobacter, Athrobacter, Frigoribacterium, Subtercola, Microbacterium, Rhodoccu, Bacillus, Bacteroides, Propionibacterium, Fusobacterium, Klebsiella, lecithinase-positive Clostridia, Veillonella, Fusobacteria, Chromatiaceae, Chlorobiceae, Rhodospirillaceae, thiobacilli, nitrosomonas, nitrobacter, methanogens, acetogens, sulfate reducers, and lactic acid bacteria.
The genomes of a number of artificial endosymbionts have been or are being sequenced: M. frigidum, M. burtonii, C. symbiosum, C. psychrerythraea, P. haloplanktis, Halorubrum lacusprofundi, Vibrio salmonicida, Photobacterium profundum, S. violacea, S. frigidimarina, Psychrobacter sp. 273-4, S. benthica, Psychromonas sp. CNPT3, Moritella sp., Desulfotalea Psychrophila, Exiguobacterium 255-15, Flavobacterium psychrophilum, Psychroflexus torquis, Polaribacter filamentous, P. irgensii, Renibacterium salmoninarum, Leifsonia-related PHSC20-c1, Acidithiobacillus ferrooxidans, Thermoplasma acidophilum, Picrophilus torridus, Sulfolobus tokodaii, and Ferroplasma acidarmanus. 
Secretion Systems of Artificial Endosymbionts
In the present invention, secretion of protein(s), nucleic acid(s), other molecule(s) and other factor(s) from the artificial endosymbiont, particularly α-proteobacteria and more particularly magnetotactic bacteria, can make use of the endogenous secretion systems of the artificial endosymbiont. In some embodiments, the artificial endosymbiont can be engineered with heterologous secretion systems, or portions thereof, for directed secretion of these target molecules. In some embodiments, these transport systems of the invention are used to transport medically and industrially important genes, recombinant peptides/proteins, and/or other factors that will be useful for therapeutic, biopharmaceutical, agricultural, and industrial applications. However, although various secretion systems are known in the art and described in the present disclosure, it is to be understood that practice of the present invention does not require knowledge or understanding of a specific secretion system. Generally, the signals or sequences that cause secretion of polypeptides or other factors are known for many single celled organisms; they can also be found on known secreted proteins or nucleic acids, or identified based on similarities to sequences found on secreted proteins or nucleic acids. These secretion signals can then be used, particularly as fusions, to direct a target molecule for secretion in the artificial endosymbiont into the host cell without prior knowledge of the specific transport system that directs secretion using the particular secretion signal.
Various secretion systems can be used in the artificial endosymbionts of the disclosure, e.g., a magnetotactic bacteria. For example, the α-proteobacteria have transport pathways that include ABC transporter-based pathways (including the type I secretion system, T1SS), type II secretion systems (T2SS), type III secretion systems (T3SS), type IV secretion systems (T4SS), type V secretion systems (T5SS), type VI secretion systems (T6SS), type VII secretion systems (T7SS), and other transport systems that are known in the art. In some embodiments, these transport systems of α-proteobacteria are used to transport proteins, nucleic acids, and other factors from the artificial endosymbiont into the host cell. In Gram-negative bacteria, secreted proteins are exported across the inner and outer membrane in a single step via the T1SS, T3SS, T4SS, and T6SS pathways. Proteins are exported into the periplasmic space across inner membrane via Sec or two-arginine (Tat) pathways. Proteins are transported across the outer membrane from the periplasmic space by T2SS, T5SS or less commonly by T1SS or T4SS.
T1SS consists of three proteins; an inner membrane protein with a cytoplasmic ATPase domain operating as an ATP-binding cassette (ABC) transporter (Escherichia coli HlyB), a periplasmic adaptor (also known as membrane fusion protein, MFP; E. coli HlyD), and an outer membrane channel protein of the TolC family (E. coli TolC) (reviewed in Delepelaire, P., “Type I secretion in gram-negative bacteria,” Biochem Biophy Acta 1694:149-61, 2004). These proteins form a pore through the periplasm via which an unfolded protein may be translocated. T1SS protein substrates typically contain carboxy-terminal, glycine- and aspartate-rich repeats known as repeat-in-toxin (RTX) (Linhartova et al., “RTX proteins: a highly diverse family secreted by a common mechanism,” FEMS Microbiol Rev. 34:1076-1112, 2010; incorporated herein by reference) and are often located close to ABC and MFP genes. Due to its simplicity, T1SS has been used to transport heterologous proteins. Several studies have shown the utility of T1SS to transport exogenous proteins to the extracellular medium (see, e.g., Delepelaire, P., supra; Reed, B and Chen, R., “Biotechnological applications of bacterial protein secretion: from therapeutics to biofuel production,” Res Microbiol. 164:675-682, 2013; all of which are incorporated herein by reference in their entirety). Low et al. found that cyclodextrin glucanotransferase secretion could be improved by overexpression of the E. coli α-haemolysin transporter (Low, K. O. et al., “An effective extracellular protein secretion by an ABC transporter system in Escherichia coli: statistical modeling and optimization of cyclodextrin glucanotransferase secretory production,” J Ind Microbiol Biotechnol. 38: 1587-97, 2011; incorporated herein by reference in its entirety). Su and coworkers also used E. coli α-haemolysin secretion systems to secrete protein. By overexpressing HlyBD, two strain-specific components of T1SS, they showed that the recombinant T1SS secreted a high level (1.5 g per liter) of protein from an E. coli (Su, L. et al., “Extracellular overexpression of recombinant Thermobifida fusca cutinase by alpha-hemolysin secretion system in E. coli BL21 (DE3),”Microb Cell Fact. 11:8, 2012; incorporated herein by reference in its entirety). The E. coli hemolysin transporter is also known to secrete other heterologous T1SS substrates expressed in E. coli, including exotoxins Cya of Bordatella. pertussis (Sebo, P., and Ladant, D., “Repeat sequences in the B. pertussis adenylate cyclase toxin can be recognized as alternative carboxy-proximal secretion signals by the E. coli alpha-haemolysin translocator,” Mol Microbiol. 9: 999-1009, 1993), LtkA of Aggregatibacter actinomycetemcomitans (Lally, E. T. et al., “Analysis of the Actinobacillus actinomycetemcomitans leukotoxin gene, Delineation of unique features and comparison to homologous toxins,” J Biol Chem. 264:15451-456, 1989), PaxA of Pasteurella aerogenes (Kuhnert, P. et al., “Characterization of PaxA and its operon: a cohemolytic RTXtoxin determined from pathogenic Pasteurella aerogenes,” Infect. Immun. 68:6-12, 2000), and FrpA of Neisseria meningitidis (Thompson, S. A. and Sparling, P. E., “The RTX cytotoxin-related FrpA protein of Neisseria miningitidis is secreted extracellularly by meningococci and by HlyBD+Escherichia coli.” Infect Immun. 61:2906-11, 1993; all of which are incorporated herein by reference in their entirety). The assembly of the T1SS complex (best exemplified by E. coli hemolysin (Hly) secretion system) is nucleotide-independent, and the translocation of HlyA (the T1SS substrate) requires ATP hydrolysis catalyzed by HlyB (Thanabalu, T. et al., “Substrate-induced assembly of a contiguous channel for the protein export from E. coli: reversible bridging of an inner-membrane translocase to an outer membrane exit pore,” EMBO J. 17:6487-96, 1998; incorporated by reference in its entirety). HlyA is member of the RTX (repeats in toxin) protein family and contains glycine-rich peptide repeats in the C-terminal domain, which have the consensus sequence GGXGXD (X represents any amino acid) (SEQ ID NO:287) and are important for the binding of Ca2+ ions. This triggers folding of HlyA in the extracellular medium, which in turn generates the biologically active form of the toxin. The T1SS substrates contain a translocation signal at the C-terminus (last 27 to 218-amino acid fragment of HlyA, minimal secretion signal is located within the last  ̃60 C-terminal amino acids and is both necessary and sufficient to direct secretion) (Kenny, B. et al., “Analysis of the haemolysin transport process through the secretion from E. coli of PCM, CAT or beta-galactosidase fused to the C-terminal signal domain,” Mol Microbiol. 5:2557-68, 1991; incorporated herein by reference in its entirety). Proteins targeted to the translocator carry an uncleaved, poorly conserved secretion signal at the extreme C-terminus (absolutely required for secretion) that binds to the nucleotide binding domain of ABC-ATPase (E. coli HlyB) in a reaction reversible by ATP that mimic initial movement of HlyA into the translocation channel and rapid transport of HlyA to the extracellular medium (Holland B. et al., “Type 1 protein secretion in bacteria, the ABC-transporter dependent pathway (Review),” Mol Membr Biol. 22:29-39, 2005; incorporated herein by reference in its entirety).
T1SS from Pseudomonas fluorescens is also known and has been used to secrete recombinant proteins. Park et al. found a 105 amino acid polypeptide as the minimal region for recognition and transport by the lipase ABC transporter. A fusion of a target protein to this minimal region allowed secretion of recombinant protein (Park, Y. et al., “Identification of the minimal region in lipase ABC transporter recognition domain of Pseudomonas fluorescens for secretion and fluorescence of green fluorescent protein,” Microb. Cell. Fact. 11:60, 2012; incorporated herein by reference in its entirety). The versatility of T1SS for protein secretion is seen in its wide array of transport substrates, which vary from small proteins like the hemophore HasA (19 kDa) to huge surface layer proteins up to 900 kDa in size (Linhartova et al., “RTX proteins: a highly diverse family secreted by a common mechanism,” FEMS Microbiol Rev. 34:1076-1112, 2010; Satchell, K. J., “Structure and function of MARTX toxins and other large repetitive RTX proteins,” Annu Rev Microbiol. 65:71-90, 2011; all of which are incorporated herein by reference in their entirety). Other proteins secreted by T1SS include, for example adenylate cyclases, lipases and proteases.
Another T1SS system that can be used in the invention is RaxABC from Xanthomonas oryzae pv. oryzae. Phylogenetic analysis identifies RaxB as an ABC transporter (da Silva, F. G. et al., “Bacterial genes involved in type I secretion and sulfation are required to elicit the rice Xa21-mediated innate immune response,” Mol Plant Microbe Interact. 17:593-601, 2004; incorporated herein by reference in its entirety), equivalent to HlyB from E. coli. The RaxABC transport system is used to secrete AvrXa21 molecules (small sulfated polypeptides), metalloproteases, adhesion factors and glycanases (Delepelaire, P., “Type I secretion in gram-negative bacteria,” Biochim Biophys Acta 1694: 149-161, 2004; Reddy, J. D. et al., “TolC is required for pathogenicity of Xylella fastidioa in Vitis vinifera grape-vines,” Mol Plant Microbe Interact. 20:403-410, 2007; all of which are incorporated herein by reference in their entirety).
Autotransporter systems, a subset of T5SS, provide potentially the simplest mechanism for extracellular secretion of recombinant proteins. An autotransporter consists of an N-terminal Sec-dependent signal sequence, a passenger domain and a C-terminal beta-motif. The translocation is a two-step process. The target protein is transported into the periplasm using Sec-dependent transport whereupon the beta-motif forms a transmembrane pore through which the passenger domain is secreted out of the periplasm (Dautin, N. and Barnstein, H. D., “Protein secretion in gram-negative bacteria via the autotransporter pathway,” Annu Rev Microbiol. 61:89-112, 2007; Thanassi, D. G., et al., “Protein secretion in the absence of ATP: the autotransporter, two-partner secretion and chaperone/usher pathways of gram-negative bacteria (Review),” Mol Membr Biol. 22:63-72, 2005; all of which are incorporated herein by reference in their entirety). The beta-motif can be cleaved, allowing translocation of the target protein out of the cell (Leyton, D. L. et al., “From self sufficiency to dependence: mechanism and factors important for autotransporter biogenesis,” Nat Rev Microbiol. 10:213-25, 2012; incorporated herein by reference in its entirety).
For transport in the T5 SS system, the target protein is fused with the N-terminal signal sequence and the C-terminal signal, beta-domain that mediate translocation of a recombinant protein through the inner and outer membranes, respectively. This chimera gene has the N-terminal signal sequence fused in frame to the N-terminal end of the target gene, and a second, in frame fusion to DNA encoding the beta-domain sequence at the C-terminal end of the target gene. In some embodiments, the passenger domain may be replaced in the fusion protein. For example, Jong et al. defined passenger domains of E. coli autotransporter hemoglobin-binding protease (Hbp) that could be replaced in a fusion protein to facilitate secretion, along with an intact beta-domain (Jong, W. S. et al., “A structurally informed autotransporter platform for efficient heterologous protein secretion and display,”Microb Cell Fact. 11:85, 2012; incorporated herein by reference in its entirety). As such, the Hbp (NCBI Accession no. O88093, 1377 amino acids) passenger domains that can be replaced by heterologous proteins include the following: (1) 53-308; (2) 533-608; (3) 657-697; (4) 735-766; (5) 898-922 amino acids:







(SEQ ID NO: 288)


MNRIYSLRYSAVARGFIAVSEFARKCVHKSVRRLCFPVLLLIPVLFSAG


 


SLAGTVNNELGYQLFRDFAENKGMFRPGATNIA'YNKQGEFVGTLDKAA


 


