Type VI secretion systems (T6SS) enable bacteria to engage neighboring cells in contact-dependent competition. In Vibrio cholerae, three chromosomal clusters each encode a pair of effector and immunity genes downstream of those encoding the T6SS structural machinery for effector delivery.

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Different combinations of effector-immunity proteins lead to competition between strains of V. Cholerae, which are thought to be protected only from the toxicity of their own effectors. Screening of all publically available V. Cholerae genomes showed that numerous strains possess long arrays of orphan immunity genes encoded in the 3′ region of their T6SS clusters.

Parov Stelar The Invisible Girl Album Download. Phylogenetic analysis reveals that these genes are highly similar to those found in the effector-immunity pairs of other strains, indicating acquisition by horizontal gene transfer. Extensive genomic comparisons also suggest that successive addition of effector-immunity gene pairs replaces ancestral effectors, yet retains the cognate immunity genes. The retention of old immunity genes perhaps provides protection against nearby kin bacteria in which the old effector was not replaced. This mechanism, combined with frequent homologous recombination, is likely responsible for the high diversity of T6SS effector-immunity gene profiles observed for V. Cholerae and closely related species.

The family Vibrionaceae consists of over 100 related species of highly motile, heterotrophic bacteria that enzymatically convert inaccessible organic matter found in aquatic environments into carbon sources available to higher trophic levels of the ecosystem they inhabit. Numerous mostly harmless lineages of Vibrio coexist within niches, competing for largely similar resources. Among them are a few human pathogens of relevance, including Vibrio cholerae, the causative agent of the sometimes dramatic and lethal cholera diarrhea. More specifically, a single lineage of the V.

Cholerae species, comprised primarily of O1 and O139 serogroup strains, has adapted to effectively colonize the human gastrointestinal tract and is responsible for all known cholera pandemics. Cholerae strains harbor the horizontally acquired genetic elements VPI-1 and CTX-Φ, encoding the toxin co-regulated pilus and cholera toxin respectively. These virulence factors enable pandemic strains to colonize the crypts of villi in the small intestine, causing watery purges of diarrhea and releasing billions of pathogenic bacteria into the environment. Thus, pathogenic V.

Cholerae lead a dual lifestyle: One that requires the ability to pursue, attach and colonize biotic surfaces in a relatively oligotrophic aquatic environment of low osmolarity, and another that requires the successful colonization of a eutrophic, biochemically challenging human intestine populated by a highly diverse commensal host flora. Software Alat Musik. In both of these competitive environments, V. Cholerae is believed to actively employ their Type VI secretion system (T6SS), which is induced by chitin in the environment and by bile salts in the gut.

The T6SS is a membrane-spanning nanomachine