MPDFSAVDSEIGVATLINPQYIASVKHNGGYINVSFGDGENRYNIVDRN


 


NAPSLDFHAPRLDKLVTEVAPTAVTAQGAVAGAYLDKERYPVFYRLGSG


 


TQYIKDSNGQLTKMGGAYSWLTGGTVGSLSSYQNGEMISTSSGLVFDYK


 


LNGAMPIYGEAGDSGSPLFAFDTVQNKWVLVGVLTAGNGAGGRGNNWAV


 


IPLDFIGQKFNEDNDAPVTFRTSEGGALEWSFNSSTGAGALTQGTTTYA


 


MHGQQGNDLNAGKNLIFQGQNGQINLKDSVSQGAGSLTFRDNYTVTTSN


 


GSTWTGAGIVVDNGVSVNWQVNGVKGDNLHKIGEGTLTVQGTGINEGGL


 


KVGDGKVVLNQQADNKGQVQAFSSVNIASGRPTVVLTDERQVNPDTVSW


 


GYRGGTLDVNGNSLTFHQLKAADYGAVLANNVDKRATITLDYALRADKV


 


ALNGWSESGKGTAGNLYKYNNPYTNTTDYFILKQSTYGYFPTDQSSNAT


 


WEFVGHSQGDAQKLVADRFNTAGYLFHGQLKGNLNVDNRLPEGVTGALV


 


MDGAADISGTFTQENGRLTLQGHPVIHAYNTQSVADKLAASGDHSVLTQ


 


PTSFSQEDWENRSFTFDRLSLKNTDFGLGRNATLNTTIQADNSSVTLGD


 


SRVFIDKNDGQGTAFTLEEGTSVATKDADKSVFNGTVNLDNQSVLNIND


 


IFNGGIQANNSTVNISSDSAVLGNSTLTSTALNLNKGANALASQSFVSD


 


GPVNISDATLSLNSRPDEVSHTLLPVYDYAGSWNLKGDDARLNVGPYSM


 


LSGNINVQDKGTVTLGGEGELSPDLTLQNQMLYSLFNGYRNIWSGSLNA


 


PDATVSMTDTQWSMNGNSTAGNMKLNRTIVGFNGGTSPFTTLITDNLDA


 


VQSAFVMRTDLNKADKLVINKSATGHDNSIWVNFLKKPSNKDTLDIPLV


 


SAPEATADNLFRASTRVVGFSDVTPILSVRKEDGKKEWVLDGYQVARND


 


GQGKAAATFMHISYNNFITEVNNLNKRMGDLRDINGEAGTWVRLLNGSG


 


SADGGFTDHYTLLQMGADRKHELGSMDLFTGVMATYTDTDASADLYSGK


 


TKSWGGGFYASGLFRSGAYFDVIAKYIHNENKYDLNFAGAGKQNFRSHS


 


LYAGAEVGYRYHLTDTTFVEPQAELVWGRLQGQTFNWNDSGMDVSMRRN


 


SVNPLVGRTGVVSGKTFSGKDWSLTARAGLHYEFDLTDSADVHLKDAAG


 


EHQINGRKDSRMLYGVGLNARFGDNTRLGLEVERSAFGKYNTDDAINAN


 


IRYSF






Many E. coli autotransporters can also be used in the present invention. Ko et al. used the YfaL autotransporter (NCBI accession no. P45508) to secrete proteins ranging from 25.3 to 143 kDa from E. coli (Ko, H. J., et al., “Functional cell surface display and controlled secretion of diverse agarolytic enzymes by Escherichia coli with a novel ligation-independent cloning vector based on the autotransporter YfaL,” Appl Environ Microbiol. 78:3051-58, 2012; incorporated herein by reference in its entirety). The YfaL autotransporter comprises the following sequence:







(SEQ ID NO: 289)


MRIIFLRKEYLSLLPSMIASLFSANGVAAVTDSCQGYDVKASCQASRQS


 


LSGITQDWSIADGQWLVFSDMTNNASGGAVFLQQGAEFSLLPENETGMT


 


LFANNTVTGEYNNGGAIFAKENSTLNLTDVIFSGNVAGGYGGAIYSSGI


 


NDTGAVDLRVTNAMFRNNIANDGKGGAIYTINNDVYLSDVIFDNNQAYT


 


STSYSDGDGGAIDVTDNNSDSKHPSGYTIVNNTAFTNNTAEGYGGAIYT


 


NSVTAPYLIDISVDDSYSQNGGVLVDENNSAAGYGDGPSSAAGGFMYLG


 


LSEVTFDIADGKTLVIGNTENDGAVDSIAGTGLITKTGSGDLVLNADNN


 


DFTGEMQIENGEVTLGRSNSLMNVGDTHCQDDPQDCYGLTIGSIDQYQN


 


QAELNVGSTQQTFVHALTGFQNGTLNIDAGGNVTVNQGSFAGIIEGAGQ


 


LTIAQNGSYVLAGAQSMALTGDIVVDDGAVLSLEGDAADLTALQDDPQS


 


IVLNGGVLDLSDFSTWQSGTSYNDGLEVSGSSGTVIGSQDVVDLAGGDN


 


LHIGGDGKDGVYVVVDASDGQVSLANNNSYLGTTQIASGTLMVSDNSQL


 


GDTHYNRQVIFTDKQQESVMEITSDVDTRSDAAGHGRDIEMRADGEVAV


 


DAGVDTQWGALMADSSGQHQDEGSTLIKTGAGTLELTASGTTQSAVRVE


 


EGTLKGDVADILPYASSLWVGDGATFVTGADQDIQSIDAISSGTIDISD


 


GTVLRLTGQDTSVALNASLFNGDGILVNATDGVILTGELNINLETDSLT


 


YLSNVTVNGNLTNTSGAVSLQNGVAGDTLTVNGDYTGGGTLLLDSELNG


 


DDSVSDQLVMNGNTAGNITVVVNSITGIGEPTSTGIKVVDFAADPTQFQ


 


NNAQFSLAGSGYVNMGAYDYTLVEDNNDWYLRSQEVTPPSPPDPDPTPD


 


PDPTPDPDPTPDPEPTPAYQPVLNAKVGGYLNNLRAANQAFMMERRDHA


 


GGDGQTLNLRVIGGDYHYTAAGQLAQHEDTSTVQLSGDLFSGRWGTDGE


 


WMLGIVGGYSDNQGDSRSNMTGTRADNQNHGYAVGLTSSWFQHGNQKQG


 


AWLDSWLQYAWFSNDVSEQEDGTDHYHSSGIIASLEAGYQWLPGRGVVI


 


EPQAQVIYQGVQQDDFTAANRARVSQSQGDDIQTRLGLHSEWRTAVHVI


 


PTLDLNYYHDPHSTEIEEDGSTISDDAVKQRGEIKVGVTGNISQRVSLR


 


GSVAWQKGSDDFAQTAGFLSMTVKW






In some embodiments, a protease (e.g., a tobacco etch virus protease) is used to cleave the C-terminus of the fusion proteins to remove the beta-domain and autotransporter, resulting in secretion from the cell. Sevastsyanovich et al. utilized the E. coli serine protease Pet to cleave fusion proteins and provide for complete secretion of a range of proteins varying in sizes and structures, including multi-component proteins (Sevastsyanovich, Y. R. et al., “A generalized module for the selective extracellular accumulation of recombinant proteins,” Microb Cell Fact. 11:69, 2012; incorporated herein by reference in its entirety). Pet is one of the serine protease autotransporters of the Enterobacteriaceae (SPATEs) that releases passenger domain from the beta-domain.
An application of an autotransporter for consolidated bioprocessing uses an E. coli autotransporter Antigen 43 (Ag43) engineered to secrete a target protein. This autotransporter system is unique in that the passenger domain Ag43alpha is self-cleaved, yet the secreted domain is non-covalently attached to the beta-domain, forming an integral outer-membrane protein. In order to secrete the recombinant protein, the segment of Ag43alpha containing the cleavage mechanism was fused to a target sequence. When engineered into an E. coli strain, the self-cleaving autotransporter secreted target protein out of the cell (Wargacki, A. J. et al., “An engineered microbial platform for direct biofuel production from brown macroalgae,” Science 335:308-13, 2012; incorporated herein by reference in its entirety).
A very large number of proteins are secreted via the T5SS, more even than the T2SS (Jacob-Dubuisson, F. et al., “Protein secretion through autotransporter and two-partner pathway,” Biochem Biophy Acta 1694:235-57, 2004; Dautin, N. and Bernstein, H. D., “Protein secretion in the gram-negative bacteria via autotransporter pathway,” Ann Rev Microbiol. 61:89-112, 2007). Most of the T5SS secreted proteins characterized to date are virulence factors. Proteins secreted via the T5SS include adhesins such as AIDA-I and Ag43 of E. coli, Hia of Haemophilus influenzae, YadA of Yersinia enteroliticola, and Pm of Bordetella pertussis; toxins such as VacA of Helicobacter pylori; proteases such as IgA proteases of Neisseria gonorrheae and Neisseria meningitides, SepA of Shigella flexneri and PrtS of Serratia marcescens; and S-layer proteins such as rOmpB of Rickettsia sp. and Hsr of Helicobacter pylori. T5bSS (TPS) secreted proteins include adhesins such as HecA/HecB of the plant pathogen Dickeya dadantii (Erwinia chrysanthemii) and cytolysins such as Sh1A/Sh1B of Serratia marcescens, HpmA/HpmB of Proteus mirabilis and EthA/EthB of Edwardsiella tarda. 
The type IV secretion system (T4SS) is a versatile, multi-component secretion system used by both gram-negative and gram-positive bacteria to secrete proteins, DNA, and protein-DNA complexes into a wide range of targeted eukaryotic and bacterial cells (Fronzes, R. et al., “The Structural Biology of Type IV Secretion Systems,” Nat Rev Microbiol 7(10):703-14, 2009; Backert, S. and T. F. Meyer. “Type IV Secretion Systems and Their Effectors in Bacterial Pathogenesis,” Curr Opin Microbiol 9(2): 207-17, 2006; all of which are hereby incorporated by reference in their entirety) and can be divided into three groups (Fronzes, R. et al., supra; incorporated herein by reference in its entirety). Group 1 T4SSs mediate the conjugative transfer of plasmid DNA or transposons into a wide range of bacterial species. For example, E. coli and Agrobacterium tumefaciens can deliver DNA substrates into fungal, plant of human cells (Grohmann, E. et al., “Conjugative Plasmid Transfer in Gram-Positive Bacteria,” Microbiol Mol Biol Rev 67(2): 277-301, 2003; Lawley, T. D. et al., “F Factor Conjugation Is a True Type Iv Secretion System,” FEMS Microbiol Lett. 224(1):1-15, 2003; Trieu-Cuot, P. et al., “In Vivo Transfer of Genetic Information between Gram-Positive and Gram-Negative Bacteria,” EMBO J. 4(13A):3583-7, 1985; all of which are hereby incorporated by reference in their entirety). T4SSs in group 2, such as those found in Helicobacter pylori and Neisseria gonorrhea, mediate the uptake and release of DNA into the extracellular environment (Smeets, L. C. and J. G. Kusters, “Natural Transformation in Helicobacter Pylori: DNA Transport in an Unexpected Way,” Trends Microbiol. 10(4) 159-62, 2002 (discussion 162); Hamilton, H. L. and J. P. Dillard, “Natural Transformation of Neisseria Gonorrhoeae: From DNA Donation to Homologous Recombination,” Mol Microbiol. 59(2): 376-85, 2006; all of which are hereby incorporated by reference in their entirety). Group 3 T4SSs deliver effector molecules into eukaryotic cells during infection. H. pylori, Brucella suis and Legionella pneumophila are examples of bacteria that use their T4SSs to inject virulence proteins into mammalian host cells (Backert, S. and Meyer, T. F., “Type IV Secretion Systems and Their Effectors in Bacterial Pathogenesis,” Curr Opin Microbiol. 9(2): 207-17, 2006; Corbel, M. J., “Brucellosis: An Overview,” Emerg Infect Dis 3(2): 213-21, 1997; Ninio, S. and C. R. Roy, “Effector Proteins Translocated by Legionella Pneumophila: Strength in Numbers,” Trends Microbiol. 15(8):372-80, 2007; all of which are hereby incorporated by reference in their entirety). A. tumefaciens uses its group 3 T4SS to deliver oncogenic DNA and proteins into plant cells (Fronzes, R. et al., “The Structural Biology of Type IV Secretion Systems,” Nat Rev Microbiol. 7(10):703-14, 2009; incorporated herein by reference in its entirety).
Genes encoding components of the T4SS are usually arranged in a single or several operons. H. pylori is an example of a bacterium that encodes multiple T4SSs. H. pylori has an effector protein delivery system encoded by the cag pathogenicity island and a DNA release and uptake system encoded by the comB gene cluster (Backert, S. and T. F. Meyer, “Type IV Secretion Systems and Their Effectors in Bacterial Pathogenesis,” Curr Opin Microbiol. 9(2) 207-17, 2006; Smeets, L. C. and Kusters, J. G., “Natural Transformation in Helicobacter Pylori: DNA Transport in an Unexpected Way,” Trends Microbiol. 10(4): 159-62, 2002; all publications incorporated herein by reference in their entirety).
Depending on the structural components that compose a T4SS, the systems can be broadly classified as either type IVA or type IVB systems (Voth, D. E. et al., “Bacterial Type IV Secretion Systems: Versatile Virulence Machines,” Future Microbiol. 7(2):241-57, 2011; incorporated herein by reference in its entirety). A. tumefaciens T4SS and those that resemble it fall into the type IVA secretion systems. The prototypic T-DNA or VirB secretion system of A. tumefaciens is the most well characterized T4SS. The A. tumefaciens T4SS transporter complex and others similar to it typically consist of 11 VirB proteins (encoded by the virB1-virB11 genes) and the coupling protein VirD4, an NTPase (Tegtmeyer, N., S. Wessler and S. Backert, “Role of the Cag-Pathogenicity Island Encoded Type Iv Secretion System in Helicobacter Pylori Pathogenesis,” FEBS J. 278(8):1190-202, 2011; incorporated herein by reference in its entirety). Agrobacterial VirB proteins are grouped into three categories: core components, pilus-associated components and energetic components. T4SSs that fall under the type IV B classification were demonstrated in Legionella pneumophila to consist of twenty-two structural proteins and 5 chaperone proteins (Vogel, J. P. et al., “Conjugative Transfer by the Virulence System of Legionella Pneumophila,” Science 279(5352): 873-6, 1998; Segal, G., M. et al., “Host Cell Killing and Bacterial Conjugation Require Overlapping Sets of Genes within a 22-Kb Region of the Legionella Pneumophila Genome,” Proc Natl Acad Sci. USA 95(4):1669-74, 1998; all publications incorporated herein by reference in their entirety).
Type IVA secretion systems and Type IVB secretion systems recognize different but overlapping translocation signals. A recent study showed that two Brucella effectors can be translocated by L. pneumophila demonstrating that a type IVB secretion system can recognize translocation signals from type IVA secretion system effectors (de Jong, M. F. et al., “Identification of Vcea and Vcec, Two Members of the Vjbr Regulon That Are Translocated into Macrophages by the Brucella Type Iv Secretion System,” Mol Microbiol. 70(6):1378-96, 2008; incorporated herein by reference in its entirety).
The following are examples of T4SS translocation signals. The A. tumefaciens translocation signal resides in a hydrophilic C-terminal region with a consensus R-X(7)-R-X-R-X-R-X-X(n) motif (SEQ ID NO:290) (Vergunst, A. C. et al., “Positive Charge Is an Important Feature of the C-Terminal Transport Signal of the Virb/D4-Translocated Proteins of Agrobacterium,” Proc Natl Acad Sci. USA 102(3):832-7, 2005; incorporated herein by reference in its entirety). Bartonella has a BID domain and a short positively charged tail sequence that together form a bipartite C-terminal translocation signal (Schulein, R. et al., “A Bipartite Signal Mediates the Transfer of Type IV Secretion Substrates of Bartonella Henselae into Human Cells,” Proc Natl Acad Sci. USA 102(3):856-61, 2005; incorporated herein by reference in its entirety). In Helicobacter pylori, there is evidence that both the N- and C-terminal ends of the CagA protein have translocation signals. Hohlfeld et al. observed that residues 6-26 of CagA are important for translocation (Hohlfeld, S. et al., “A C-Terminal Translocation Signal Is Necessary, but Not Sufficient for Type IV Secretion of the Helicobacter Pylori Caga Protein,” Mol Microbiol. 59(5):1624-37, 2006; incorporated herein by reference in its entirety). Hohlfeld et al. also show that CagA translocation depends on the presence of its 20 C-terminal amino acids (Hohlfeld, S. et al., supra).
Type 1, 4, and 5 secretion system genes have also been identified in the MTB Magnetospirillum sp., strain AMB-1 genome by sequence alignments. AMB-1 contains 83 genes that are involved in cell motility and secretion (Matsunaga, T. et al., “Complete genome sequence of the facultative anaerobic magnetotactic bacterium Magnetospirillum sp. AMB-1,” DNA Res. 12:157-166, 2005; incorporated herein by reference in its entirety). There are at least seven genes present in MTB that encode for RTX proteins. Several putative T1SS substrates (YP_420631.1, YP_420638.1, YP_420640.1, YP_421364.1, YP_422662.1, YP_422785.1, and YP_423419.1) have been identified in MTB (M. magneticum AMB-1) (Linhartova et al., “RTX proteins: a highly diverse family secreted by a common mechanism,” FEMS Microbiol. Rev. 34:1076-1112, 2010; incorporated herein by reference in its entirety). These substrates have been annotated as large exoprotein, type 5 secretory pathway, repeats-in-toxin (RTX) toxins and related Ca2+ binding protein, adhesion AidA, and hypothetical protein amb3422 with putative functions such as aminomethyltransferase, adhesion, and cadherin, consistent with type 1 secretion substrates in other bacteria. Exemplary sequences are presented in the Sequence Listing. Moreover, genes responsible for constituting the T1SS complex (such as YP_422838, YP_421739, homolog of E. coli HlyB; E. coli HlyD membrane fusion protein homologs in MTB gi:83311477, 83312258, 83312575, 83313156 with locus tag amb2378; amb3159; amb3476; amb4057; E. coli TolC outer membrane protein homologs in MTB gi:83311344; 83312160; 83312256 with locus tag amb2245; amb3061; amb3157) are present in MTB genome.
FIGS. 1-9 show BLAST alignments of nine MTB proteins that are either secreted or are part of the cells T1SS secretion machinery with the sequenced genes of other α-proteobacteria and other organisms. Each of the sequences, as described by the accession numbers, and the exemplary sequences (e.g., SEQ ID NOS:1-286) can be used in the present invention.
In some embodiments, the protein for secretion can be fused to C-terminal 200 amino acids of YP_420640 (RTX toxins and related Ca2+ binding protein), YP_423419 (RTX toxins and related Ca2+ binding protein), YP_422785 (amb3422), or other MTB T1SS substrates. Alternatively, the proteins in MTB-YP_420502, YP_420631.1, YP_420638.1, YP_420640.1, YP_421364.1, YP_422662.1, YP_422785.1, and YP_423419.1 may be used for the fusion by taking their C-terminus (e.g., the 200 C-terminal amino acids which contains the secretion signal) to target the recombinant fusion protein to the secretion system. An exemplary C-terminal 200 amino acid sequence containing a secretion signal is that of YP_422785, which has the following sequence:







(SEQ ID NO: 291)


DSGTGWIWDPTLNGTSLSVTAHAATTVNGNSTYNGGATADYVIGLGQNE


 


MVHLGGGADVYAGHGSYNTIGVSDMNFHFLDGGAGGGNTLQWENLNNQA


 


FDLTGLWNNAVQNFDVLDLSHANNNNAVLDLAHLQSMLNGTNAVTGTGN


 


ALVVIGGNSVTLAGSGWQANGTAELTVNGQHDSYTQYSNGDTHVYVENH


 


THVG






As illustrated by the foregoing, bacteria use diverse machinery to secrete proteins as a means for interacting with their environment, which in case of endosymbionts, includes the environment of the host cell. In some embodiments, the present invention modifies the morphology or the physiology of the host cell (as well as organism) via protein(s), nucleic acid(s), and/or other factor(s) secreted from the artificial endosymbiont through a secretion system.
Modified Artificial Endosymbionts
In some embodiments, the artificial endosymbionts, such as α-proteobacteria, are modified to achieve a higher level of recombinant protein secretion. Methods for genetically modifying artificial endosymbionts can use methods well known in the art for recombinantly modifying single celled organisms. Typically, the artificial endosymbiont is genetically modified to improve secretion of target molecules from the artificial endosymbiont into the host cell. Alternatively, the artificial endosymbiont is engineered to increase transport of a target molecule from the host into the artificial endosymbiont. Modifications may also involve increasing production of proteins or RNA through changing promoter or ribosome binding sequences, or deleting or silencing of certain genes in the artificial endosymbiont.
In some embodiments, the flagellar proteins of an artificial endosymbiont are modified so that the flagellar proteins are no longer expressed. Flagellar proteins have high homology to bacterial secretion systems suggesting a common evolutionary ancestor. In some embodiments, the flagellar proteins of an artificial endosymbiont are modified to create a secretion system. In some embodiments, the single-celled organism is modified so that it can no longer synthesize an essential molecule that is preferably provided by the eukaryotic host cell. In some embodiments, the single-celled organism is genetically modified so that its cell cycle is coordinated with the cell cycle of the eukaryotic host cell so that copy number of the single-celled organism can be maintained at a sufficient level to impart the phenotype to daughter cells.
Molecular biology tools have been developed for genetic manipulations of MTB most extensively in AMB-1 and M. gryphiswaldense strain MSR-1 (reviewed in Jogler, C. and Schtiler, D. in Magnetoreception and Magnetosomes in Bacteria, New York, Springer, p 134-138, 2007; incorporated herein by reference). The genomes of two other Magnetospirillum strains and Magnetococcus sp. strain MC-1 have also been recently sequenced. In some embodiments, genes from these strains or other MTB strains, presently culturable or unculturable, sequenced or unsequenced, know or unknown, can be used in the present invention.
Several engineering approaches are used to modify artificial endosymbionts, including: (1) engineering into the artificial endosymbiont dedicated secretion systems that naturally exist in other bacteria; (2) engineering cell envelope mutations into the artificial endosymbiont so that it alters the outer membrane or peptidoglycan layer permeability (e.g., Shin, H. and Chen, R. R., “Extracellular recombinant protein production from and Escherichia coli 1pp deletion mutant,” Biotechnol Bioeng. 101:1288-96, 2008; incorporated herein by reference in its entirety); and (3) co-expression of a lysis-promoting protein that removes the outer membrane (Ni, Y. and Chen, R., “Extracellular recombinant protein production from and Escherichia coli,” Biotechnol Lett. 31:1661-70, 2009; incorporated herein by reference in its entirety).
In some embodiments, the E. coli α-haemolysin transporter genes HlyB and HlyD are recombinantly expressed in the artificial endosymbiont. Target proteins are then engineered by fusing them with T1SS substrate secretion signal, which is located in C-terminal of HlyA to target them to the α-haemolysin transporter system. The HlyA secretion signal comprises:







(SEQ ID NO: 292)


GNSLAKNVLSGGKGNDKLYGSEGADLLDGGEGNDLLKGGYGNDIYRYLS


 


GYGHHIIDDDGGKDDKLSLADIDFRDVAFRREGNDLIMYKAEGNVLSIG


 


HKNGITFRNWFEKESGDISNHQIEQIFDKDGRVITPDSLKKALEYQQSN


 


NKASYVYGNDALAYGSQDNLNPLINEISKIISAAGNFDVKEERAAASLL


 


QLSGNASDFSYGRNSITLTASA.






In some embodiments, the T1SS from Pseudomonas fluorescens is used to transport recombinant proteins. The T1SS genes such as TliA for the lipase ABC transporter are engineered into the artificial endosymbiont. The target protein is fused N-terminally to a 104 residue, minimal region comprising:







(SEQ ID NO: 293)


GSDGNDLIQGGKGADFIEGGKGNDTIRDNSGHNTFLFSGHFGQDRIIGY


 


QPTDRLVFQGADGSTDLRDHAKAVGADTVLSFGADSVTLVGVGLGGLWS


 


EGVLIS.






This fusion of target protein and minimal region allows secretion of recombinant protein. It is interesting to note that there are several proteins exhibiting substantial sequence homology to P. fluorescens lipase TliA such as YP_420640, YP_422785, YP_421364, YP_420631, and others that are present in the MTB genome (see, e.g., FIG. 9 and sequences in Sequence Listing). Most of this homology is located in the C-terminal domain of the proteins, which contains the transport signal. In some embodiments, the MTB lipase ABC transport system is used to transport recombinant proteins by fusing target protein to a C-terminal signal of MTB lipase ABC transport system substrates (also see FIG. 9, accession numbers and corresponding sequences in the Sequence Listing for sequence homology). In some embodiments, the C-terminal signal sequence comprises:







(SEQ ID NO: 294)


GAIGGAGAIPGITLVGNAGNDDIIGTNGNDLLLGGKGGATYRFSGGGCG


 


SGGGWSIVQSDINDVISAGAGDDVIYGDARLVNGNIQITGSGNDVLDGG


 


SGNDQIHGGAGNDTIIGGTGDDVMFGDQGNDTFLFDFGFGHDVVDGGRG


 


SNWTDTLDLTHDNQISSVNIEGVSGWAVSVDAQGHHVAQATNGAHDANG


 


TIVVTNHDGSQDTIEFHNVEKVVW.






In some embodiments, the RaxA, RaxB and RaxC genes of Xanthomonas oryzae pv. oryzae are recombinantly expressed in the artificial endosymbiont. The target protein is fused to RaxST, which is the recognition sequence for the RaxABC secretory system. In some embodiments, the RaxST recognition sequence comprises:







(SEQ ID NO: 295)


MLMGMSEEHPSNVQIDDAQRVRLLRAVFDAYYQNRQELGTVFDTNRAWC


 


SRLTGLARLFPRSRMICCVRDVGWIVDSFERLAQSQPLRLSALFGYDPE


 


DSVSMHADLLTAPRGVVGYALDGLRQAFYGDHADRLLLLRYDTLAQRPA


 


QAMEQVYAFLQLPAFAHDYAGVQAEAERFDAALQMPGLHRVRRGVHYVP


 


RRSVLPPALFDQLQELAFWESAPSHGALLV.






In some embodiments, the target protein is fused at the N-terminal end to a Sec-dependent signal sequence, and the C-terminal end of the target protein is fused to a β-motif. Translocation of such target protein fusions is a two-step process. The target protein is transported into the periplasm using Sec-dependent transport, whereupon the β-motif forms a transmembrane pore in the outer-membrane through which the target protein is secreted from the periplasmic space. The β-motif is cleaved, allowing translocation of the target protein.
In some embodiments, the target protein is fused to an autotransporter (target protein replaced the passenger domain region (29 to 685 amino acids), such as the YfaL autotransporter (Ko, H. J. et al., “Functional cell surface display and controlled secretion of diverse agarolytic enzymes by Escherichia coli with a novel ligation-independent cloning vector based on the autotransporter YfaL,” App Environ Microbiol. 78:3051-3058, 2012; incorporated herein by reference in its entirety). The YfaL autotransporter sequence comprises:







(SEQ ID NO: 296)


MRIIFLRKEYLSLLPSMIASLFSANGVAAVTDSCQGYDVKASCQASRQS


 


LSGITQDWSIADGQWLVFSDMTNNASGGAVFLQQGAEFSLLPENETGMT


 


LFANNTVTGEYNNGGAIFAKENSTLNLTDVIFSGNVAGGYGGAIYSSGI


 


NDTGAVDLRVTNAMFRNNIANDGKGGAIYTINNDVYLSDVIFDNNQAYT


 


STSYSDGDGGAIDVTDNNSDSKHPSGYTIVNNTAFTNNTAEGYGGAIYT


 


NSVTAPYLIDISVDDSYSQNGGVLVDENNSAAGYGDGPSSAAGGFMYLG


 


LSEVTFDIADGKTLVIGNTENDGAVDSIAGTGLITKTGSGDLVLNADNN


 


DFTGEMQIENGEVTLGRSNSLMNVGDTHCQDDPQDCYGLTIGSIDQYQN


 


QAELNVGSTQQTFVHALTGFQNGTLNIDAGGNVTVNQGSFAGIIEGAGQ


 


LTIAQNGSYVLAGAQSMALTGDIVVDDGAVLSLEGDAADLTALQDDPQS


 


IVLNGGVLDLSDFSTWQSGTSYNDGLEVSGSSGTVIGSQDVVDLAGGDN


 


LHIGGDGKDGVYVVVDASDGQVSLANNNSYLGTTQIASGTLMVSDNSQL


 


GDTHYNRQVIFTDKQQESVMEITSDVDTRSDAAGHGRDIEMRADGEVAV


 


DAGVDTQWGALMADSSGQHQDEGSTLIKTGAGTLELTASGTTQSAVRVE


 


EGTLKGDVADILPYASSLWVGDGATFVTGADQDIQSIDAISSGTIDISD


 


GTVLRLTGQDTSVALNASLFNGDGILVNATDGVILTGELNINLETDSLT


 


YLSNVTVNGNLTNTSGAVSLQNGVAGDTLTVNGDYTGGGTLLLDSELNG


 


DDSVSDQLVMNGNTAGNITVVVNSITGIGEPTSTGIKVVDFAADPTQFQ


 


NNAQFSLAGSGYVNMGAYDYTLVEDNNDWYLRSQEVTPPSPPDPDPTPD


 


PDPTPDPDPTPDPEPTPAYQPVLNAKVGGYLNNLRAANQAFMMERRDHA


 


GGDGQTLNLRVIGGDYHYTAAGQLAQHEDTSTVQLSGDLFSGRWGTDGE


 


WMLGIVGGYSDNQGDSRSNMTGTRADNQNHGYAVGLTSSWFQHGNQKQG


 


AWLDSWLQYAWFSNDVSEQEDGTDHYHSSGIIASLEAGYQWLPGRGVVI


 


EPQAQVIYQGVQQDDFTAANRARVSQSQGDDIQTRLGLHSEWRTAVHVI


 


PTLDLNYYHDPHSTEIEEDGSTISDDAVKQRGEIKVGVTGNISQRVSLR


 


GSVAWQKGSDDFAQTAGFLSMTVKW.






In some embodiments, a protease is included to cleave the β-motif from the target protein, such as for example, a tobacco etch virus protease, E. coli serine protease Pet, and serine protease autotransporters of the Enterobacteriaceae (SPATEs), that releases passenger domain from the β-domain, without requiring exogenous protease. In some embodiments, an E. coli autotransporter Antigen 43 (Ag43) is used with the target protein. The Antigen 43 autotransporter sequence comprises:







(SEQ ID NO: 297)


MKRHLNTCYRLVWNHMTGAFVVASELARARGKRGGVAVALSLAAVTSLP


 


VLAADIVVHPGETVNGGTLANHDNQIVFGTTNGMTISTGLEYGPDNEAN


 


TGGQWVQDGGTANKTTVTSGGLQRVNPGGSVSDTVISAGGGQSLQGRAV


 


NTTLNGGEQWMHEGAIATGTVINDKGWQVVKPGTVATDTVVNTGAEGGP


 


DAENGDTGQFVRGDAVRTTINKNGRQIVRAEGTANTTVVYAGGDQTVHG


 


HALDTTLNGGYQYVHNGGTASDTVVNSDGWQIVKNGGVAGNITVNQKGR


 


LQVDAGGTATNVILKQGGALVISTAATVTGINRLGAFSVVEGKADNVVL


 


ENGGRLDVLIGHTATNTRVDDGGTLDVRNGGTATTVSMGNGGVLLADSG


 


AAVSGTRSDGKAFSIGGGQADALMLEKGSSFTLNAGDTATDTTVNGGLF


 


TARGGTLAGTTTLNNGAILTLSGKTVNNDTLTIREGDALLQGGSLTGNG


 


SVEKSGSGTLTVSNTTLTQKAVNLNEGTLTLNDSTVTTDVIAQRGTALK


 


LTGSTVLNGAIDPINVTLASGATWNIPDNATVQSVVDDLSHAGQIHFTS


 


TRTGKFVPATLKVKNLNGQNGTISLRVRPDMAQNNADRLVIDGGRATGK


 


TILNLVNAGNSASGLATSGKGIQVVEAINGATTEEGAFVQGNRLQAGAF


 


NYSLNRDSDESWYLRSENAYRAEVPLYASMLTQAMDYDRIVAGSRSHQT


 


GVNGENNSVRLSIQGGHLGHDNNGGIARGATPESSGSYGFVRLEGDLMR


 


TEVAGMSVTAGVYGAAGHSSVDVKDDDGSRAGTVRDDAGSLGGYLNLVH


 


ISSGLWADIVAQGTRHSMKASSDNNDFRARGWGWLGSLETGLPFSITDN


 


LMLEPQLQYTWQGLSLDDGKDNAGYVKFGHGSAQHVRAGFRLGSHNDMT


 


FGEGTSSRAPLRDSAKHSVSELPVNWWVQPSVIRTFSSRGDMRVGTSTA


 


GSGMTFSPSQNGTSLDLQAGLEARVRENITLGVQAGYAHSVSGSSAEGY


 


NGQATLNVTF.






In some embodiments, the translocase of the outer mitochondrial membrane (TOM complex) is engineered into the artificial endosymbiont. The TOM complex includes the receptors Tom20, Tom22, Tom70 and the channel-forming protein Tom40, and several other small subunits (reviewed in Hoogenraad, N. J. et al., Biochem Biophy Acta 1592: 97-105, 2002; Neupert W. and Herrmann, J. M., Annu Rev Biochem. 76:723-749, 2007; and Chacinska, A. et al., Cell 138:628-44, 2009; all publications incorporated herein by reference). Tom20 recognizes the substrate and transfers to centrally located Tom22, where the substrate is inserted into the Tom40 channel. Upon substrate import, TOM complex forms a complex with the translocase of the inner membrane (TIM complex) (Chacinska, A. et al., EMBO J 22:5370-81, 2003; incorporated herein by reference). The TIM complex consists of four integral membrane proteins, Tim23, Tim17, Tim50, and Tim21. Tim23 forms the protein-conducting channel of the translocase and is tightly associated with Tom17, whereas, Tim50 acts as regulator for the Tim23 channel and Tim21 transiently interacts with the TOM complex via Tom22 (Milisav, I. et al., “Modular structure of the Tim23 preprotein translocase of mitochondria,” J Biol Chem. 276:25856-25861, 2001; incorporated herein by reference).
Nucleic Acids
In another aspect, the present invention relates to the nucleic acids that encode, at least in part, the individual peptides, polypeptides and proteins secreted in the methods of the present invention. In some embodiments, the nucleic acids may be natural, synthetic or a combination thereof. In some embodiments, the nucleic acids of the invention also include the nucleic acids that are secreted from the artificial endosymbiont into the host cell. The nucleic acids of the invention may be RNA, mRNA, DNA or cDNA.
In some embodiments, the nucleic acids of the invention also include expression vectors, such as plasmids, or viral vectors, or linear vectors, or vectors that integrate into chromosomal DNA. Expression vectors can contain a nucleic acid sequence that enables the vector to replicate in one or more selected host cells. Such sequences are well known for a variety of cells. The origin of replication from the plasmid pBR322 is suitable for most Gram-negative bacteria. In eukaryotic host cells, e.g., mammalian cells, the expression vector can be integrated into the host cell chromosome and then replicate with the host chromosome. Similarly, vectors can be integrated into the chromosome of prokaryotic cells.
Expression vectors also generally contain a selection gene, also termed a selectable marker. Selectable markers are well-known in the art for prokaryotic and eukaryotic cells, including host cells of the invention. Generally, the selection gene encodes a protein necessary for the survival or growth of transformed host cells grown in a selective culture medium. Host cells not transformed with the vector containing the selection gene will not survive in the culture medium. Typical selection genes encode proteins that (a) confer resistance to antibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate, or tetracycline, (b) complement auxotrophic deficiencies, or (c) supply critical nutrients not available from complex media, e.g., the gene encoding D-alanine racemase for Bacilli. In some embodiments, an exemplary selection scheme utilizes a drug to arrest growth of a host cell. Those cells that are successfully transformed with a heterologous gene produce a protein conferring drug resistance and thus survive the selection regimen. Other selectable markers for use in bacterial or eukaryotic (including mammalian) systems are well-known in the art. In some embodiments, the selectable marker is the target protein or encoded by the nucleic acid secreted by the artificial endosymbiont into the host cell.
In some embodiments, the expression vector for producing a heterologous polypeptide also contains a promoter, which can be a constitutive or an inducible promoter, that is recognized by the host RNA polymerase and is operably linked to the nucleic acid encoding the target protein. Inducible or constitutive promoters (or control regions) with suitable enhancers, introns, and other regulatory sequences are well-known in the art.
In some embodiments, it may be desirable to modify the polypeptides of the present invention. One of skill will recognize many ways of generating alterations in a given nucleic acid construct to generate variant polypeptides Such well-known methods include site-directed mutagenesis, PCR amplification using degenerate oligonucleotides, exposure of cells containing the nucleic acid to mutagenic agents or radiation, chemical synthesis of a desired oligonucleotide (e.g., in conjunction with ligation and/or cloning to generate large nucleic acids) and other well-known techniques (see, e.g., Gillam and Smith, Gene 8:81-97, 1979; Roberts et al., Nature 328:731-734, 1987).
In some embodiments, the recombinant nucleic acids encoding the polypeptides of the invention are modified to provide preferred codons which enhance translation of the nucleic acid in a selected organism.
The polynucleotides of the invention also include polynucleotides including nucleotide sequences that are substantially equivalent to the polynucleotides of the invention. Polynucleotides according to the invention can have at least about 80%, more typically at least about 90%, and even more typically at least about 95%, sequence identity to a polynucleotide of the invention. The invention also provides the complement of the polynucleotides including a nucleotide sequence that has at least about 80%, more typically at least about 90%, and even more typically at least about 95%, sequence identity to a polynucleotide encoding a polypeptide recited above. The polynucleotide can be DNA (genomic, cDNA, amplified, or synthetic) or RNA. Methods and algorithms for obtaining such polynucleotides are well known to those of skill in the art and can include, for example, methods for determining hybridization conditions which can routinely isolate polynucleotides of the desired sequence identities.
Nucleic acids which encode protein analogs or variants in accordance with this invention (i.e., wherein one or more amino acids are designed to differ from the wild type polypeptide) may be produced using site directed mutagenesis or PCR amplification in which the primer(s) have the desired point mutations. For a detailed description of suitable mutagenesis techniques, see Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989) and/or Current Protocols in Molecular Biology, Ausubel et al., eds, Green Publishers Inc. and Wiley and Sons, N.Y (1994). Chemical synthesis using methods well known in the art, such as that described by Engels et al., Angew Chem Intl Ed. 28:716-34, 1989, may also be used to prepare such nucleic acids.
In some embodiments, the nucleic acids encode a variant (i.e., recombinant variant) of the polypeptides of the present invention. As used herein “variant” or “recombinant variant” refers to any polypeptide differing from naturally occurring polypeptides by amino acid insertions, deletions, and substitutions, created using recombinant DNA techniques. Guidance in determining which amino acid residues may be replaced, added, or deleted without abolishing activities of interest, such as enzymatic or binding activities, may be found by comparing the sequence of the particular polypeptide with that of homologous peptides and minimizing the number of amino acid sequence changes made in regions of high homology.
In some embodiments, amino acid “substitutions” for creating variants are preferably the result of replacing one amino acid with another amino acid having similar structural and/or chemical properties, i.e., conservative amino acid replacements Amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipathic nature of the residues involved. For example, nonpolar (hydrophobic) amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan, and methionine; polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine, and glutamine; positively charged (basic) amino acids include arginine, lysine, and histidine; and negatively charged (acidic) amino acids include aspartic acid and glutamic acid.
In some embodiments, amino acid “insertions” or “deletions” for the variants are typically in the range of about 1 to 5 amino acids. The variation allowed may be experimentally determined by systematically making insertions, deletions, or substitutions of amino acids in a polypeptide molecule using recombinant DNA techniques and assaying the resulting recombinant variants for activity.
Alternatively, in some embodiments, where alteration of function is desired, insertions, deletions or non-conservative alterations can be engineered in the nucleic acid to produce altered polypeptides or chimeric polypeptides, e.g., variant polypeptides. Such alterations can, for example, alter one or more of the biological functions or biochemical characteristics of the polypeptides of the invention. For example, such alterations may change polypeptide characteristics such as ligand-binding affinities or degradation/turnover rate. Further, such alterations can be selected so as to generate polypeptides that are better suited for expression, scale up, and the like in the host cells chosen for expression.
Alternatively, recombinant nucleic acids encoding these same or similar polypeptides may be synthesized or selected by making use of the “redundancy” in the genetic code. Various codon substitutions, such as the silent changes which produce various restriction sites, may be introduced to optimize cloning into a plasmid or viral vector or expression in a particular prokaryotic or eukaryotic system. Mutations in the polynucleotide sequence may be reflected in the polypeptide or domains of other peptides added to the polypeptide to modify the properties of any part of the polypeptide, to change characteristics such as ligand-binding affinities, or degradation/turnover rate.
In some embodiments, nucleic acid or polynucleotides encoding the novel nucleic acids are changed via site-directed mutagenesis. This method uses oligonucleotide sequences that encode the polynucleotide sequence of the desired amino acid variant, as well as a sufficient adjacent nucleotide on both sides of the changed amino acid to form a stable duplex on either side of the site of being changed. In general, the techniques of site-directed mutagenesis are well known to those of skill in the art and this technique is exemplified by publications such as, Edelman et al., DNA 2:183, 1983. A versatile and efficient method for producing site-specific changes in a polynucleotide sequence is described in Zoller and Smith, Nucleic Acids Res. 10:6487-500, 1982.
In some embodiments, PCR may also be used to create amino acid sequence variants of the novel nucleic acids. When small amounts of template DNA are used as starting material, primer(s) that differs slightly in sequence from the corresponding region in the template DNA can generate the desired amino acid variant. PCR amplification results in a population of product DNA fragments that differ from the polynucleotide template encoding the target at the position specified by the primer. The product DNA fragments replace the corresponding region in the plasmid and this gives the desired amino acid variant.
A further technique for generating amino acid variants is the cassette mutagenesis technique described in Wells et al., Gene 34:315, 1985; and other mutagenesis techniques well known in the art, such as, for example, the mutagenesis techniques described in Sambrook et al., supra, and Current Protocols in Molecular Biology, referenced herein.
Host Cells
In another aspect, the present invention provides a eukaryotic host cell containing an artificial endosymbiont, wherein the artificial endosymbiont imparts a phenotype to the host cell by secreting proteins, nucleic acids, and/or other factors from the artificial endosymbiont into the host cell. In some embodiments, the artificial endosymbiont is heritable.
In the present invention, various eukaryotic cells can be used as the host cell. In some embodiments, the host cells of the invention are animal cells. In some embodiments, the host cells are mammalian cells, such as that of mouse, rat, rabbit, hamster, porcine, bovine, feline, or canine. In some embodiments, the mammalian cells are cells of primates, including but not limited to, monkeys, chimpanzees, gorillas, and humans. In some embodiments, the mammalians cells are mouse cells, as mice routinely function as a model for other mammals, most particularly for humans (see, e.g., Hanna, J. et al., “Treatment of sickle cell anemia mouse model with iPS cells generated from autologous skin,” Science 318:1920-23, 2007; Holtzman, D. M. et al., “Expression of human apolipoprotein E reduces amyloid-β deposition in a mouse model of Alzheimer's disease,” J Clin Invest. 103(6):R15-R21, 1999; Warren, R. S. et al., “Regulation by vascular endothelial growth factor of human colon cancer tumorigenesis in a mouse model of experimental liver metastasis,” J Clin Invest. 95: 1789-1797, 1995; each publication incorporated herein by reference) Animal cells include, for example, fibroblasts, epithelial cells (e.g., renal, mammary, prostate, lung), keratinocytes, hepatocytes, adopicytes, endothelial cells, hematopoietic cells. In some embodiments, the animal cells are adult cells (e.g., terminally differentiated, dividing or non-dividing) or embryonic cells (e.g., blastocyst cells, etc.).
In some embodiments, the host cell is a cancer cell, including human cancer cells. Many cancer cell lines that are well known to those of ordinary skill in the art can be used as a host cell, including common epithelial tumor cell lines such as Coco-2, MDA-MB231 and MCF7, and non-epithelial tumor cell lines, such as HT-1080 and HL60, the NCI60-cell line panel (see, e.g., Shoemaker, R., “The NCI60 human tumor cell line anticancer drug screen,” Nature Reviews Cancer 6:813-23, 2006; incorporated herein by reference). Additionally, those of ordinary skill in the art are familiar with obtaining cancer cells from primary tumors. Cancer cells also include, for example, solid tumor cell types, hematopoietic cancer cells, carcinomas, sarcomas, leukemias, lymphomas, gliomas, as well as specific tissue related cancers such as prostate cancer, breast cancer, lung cancer, colorectal cancer, pancreatic cancer, melanoma, glioblastoma, liver cancer, and the NCI 60 panel of cancer cell lines.
In some embodiments, the host cells are stem cells. Variety of stem cells types are known in the art and can be used as host cells, including for example, embryonic stem cells, inducible pluripotent stem cells, hematopoietic stem cells, neural stem cells, epidermal neural crest stem cells, mammary stem cells, intestinal stem cells, mesenchymal stem cells, olfactory adult stem cells, testicular cells, and progenitor cells (e.g., neural, angioblast, osteoblast, chondroblast, pancreatic, epidermal, etc.).
In some embodiments, the host cell is a cell found in the circulatory system of a mammal, including humans. Exemplary circulatory system cells include, among others, red blood cells, platelets, plasma cells, T-cells, natural killer cells, or the like, and precursor cells of the same. As a group, these cells are defined to be circulating host cells of the invention. The present invention may be used with any of these circulating cells. In some embodiments, the host cell is a T-cell. In some embodiments, the host cell is a B-cell. In some embodiments, the host cell is a neutrophil. In some embodiments, the host cell is a megakaryocyte.
In some embodiments, the host cell is a plant cell. In some embodiments, the host cells are cells of monocotyledonous or dicotyledonous plants including, but not limited to, maize, wheat, barley, rye, oat, rice, soybean, peanut, pea, lentil and alfalfa, cotton, rapeseed, canola, pepper, sunflower, potato, tobacco, tomato, eggplant, eucalyptus, a tree, an ornamental plant, a perennial grass, or a forage crop. In some embodiments, the host cells are algal, including but not limited to algae of the genera Chlorella, Chlamydomonas, Scenedesmus, Isochrysis, Dunaliella, Tetraselmis, Nannochloropsis, or Prototheca. In some embodiments, the host cells are fungi cells, including but not limited to, fungi of the genera Saccharomyces, Klyuveromyces, Candida, Pichia, Debaromyces, Hansenula, Yarrowia, Zygosaccharomyces, or Schizosaccharomyces. 
In some embodiments, at least one gene from the host cell is genetically altered. In some embodiments, mutual nutritional dependence (biotrophy) may be established between the artificial endosymbiont and the host cell by genetic modification of the host cell, using the appropriate molecular biology techniques specific to the target host cell type known to those of ordinary skill in the art, to create host cell dependence on the artificial endosymbiont for some essential macromolecule thus establishing the environmental pressures for biotrophy. In some embodiments, nutritional dependence for an artificial endosymbiont on the host cell can be established by genetically altering the host cell to eliminate the ability of the host cell to synthesize various metabolites, cofactors, vitamins, nucleotides, or other essential molecules. In such embodiments, the essential molecule may be provided by the artificial endosymbiont. For example, an exemplary host cell gene for modification is the gene encoding the enzyme serine hydroxymethyltransferase, which converts serine into glycine at the terminus of the 3-phosphoglycerate biosynthetic pathway for amino acid production. Inactivation of this gene in the host cell would create a host cell dependent on or favoring an artificial endosymbiont that produces glycine.
Methods of Introducing Artificial Endosymbionts into Host Cells
The single-celled organisms of the invention can be introduced into host cells by a number of methods known to those of skill in the art including, but not limited to, microinjection, natural phagocytosis, induced phagocytosis, macropinocytosis, other cellular uptake processes, liposome fusion, erythrocyte ghost fusion, electroporation, receptor mediated methods, and the like (see, e.g., Microinjection and Organelle Transplantation Techniques, Celis et al., eds., Academic Press, New York (1986), and references cited therein; incorporated herein by reference in its entirety).
In some embodiments, a single-celled organism is introduced into the host cell by microinjection into the cytoplasm of the host cell. A variety of microinjection techniques are known to those skilled in the art. Microinjection is an efficient transfer technique (essentially 100%) and has no cell type restrictions (Id.; Xi, Z. and Dobson, S., “Characterization of Wolbachia transfection efficiency by using microinjection of embryonic cytoplasm and embryo homogenate,” Appl Environ Microbiol. 71(6):3199-204, 2005; Goetz, M. et al., “Microinjection and growth of bacteria in the cytosol of mammalian host cells,” Proc Natl Acad Sci. USA 98:12221-6, 2001; each publication incorporated herein by reference).
Naturally phagocytotic cells have been show to take up bacteria, including MTB (Burdette, D. L. et al., “Vibrio VopQ induces PI3-kinase independent autophagy and antagonizes phagocytosis,” Mol Microbiol. 73:639, 2009; Wiedemann, A. et al., “Yersinia enterocolitica invasin triggers phagocytosis via β1 integrins, CDC42Hs and WASp in macrophages,” Cell Microbiol. 3:693, 2001; Hackam, D. J. et al., “Rho is required for the initiation of calcium signaling and phagocytosis by Fcγ receptors in macrophages,” J Exp Med. 186(6):955-66, 1997; Matsunaga, T. et al., “Phagocytosis of bacterial magnetite by leucocytes. Appl Microbiol Biotech. 31(4): 401-5, 1989; all publications incorporated herein by reference).
In some embodiments, non-phagocytotic cell types can be induced to endocytose bacteria by co-culturing with various factors: media, chemical factors, and biologic factors (e.g., baculovirus, protein factors, genetic knock-ins, etc.) (see, e.g., Salminen, M. et al., “Improvement in nuclear entry and transgene expression of baculoviruses by disintegration of microtubules in human hepatocytes,” J Virol. 79(5):2720-8, 2005; Modalsli, K. R. et al., “Microinjection of HEp-2 cells with coxsackie B1 virus RNA enhances invasiveness of Shigella flexneri only after prestimulation with UV-inactivated virus,” APMIS 101:602-6, 1993; Hayward, R. D. and Koronakis, V., “Direct nucleation and bundling of actin by the SipC protein of invasive Salmonella,” EMBO J. 18:4926-34, 1999; Yoshida, S. et al., “Shigella deliver an effector protein to trigger host microtubule destabilization, which promotes Rac1 activity and efficient bacterial internalization,” EMBO J. 21: 2923-35, 2002; Bigildeev et al., Exp Hematol. 39:187, 2011; Finlay, B. B. and Falkow, S., “Common themes in microbial pathogenicity revisited. Microbiol Mol Biol Rev. 61:136-69, 1997; each publication incorporated herein by reference in its entirety).
In some embodiments, the related process of macropinocytosis or “cell drinking,” a method numerous bacteria and viruses employ for intracellular entry, can be used to introduce the artificial endosymbiont into the host cell (Zhang, In: Molecular Imaging and Contrast Agent Database (MICAD) [database online] (2004); Bethesda (Md.): National Library of Medicine (US), NCBI 2004-2011; each publication incorporated herein by reference). Various protocols can be employed to induce cells to take up bacteria. Several agents, such as nucleic acids, proteins, drugs and organelles have been encapsulated in liposomes and delivered to cells (Ben-Haim, N. et al., “Cell-specific integration of artificial organelles based on functionalized polymer vesicles,” Nano Lett. 8(5):1368-73, 2008; Lian, W. et al., “Intracellular delivery can be achieved by bombarding cells or tissues with accelerated molecules or bacteria without the need for carrier particles,” Exp Cell Res. 313(1):53-64, 2007; Heng, B. C. and Cao, T, “Immunoliposome-mediated delivery of neomycin phosphotransferase for the lineage-specific selection of differentiated/committed stem cell progenies: Potential advantages over transfection with marker genes, fluorescence-activated and magnetic affinity cell-sorting,” Med. Hypotheses 65(2):334-6, 2005; Potrykus, Ciba Found Symp. Vol. 1 54:198, 1990; each publication incorporated herein by reference). This method is inexpensive, relatively simple and scalable. Additionally, liposome uptake can be enhanced by manipulation of incubation conditions, variation of liposome charge, receptor mediation, and magnetic enhancement (see, e.g., Pan et al., Int J Pharm. 358:263, 2008; Sarbolouki, M. N. and Toliat, T., “Storage stability of stabilized MLV and REV liposomes containing sodium methotrexate (aqueous & lyophilized),” J Pharm Sci Techno. 52(10):23-27, 1998; Elorza, B. et al., “Comparison of particle size and encapsulation parameters of three liposomal preparations.” J Microencapsul. 10(2):237-48, 1993; Mykhaylyk, O. et al., “Liposomal Magnetofection,” Methods Mol Bio. 605:487-525, 2010; each publication incorporated herein by reference).
Erythrocyte-mediated transfer is similar to liposome fusion and has been shown to have high efficiency and efficacy across all cell types tested (Microinjection and Organelle Transplantation Techniques; Celis et al. Eds.; Academic Press: New York (1986), incorporated herein by reference). Typically erythrocytes are loaded by osmotic shock methods or electroporation methods (Schoen, P. et al., “Gene transfer mediated by fusion protein hemagglutinin reconstituted in cationic lipid vesicles,” Gene Therapy 6:823-32, 1999; Li, L. H. et al., “Electrofusion between heterogeneous-sized mammalian cells in a pellet: potential applications in drug delivery and hybridoma formation,” Biophysical J. 71:479-86, 1996; Carruthers, A. and Melchior, D. L., “A rapid method of reconstituting human erythrocyte sugar transport proteins,” Biochemistry 23:2712-18, 1984; each publication incorporated herein by reference). Alternatively, erythrocytes may be loaded indirectly by loading hematopoietic progenitors with single-celled organisms and inducing them to differentiate and expand into erythrocytes containing single-celled organisms.
In some embodiments, electroporation, a commonly used, inexpensive method to deliver factors to cells, can be used to introduce artificial endosymbionts into host cells (Potrykus, I., “Gene transfer methods for plants and cell cultures,” Ciba Found Symp 154:198-208; discussion 208-112, 1990; Wolbank, S. et al., “Labeling of human adipose-derived stem cells for non-invasive in vivo cell tracking,” Cell Tissue Bank 8:163-177, 2007; each publication incorporated herein by reference).
In some embodiments, a host cell that naturally endocytoses bacteria (e.g., Chinese hamster ovary (CHO) is used. In some embodiments, the modified single-celled bacteria are added to the CHO culture directly. CHO cells are cultured by standard procedures, such as in Ham's F-12 media with 10% fetal calf serum media, prior to infection with the MTB. Post infection, the media is augmented with additional iron (40 to 80 μM) as either ferric malate or FeCl3. Numerous other cell types internalize bacteria by endocytosis or more specifically phagocytosis; endosymbionts or parasites have their own methods for cellular entry, and these natural processes can be exploited for internalization of the artificial endosymbionts resulting in the generation of so-called symbiosomes. In some embodiments, symbiosomes from one cell can be transplanted to another cell type (i.e., one incapable of endocytosis of artificial endosymbionts) using microinjection, organelle transplantation, and chimera techniques. These host cells are cultured in typical media and with the techniques for the specific cell type.
In some embodiments, a single-celled organism is introduced to the host cell by a liposome mediated process. Mitochondria and chloroplasts, which are larger than MTB, have been efficiently introduced into eukaryotic cells when encapsulated into liposomes (see, e.g., Bonnett, H. T., Planta 131:229, 1976; Giles, K. et al., “Liposome-mediated uptake of chloroplasts by plant protoplasts,” In Vitro Cellular & Developmental Biology—Plant 16(7):581-584; each publication incorporated herein by reference). Numerous liposome fusion protocols and agents are available and can be used by the skilled artisan without undue experimentation (see, e.g., Ben-Haim, N. et al., “Cell-specific integration of artificial organelles based on functionalized polymer vesicles,” Nano Lett. 8(5):1368-73, 2008; Lian, W. et al., “Intracellular delivery can be achieved by bombarding cells or tissues with accelerated molecules or bacteria without the need for carrier particles,” Experimental Cell Research 313(1):53-64, 2007; Heng, B. C. and Cao, T., “Immunoliposome-mediated delivery of neomycin phosphotransferase for the lineage-specific selection of differentiated/committed stem cell progenies: Potential advantages over transfection with marker genes, fluorescence-activated and magnetic affinity cell-sorting,” Med. Hypotheses 65(2):334-6, 2005; Potrykus, Ciba Found Symp, Vol. 1 54:198, 1990; each publication incorporated herein by reference).
Use of Reprogrammed Host Cells
The artificial endosymbionts of the present invention introduce into host cells peptides/proteins, nucleic acids, and/or other factors. These proteins, nucleic acids, or other factors can alter gene transcription or translation, post translational modifications, host cell differentiation, remodeling, proliferation, sensitivity or response to external and/or internal stimuli, metabolic, anabolic or other biochemical processes. In some embodiments, the artificial endosymbiont can control host cells through expression, availability, and delivery of certain transcription factors, growth factors, cytokines, signaling pathway molecules, or other recombinant proteins. The artificial endosymbiont may also introduce a desirable phenotype to the host cell through the proteins, nucleic acids or other factors that are secreted into the host cell from the artificial endosymbiont.
In some embodiments, the proteins, nucleic acids, or other factors secreted from an artificial endosymbiont into the host cell can be used to affect cell viability, proliferation, differentiation, de-differentiation, growth, angiogenesis, neurogenesis, osteogenesis, and detoxification. In some embodiments, the artificial endosymbiont can be used to label the cell, treat a pathology or deficiency, induce cell death, induce wound healing, modify cell signaling, modify gene expression, neutralize intracellular proteins or nucleic acids, or provide metabolic pathways for creating biofuels or new energy sources. In some embodiments, the artificial endosymbiont is used to modify cell function by providing, among others, nutrients, growth factors, proteins, minerals, nucleic acids, therapeutic agents, small molecules, ions, chemokines, polysaccharides, lipids, metals, cofactors, and hormones. In some embodiments, the artificial endosymbiont may also be used to manufacture with the host cell bioremediation agents, enzymes, neurotransmitters, polypeptides, carbohydrates, pesticides, fertilizers, and other desirable compounds. In some embodiments, an endosymbiont can secrete proteins related to energy generation or exchange, such as hydrogenase, nitrogenase, and laccase.
In some embodiments, the artificial endosymbiont can secret an amino acid into the host cell, including, alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, or valine.
In some embodiments, the artificial endosymbiont can secrete into a host cell a nucleic acid, RNA, mRNA, hnRNA, ShRNA, siRNA, microRNA, antisense RNA or DNA, or DNA. Genetic material exchange between an artificial endosymbiont and a host cell can be used for gene therapy, to silence a gene, to transcribe a gene, to replace a gene, to modify expression of a gene, to modify a gene, to introduce a gene or nucleic acid fragment, to bind nucleic acids, or to interact with nucleic acids.
In some embodiments, the artificial endosymbiont can introduce into the host cell signal pathway molecules, such as, for example, receptors, ligands (hormones, neurotransmitters, cytokines, chemokines), ion channels, kinases, phosphatases, DNA bindings proteins (e.g., transcription factors, repressors, enhancers), and the like. An exemplary set of proteins for reprogramming cells are the Yamanaka factors, which include Oct4, Oct3, Sox2, Klf4, c-Myc, NANOG, and Lin28. Expression of all or a subset of the Yamanaka factors can reprogram mature cells into iPS cells (see, e.g., Takahashi et al., “Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors,” Cell 131(5):861-72, 2007).
In some embodiments, an artificial endosymbiont can be used to sense intracellular moieties to quantify intracellular levels of such moiety, drive release of an agent, drive cell death, drive expression of a gene, label the cell, or sense cell viability, differentiation, or cell cycle stage.
In some embodiments, an artificial endosymbiont can secrete transcription factors used to reprogram a cell, for example Oct4. In some embodiments, an artificial endosymbiont can secrete an enzyme to replace enzyme deficiencies, for example, in a lysosomal storage disease or ALDH2. In some embodiments, an artificial endosymbiont can secrete a moiety to label a cell, such as Calcein, superparamagnetic iron oxide, gadolinium containing reagents, fluorescent proteins, luminescent proteins, magnetic reporters, other reporter proteins (Gilad et al., “MRI Reporter Genes,” J Nucl Med. 49:1905-08, 2008; incorporated herein by reference). In some embodiments, the artificial endosymbiont can secrete a protein or other factor that provide a beacon for the host cell from a reporter, such as a fluorescent protein (e.g., GFP, RFP, YFP, CFP, etc.), and/or luciferase. Other reporters that can be secreted include, among others, enzymes, epitope tags, and heterologous proteins not normally expressed in the host cell.
Prokaryotes have evolved to survive in many ecological niches and thus have a staggeringly large biodiversity. Conversely, eukaryotes have a much more limited biochemistry but have the ability to create complex structures, tissues and organisms. Thus, in some embodiments, the present invention is used to integrate the biodiversity of prokaryotes into the organismal complexity of eukaryotes. This capability relies on the ability of the artificial endosymbiont and host cell to communicate or transfer various substances or signals from one to the other and vise versa. Specific problems encountered by host cells that are solved by artificial endosymbionts can create a number of new host cells. For example, issues in plant agriculture today include, among others, use of fertilizers; shrinking fresh water supplies; temperature and climate fluctuations; insect, pest and fungal infections; toxic soil environments and diminishing nutritional value. These are all issues that bacteria have solved.
An example of an application of the present invention is providing a source of fixed nitrogen, which is the main component of fertilizers, for the growth of plants and fungi. There is a large and diverse class of microbes that fix atmospheric nitrogen using the enzyme nitrogenase. These include, among others, Anabaena, Nostoc, Diazotroph, Cyanobacteria, e.g. the highly significant Trichodesmium, Beijerinckia, Clostridium, Green sulfur bacteria, Azotobacteraceae, Rhizobia, and Frankia. Thus, in some embodiments, artificial endosymbionts derived from such organisms can be used to fix nitrogen from the air and transport a nitrogen containing compound compatible with the host cell's metabolism.
Another application of the present invention is to address concerns regarding fresh water supplies, which could in principle be alleviated if crop plants could be irrigated or grown hydroponically with seawater. This would create a large osmotic stress on the plant cells. Surviving high salt environments is an ecological niche in which halophilic bacteria thrive, including members from flavobacteria, cyanobacteria, proteobacteria, firmicutes, methanosarcinales and halobacteriales. Generally two types of osmotic adaptation have been reported: accumulation of inorganic ions or synthesis of organic osmotic solutes. The former “high-salt in” strategy provided by artificial endosymbionts could reduce the osmotic stress on plant cells, allowing the crop to survive seawater irrigation by concentrating salt ions into the artificial endosymbiont, thus lowering the host cell cytoplasmic salt levels below lethal. This strategy is used by the aerobic halophilic Archaea of the order Halobacteriales, the fermentative anaerobes of the order Halanaerobiales (low G+C brand of the Firmicutes) and the red aerobic Salinibacter (Bacteroidetes branch).
In some embodiments, artificial endosymbionts can be used to impart molecular and physiological adaptations, such as tolerability to extreme environments. For example, thermophilic and psychrophilic microbes have colonized temperature and climate extreme environments. Thermophiles have evolved their proteins, membranes and cellular components to withstand temperatures, in the most extreme cases, above 100° C. Artificial endosymbionts could extend the temperature range available to some crops. Artificial endosymbionts derived from psychrophiles or psychrotrophs, may provide cold resistance to plants and fungi. These microorganisms have a range of molecular and physiological adaptations: cold adapted enzymes, unique lipids for membranes that maintain fluidity at lower temperatures, cryoprotectants such as exopolysaccharides and cold shock or antifreeze proteins. The secretion of cryoprotectants into host cells would provide a cold tolerant phenotype. Genera of such bacteria include, among others, Marinobacter, Halomonas, Dermacoccus, Kocuria, Micromonospora, Streptomyces, Williamsia, Tskamurella, Clostridium, Alteromonas, Colwellia, Glaciecola, Pseudoalteromonas, Shewanella, Polaribacter, Pseudomonas, Psychrobacter, Athrobacter, Frigoribacterium, Subtercola, Microbacterium, Rhodoccus and Bacillus. The genomes of a number of these have or are being sequenced: M. frigidum, M. burtonii, C. symbiosum, C. psychrerythraea, P. haloplanktis, Halorubrum lacusprofundi, Vibrio salmonicida, Photobacterium profundum, S. violacea, S. frigidimarina, Psychrobacter sp. 273-4, S. benthica, Psychromonas sp. CNPT3, Moritella sp., Desulfotalea psychrophila, Exiguobacterium 255-15, Flavobacterium psychrophilum, Psychroflexus torquis, Polaribacter filamentous, P. irgensii, Renibacterium salmoninarum and Leifsonia-related PHSC20-c1.
In some embodiments, artificial endosymbionts are used as remedial measures against pollution and other toxic components in the environment. For example, soil environments can become unsuitable for agriculture due to the presence of toxic levels of heavy metals or other pollutants. Artificial endosymbionts that metabolize these or concentrate them and thus provide a resistant phenotype to the host plant. Classes of microorganisms known as Acidophiles have the ability to tolerate high concentrations of metals (e.g., arsenic, mercury, copper, iron, etc.) and metalloids. The genomes of Acidithiobacillus ferrooxidans, Thermoplasma acidophilum, Picrophilus torridus, Sulfolobus tokodaii and Ferroplasma acidarmanus have been sequenced, and such organisms can be introduced into host cells to provide tolerance against such toxic environments.
In some embodiments, artificial endosymbionts can be used to produce and deliver essential vitamins, for example, B12, biotin, folic acid, and pantothenate to host cells. Such nutrients are synthesized by several intestinal genera of bacteria, including Bacteroides, Eubacterium, Propionibacterium, and Fusobacterium (Hooper, L. V. et al., “How host-microbial interactions shape the nutrient environment of the mammalian intestine,” Annu Rev Nutr. 22:283-307, 2002). Pseudomonas, Klebsiella, lecithinase-positive Clostridia, Veillonella and Fusobacteria produce considerable amounts of Vitamin B12 like material (Albert, M. J. et al., “Vitamin B12 synthesis by human small intestinal bacteria,” Nature 283:781-82, 1980; incorporated herein by reference).
In some embodiments, the present invention can be used in synthetic biology applications. Over the past decades, advances in genetics, synthetic biology and microbiology have created a large number of engineered microbes for various bioindustrial, biopharmaceutical, and other commercial applications. A limitation of these systems is that the engineered microbe needs to support the genetics and metabolism for both cell viability (e.g., housekeeping functions) and function of the engineered pathways. Artificial endosymbionts provide an alternative strategy because the housekeeping functions are provided by the host, which allows more resources to be dedicated to the engineered functionality in the artificial endosymbiont. In a medical setting, drug eluting artificial endosymbionts could replace cellular functions underlying numerous diseases; returning insulin production to pancreatic cells, restoring hormone or metabolic deficiencies, etc. In an industrial setting, artificial endosymbionts could increase the yields of numerous biosynthesized materials, biofuels, etc.
In some embodiments, artificial endosymbionts that provide carbon, energy (like the endosymbiotically derived mitochondria, hydrogensomes, plastids, mitosomes and mitochondrion-derived organelles) or other metabolites could be useful commercially, for example, enabling animal cells to derive carbon and/or ATP though the Calvin cycle and photosynthesis, thereby allowing use of in-lab grown food stocks. Attempts to transfer chloroplast from plant cells to animal cells have been reported previously (Bonnett, H. T., “On the mechanism of the uptake of Vaucheria; chloroplasts by carrot protoplasts treated with polyethylene glycol,” Planta 131:229-33, 1976; Giles, K. et al., “Liposome-mediated uptake of chloroplasts by plant protoplasts,” In Vitro Cellular & Developmental Biology—Plant 16:581-4, 1980; incorporated herein by reference). Since the majority of the chloroplasts proteins are encoded in the nuclear genome it is not surprising that these have yet to be successful. Indeed the definition of an endosymbiotically-derived organelle is transfer of genetic material to the host nuclear genome.
In some embodiments, ATP production using an electron donor other than oxygen could be used to enable various host cells to inhabit new niches, potentially even extraterrestrial. Microorganisms have many ways to produce ATP: phototrophy, chemotrophy, photolithotrophy (examples: cyanobacteria, Chromatiaceae, Chlorobiceae), photoorganotrophy (example Rhodospirillaceae), chemolithotrophy (examples: hydrogen-oxidizing bacteria, thiobacilli, nitrosomonas, nitrobacter, methanogens, acetogens) and chemoorganotrophy (examples: pseudomonads, bacillus, sulfate reducers, clostridia, lactic acid bacteria), and artificial endosymbionts containing such metabolic pathway or artificial endosymbionts engineered to contain such pathways can be introduced into appropriate host cells.
Recently bacteria that produce or conduct electricity have been described. Artificial endosymbionts derived from these bacteria could enable complex tissues to be created that have the ability to interact directly with electronics.
The invention will be better understood from the experimental details which follow. However, one skilled in the art will readily appreciate that the specific methods and results discussed are merely illustrative of the invention as described, and therefore are not intended to be exhaustive or to limit the invention to the precise forms disclosed.
EXAMPLES
Example 1
Translocation of Proteins into Host Cells Using a Type I Secretion System from an Artificial Endosymbiont
The type I secretion systems (T1SS) in Gram-negative bacteria can be used to export a variety of proteins of various sizes and diverse functions (their cognate substrates). The MTB genome encodes T1SS genes (Matsunga, T. et al., “Complete genome sequence of the facultative anaerobic magnetotactic bacterium Magnetospirillum sp. AMB-1,” DNA Res. 12:157-66, 2005; incorporated herein by reference in its entirety).
Target protein, green fluorescent protein (GFP), or red fluorescent protein (RFP), is N-terminally fused to C-terminal 200 amino acids of YP_420640 (RTX toxins and related Ca2+ binding protein), YP_423419 (RTX toxins and related Ca2+ binding protein), YP_422785 (amb3422), or other MTB T1SS substrates. Alternatively, the proteins in MTB-YP_420502, YP_420631.1, YP_420638.1, YP_420640.1, YP_421364.1, YP_422662.1, YP_422785.1, and YP_423419.1 can be used for the fusion by taking their C-terminus (e.g., the 200 C-terminal amino acids which contains the secretion signal) to target the recombinant fusion protein to the secretion system. The DNA encoding the fusion of GFP or RFP with 200 C-terminal amino acids of YP_420640 (RTX toxins and related Ca2+ binding protein), YP_423419 (RTX toxins and related Ca2+ binding protein), YP_422785 (amb3422), or other MTB T1SS substrates is cloned into pBBR-MSC (Kovach, M. E. et al, pBBR1MCS: a broad-host-range cloning vector,” Biotechniques 16:800-2, 1994). Translocation of the fusion protein out of the artificial endosymbiont is detected by fluorescence, or immunofluorescence and/or immunoblotting.
In another specific example, the hemolysin (Hly) secretion system of E. coli is one of the best studied type I secretion systems (T1SS). Secretion of the hemolysin A toxin (HlyA) is catalyzed by a membrane protein complex (Bakkes, P. J., et al., “The rate of folding dictates substrate secretion by the Escherichia coli hemolysin type 1 secretion system,” J Biol Chem. 285(52):40573-80, 2010) that consists of HlyB, an inner membrane protein that is an ATP binding cassette transporter (Davidson, A. L. and J. Chen “ATP-binding cassette transporters in bacteria,” Annu Rev Biochem. 73:241-68, 2004), TolC, the outer membrane protein (Koronakis, V., et al. “Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export,” Nature 405(6789):914-9, 2000), and HlyD, the membrane fusion protein that is anchored to the inner membrane (Johnson, J. M. and G. M. Church, “Alignment and structure prediction of divergent protein families periplasmic and outer membrane proteins of bacterial efflux pumps,” J Mol Biol. 287(3):695-715, 1999). Export of HlyA requires ATP hydrolysis by HlyB (Thanabalu, T., et al., “Substrate-induced assembly of a contiguous channel for protein export from E. coli: reversible bridging of an inner-membrane translocase to an outer membrane exit pore,” EMBO J. 17(22):6487-96, 1998). The last 218 C-terminal amino acids of HlyA have been shown to direct the secretion of a large variety of polypeptides through the T1SS (Kenny, B. et al., “Analysis of the haemolysin transport process through the secretion from Escherichia coli of PCM, CAT or beta-galactosidase fused to the Hly C-terminal signal domain,” Mol Microbiol. 5:2557-68, 1991; Mackman, N. et al., “Release of a chimeric protein into the medium from Escherichia coli using the C-terminal secretion signal of haemolysin,” EMBO J. 6, 2835-41, 1987; Holland, I. B., et al., “The mechanism of secretion of hemolysin and other polypeptides from gram-negative bacteria,” J Bioenerg Biomembr. 22(3):473-91, 1990).
In order to translocate a protein, such as GFP or RFP, out of the bacterial cell into a target host cell via the T1SS, the protein, GFP, for example (GenBank: ABG78037.1) will be fused to the last 218 C-terminal amino acids of HlyA (HlyAN-term 218, UniProtKB/Swiss-Prot: P09983.1, bolded-underlined sequence):







(SEQ ID NO: 298)


MVSKGEELFTGVVPILVELDGDVNGHKFSVSGEGEGDATYGKLTLKFIC


 


TTGKLPVPWPTLVTILTYGVQCFSRYPDHMKQHDFFKSAMPEGYVQERT


 


IFFKDDGNYKTRAEVKFEGDTLVNRIELKGIDFKEDGNILGHKLEYNYN


 


SHNVYIMADKQKNGIKVNFKIRHNIEDGSVQLADHYQQNTPIGDGPVLL


 


PDNHYLSTQSALSKDPNEKRDHMVLLEFVTAAGITLGMDELYKGNSLAK


 


NVLSGGKGNDKLYGSEGADLLDGGEGNDLLKGGYGNDIYRYLSGYGHHI


 


IDDDGGKDDKLSLADIDERDVAFRREGNDLIMYKAEGNVLSIGHKNGIT


 


EKNWEEKESGDISNHQIEQIFDKDGRVITPDSLKKALEYQQSNNKASYV


 


YGNDALAYGSQGNLNPLINEISKIISAAGNFDVKEERAAASLLQLSGNA


 


SDFSYGRNSITLTASA






For, example, the GFP-HlyAC-term 218 fusion will be secreted out of the bacterial cell into the host cell via the HlyB-HlyD-TolC complex. The GFP-HlyAC-term 218 fusion as well as the HlyB-HlyD-TolC complex will be engineered into the pBBR1MCS-2 plasmid and be expressed under the control of the tac promoter. Translocation of the GFP-HlyAC-term 218 fusion into target host cells will be monitored by fluorescence microscopy.
Translocation/Secretion assays (to demonstrate that proteins are secreted from MTB). Dilute (1:10) overnight cultures of MTB strains harboring the appropriate recombinant plasmids into fresh MG supplemented with antibiotics (for culture conditions, see Greene, S. E. et al., “Analysis of the CtrA pathway in Magnetospirillum reveals an ancestral role in motility in alpha proteobacteria,” J Bact. 194:2973-86, 2012). Cells carrying the defined plasmid combinations are grown to an optical density of 400 nm (OD400) of 0.2 before IPTG or arabinose is added to induce the expression of target protein fusions. Proteins in the supernatants are precipitated with 10-20% trichloroacetic acid for 30 min at 4° C. The precipitated proteins are collected by centrifugation and washed in 80% acetone. Cell pellets are washed once in 20 mM Tris (pH 8.0)-1 mM EDTA. Cell pellets and precipitated supernatants are resuspended in 1× sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) loading buffer and amounts equivalent to 0.2 OD unit are analyzed by SDS-PAGE and immunoblotting. Proteins are stained with Coomassie Brilliant Blue and/or probed by immunoblotting using specific antibodies. MTB isolates that secrete GFP are introduced to the mammalian cell line MDA-MB231, using the magnet assisted entry method. Cells with artificial endosymbionts are obtained, and translocated protein is detected by fluorescence, or immunofluorescence or immunoblotting.
Example 2
Translocation of a Protein into a Host Cell Using a Type IV Secretion System from an Artificial Endosymbiont
CagA is secreted through a T4SS system by engineering a CagA protein by replacing the last 20 amino acids with 24 amino acids (residues 684-709) from the C-terminal end of the RSF1010 MobA protein. Translocation of CagA-MobA into the host cell is monitored by observation of the hummingbird phenotype caused by CagA in the host cell. The hummingbird phenotype is described in Segal et al. as “characterized by spreading and elongated growth of the cell, the presence of lamellipodia (thin actin sheets present at the edge of the cell), and filapodia (finger-like protrusions containing a tight bundle of actin filaments (see Segal, E. D. et al., “Altered States: Involvement of Phosphorylated Caga in the Induction of Host Cellular Growth Changes by Helicobacter Pylori,” Proc Natl Acad Sci. USA 96(25):14559-64, 1999)
The hummingbird phenotype resembles the morphological changes induced by hepatocyte growth factor (HGF) or platelet-derived growth factor (PDGF) in epithelial cells (Sugiyama, T., “Development of gastric cancer associated with Helicobacter pylori infection,” Cancer Chemother Pharmacol. 54(Suppl 1):S12-20, 2004). Hepatocyte growth factor, also known as scatter factor, evokes a unique morphogenic activity, e.g., induces kidney, or mammary gland-derived epithelial cells, to form branching ducts in three-dimensional collagen gels (Ohmichi, H. et al., “Hepatocyte growth factor (HGF) acts as a mesenchyme-derived morphogenic factor during fetal lung development,” Development 125:1315-1324, 1998).
Other proteins, including GFP, are fused to the C-terminal residues of MobA (see sequence below) in order to be translocated from Helicobacter pylori with a T4SS into a MDM-MB231 host cell. In the case of GFP, translocation of this protein into the MDM-MB231 host cell can be monitored by looking for the presence of GFP fluorescence outside of the artificial endosymbiont.
GFP amino acid sequence (GenBank: ABG78037.1, sequence) fused to MobA residues 684-709 (GenBank: AAA26445.1, bolded-underlined sequence) is shown below:







(SEQ ID NO: 299)


MVSKGEELFTGVVPILVELDGDVNGHKFSVSGEGEGDATYGKLTLKFIC


 


TIGKLPVPWPTLVTILTYGVQCFSRYPDHMKQHDFFKSAMPEGYVQERT


 


IFFKDDGNYKTRAEVKFEGDTLVNRIELKGIDFKEDGNILGHKLEYNYN


 


SHNVYIMADKQKNGIKVNFKIRHNIEDGSVQLADHYQQNTPIGDGPVLL


 


PDNHYLSTQSALSKDPNEKRDHMVLLEFVTAAGITLGMDELYKLARAEL


 


ARAPAPRQRGMDRGGPDFSM.






Alternatively, other proteins, including GFP, could be fused to the C-terminal 50 amino acid residues of VirD5 in order to be translocated from A. tumefaciens via a T4SS into a MDM-MB231 host cell. In the case of GFP, translocation of this protein into the MDM-MB231 host cell can be monitored by looking for the presence of GFP fluorescence.
GFP amino acid sequence (GenBank: ABG78037.1, sequence) fused to VirD5 residues 787-836 (NCBI Reference Sequence: YP_001967549.1, bolded-underlined sequence) is shown below:







(SEQ ID NO: 300)


MVSKGEELFTGVVPILVELDGDVNGHKFSVSGEGEGDATYGKLTLKFIC


 


TIGKLPVPWPTLVTILTYGVQCFSRYPDHMKQHDFFKSAMPEGYVQERT


 


IFFKDDGNYKTRAEVKFEGDTLVNRIELKGIDFKEDGNILGHKLEYNYN


 


SHNVYIMADKQKNGIKVNFKIRHNIEDGSVQLADHYQQNTPIGDGPVLL


 


PDNHYLSTQSALSKDPNEKRDHMVLLEFVTAAGITLGMDELYKISALDR


 


TARLISISPSKARSKAETEKAIDELDDRRVYDPRDRAQDKAFKR.






Example 3
Translocation of a Nucleic Acid into a Host Cell Using a Type IV Secretion System from an Artificial Endosymbiont
CagA The type 4 secretion system (T4SS) can be used to transfer plasmid DNA from an artificial endosymbiont into a mammalian host cell. Sequence analysis reveals that components of the T4SS system are present in MTB.
Plasmid pBBR-MSC is engineered to include (oriT+trwABC) for transfer of the plasmid by a T4SS system, and the plasmid is engineered to contain an expression cassette encoding the target protein under control of the HCMV IE1 promoter-enhancer-first intron. The target protein is a selectable marker such as DHFR or glutamate synthetase, or a reporter such as GFP, or a transcription factor such as cMyc.
A mammalian selectable marker can be used as the target gene. These include puromycin N-acetyl-transferase gene for puromycin resistance; blasticidin S deaminase for blasticidin S resistance; and aminoglycoside 3′-phosphotransferase for G418 resistance. If MDA-MB231 is used as a host cell line, 2 ug/ml puromycin, 5 ug/ml blasticidin S, or 1 mg/ml G418 is used for selection.
Plasmid DNA harboring a DNA fragment of interest along with an antibiotic resistance cassette (the choice of cassette will vary depending on the conditions needed) can be introduced into MTB via conjugation with a mating strain of E. coli that is auxotrophic to diaminopimelic acid (DAP). Successful transfer of the plasmid DNA to MTB will result in growth of MTB on MG agar plates in the presence of antibiotic. The E. coli mating strain auxotrophic to (DAP) will ensure that any growth seen on the MG agar plates+antibiotic will be strictly MTB as no E. coli colonies should survive on plates not containing DAP. MTB colonies harboring the plasmid DNA will be cultured in liquid MG growth medium to be used in subsequent experiments where MTB will be introduced into mammalian cells. MTB with the plasmid are introduced into mammalian cells, such as the human breast cancer cell line MDA-MB231. The plasmid will then integrate into the host cell chromosome via non-homologous recombination. Transfer of plasmid nucleic acid from MTB, the artificial endosymbiont, to the host cell (MDA-MB231) is detected by selection for host cells that grow in the presence of 2 ug/ml puromycin, 5 ug/ml blasticidin S, or 1 mg/ml G418. Selected cells are grown and then suitable assays are performed to detect chromosomal integration of the plasmid into the host cell genome, such as for example, in situ hybridizations or Southerns.
Example 4
Transport of Reporter Protein into a Eukaryotic Host Cell
Reporter protein transport construct. A 600 base pair polynucleotide encoding the transport sequence denoted as 422785 (from YP_422785), which is the 200 amino acid (SEQ ID NO:291) C-terminal end of protein amb3422 (accession no. YP_422785), a putative Type 1 Secretion System (T1SS) protein native to Magnetospirillum magneticum AMB-1, was fused to a polynucleotide encoding a GFP without a stop codon, referred to as GFPmut3 gene. The polynucleotide encoding the fusion protein was operably linked to the lac promoter and the fusion protein expressed using the extrachromosomal plasmid pBBR1MCS-2. This construct was sequence validated and conjugated into M. magneticum AMB-1 to create M. magneticum AMB-1 strain AC16.
Measuring green fluorescence of bacterial cells and extracellular supernatant. M. magneticum AMB-1 strain AC16 and non-fluorescent M. magneticum AMB-1 were grown in standard media (see, e.g., US patent publication US2013/0183758). Green fluorescence of M. magneticum AMB-1 strain AC16, non-fluorescent M. magneticum AMB-1, and their respective aliquots of extracellular supernatant were measured using a BioTek® Synergy H1 Microplate Reader with excitation wavelength of 485/20 nm and emission wavelength of 528/20 nm. Both M. magneticum AMB-1 strains assessed were adjusted to optical density at wavelength of 400 nm (OD400) of 0.195 to ensure all samples contained the same amount of bacterial cells per unit volume. To assess the presence of green fluorescent protein (GFP) that has been transported out from M. magneticum AMB-1 and into the extracellular space, 1 ml aliquots of supernatant from each M. magneticum AMB-1 strain with no cells present were obtained via centrifugation at 13,000 rpm for 10 min. Without disturbing the bacterial pellet, 200 μl of the supernatant were pipetted out and dispensed into wells of a black 96-well microplate. In parallel, 200 μl of M. magneticum AMB-1 cells in suspension of each strain were dispensed into wells of the microplate in order to assess total green fluorescence from both intracellular and extracellular GFP. This experiment was done in biological and technical triplicates. Measurements of GFP fluorescence in supernatants of AC16 and AMB-1 (negative control) are shown in FIG. 10. Results show that there were significantly higher levels of green fluorescence in the extracellular supernatant of AC16 as compared to that of the M. magneticum AMB-1 negative control (denoted as AMB-1 Neg Ctrl). Comparison of fluorescence levels in supernatant of AC16 cells and cells in suspension are shown in FIG. 11. Results show that there was no significant difference between levels of green fluorescence detected in the supernatant of AC16 cells and that detected with AC16 cells in suspension, which indicates that the majority of GFP signal is from the extracellular medium. There is no significant difference between green fluorescence detected in the supernatant of the AMB-1 Neg Ctrl and that detected with the same bacterial cells in suspension, which suggests that this low fluorescence is due to background.
Immunohistochemisty to detect translocation of GFP. To examine the translocation of fusion protein (GFP fused to C-terminal 200 amino acids of YP_422785) from magnetotoactic bacteria Magnetospirillum magneticum AMB-1 to eukaryotic cells (human breast cancer cells MDA-MB231), MDA-MB231 cells were grown in standard cell culture medium (e.g., DMEM media supplemented with 10% fetal calf serum) and the cells labeled with M. magneticum AMB-1 strain AC16, for example by mixing AC16 cells with MDA-MB231 cells and then using a NdFeB, Grade N52 magnet to assist in introduction of the M. magneticum AMB-1 cells into the MDA-MB231 cells. The transfer of the fusion protein from magnetotactic bacteria into the extracellular environment was monitored by immunofluorescence microscopy. Briefly, MDA-MB231 cells were labeled with magnetotactic bacteria, and at various time points post-labeling the labeled MDA-MB231 cells were fixed in 4% paraformaldehyde, permeabilized and blocked with 0.1% Triton X-100 and 1% bovine serum albumin. Eukaryotic cells were stained with GFP and AMB-1 antibodies for 1 h at room temperature. Slides were washed and incubated with Alexa Fluor 488 donkey anti-rabbit and Alexa Fluor 594 donkey anti-mouse IgG (H+L) secondary antibodies for 30 min. Slides were washed and mounted with Vectashield with DAPI, and fluorescence images were obtained using fluorescence microscope.
FIG. 12 shows fluorescence microscopy images (40×) of MDA-MB231 cells labeled with AMB-1 containing (A) only GFP plasmid and (B) GFP-fused to C-terminal 200 amino acids of YP_422785, one day after labeling with the M. magneticum AMB-1 cells and dually stained with the antibodies. Both panels are merged images of anti-GFP (red), anti-AMB-1 (green), and DAPI (blue). The translocation of GFP-fusion protein (in panel B) to the extracellular environment is revealed by double immunoflourescent staining of AMB-1 labeled MDA-MB231 cells, demonstrating the ability of AMB-1 to transfer proteins into the host cells using type 1 secretion system.
FIG. 13. shows fluorescence microscopy of AMB-1 labeled MDA-MB231 cells (single channel and composite images) (40× images). MDA-MB231 cells were labeled with AMB-1 containing GFP plasmid only (without the secretion sequence), and the cells dually stained one day post-labeling and examined by fluorescence microscopy: (A) AMB-1 only (green channel), (B) GFP (red channel), (C) DAPI (blue channel), and (D) merged images of AMB-1 (green channel), GFP (red channel), and DAPI (blue channel) The translocation of GFP protein (in Panel B) to the extracellular environment was not observed by double immunoflourescent staining of MDA-MB231 cells containing AMB-1 cells containing GFP only.
FIG. 14 shows fluorescence microscopy of MDA-MB231 cells labeled with AC16 cells (single channel and composite images) (40× images). MDA-MB231 cells were labeled with AC16 cells (AMB-1 containing GFP-fused to C-terminal 200 amino acids of YP_422785) and dually stained one day post-labeling and examined by fluorescence microscopy: (A) AMB-1 (green channel), (B) GFP (red channel), (C) DAPI (blue channel), and (D) merged images of AMB-1 (green channel), GFP (red channel), and DAPI (blue channel) The translocation of GFP-fusion protein (in Panel B) to the extracellular environment is revealed by double immunoflourescent staining of AMB-1 labeled MDA-MB231 cells, demonstrating the ability of AMB-1 to transfer proteins into the host cells using type 1 secretion system.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching.
All patents, patent applications, publications, and references cited herein are expressly incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

## Claims

1. An isolated mammalian cell comprising a magnetotactic bacterium, wherein the magnetotactic bacterium provides a protein to the host cell and thereby provides a phenotype to the mammalian cell.

2. The mammalian cell of claim 1, wherein the mammalian cell is a stem cell.

3. The mammalian cell of claim 2, wherein the stem cell is a neural stem cell.

4. The mammalian cell of claim 2, wherein the stem cell is a mesenchymal stem cell.

5. The mammalian cell of claim 2, wherein the stem cell is a neural crest stem cell.

6. The mammalian cell of claim 1, wherein the mammalian cell is a neural progenitor cell.

7. The mammalian cell of claim 1, wherein the mammalian cell is selected from the group consisting of a murine cell, a rat cell, a rabbit cell, a hamster cell, a porcine cell, a bovine cell, a feline cell, a canine cell and a human cell.

8. The mammalian cell of claim 7, wherein the mammalian cell is a human cell.

9. The mammalian cell of claim 7, wherein the mammalian cell is a murine cell.

10. The mammalian cell of claim 1, wherein the protein is a magnetosome protein.

11. A method for introducing a phenotype into a mammalian cell, comprising the steps of: culturing an isolated mammalian cell comprising a magnetotactic bacterium, expressing a protein in the magnetotactic bacterium, secreting the protein from the magnetotactic bacterium to the mammalian cell whereby the protein produces a phenotype in the mammalian cell.

12. The method of claim 11, wherein the protein is a selectable marker.

13. The method of claim 11, wherein the protein is a reporter protein.

14. The method of claim 13, wherein the protein is a magnetosome protein.

15. The method of claim 11, wherein the mammalian cell is stem cell.

16. The method of claim 15, wherein the stem cell is a neural stem cell.

17. The method of claim 15, wherein the stem cell is a mesenchymal stem cell.

18. The method of claim 17, wherein the stem cell is a neural crest stem cell.

19. The method of claim 11, wherein the mammalian cell is a neural progenitor cell.

20. The method of claim 11, wherein the mammalian cell is selected from group consisting of a murine cell, a rat cell, a rabbit cell, a hamster cell, a porcine cell, bovine, a feline cell, a canine cell and a human cell.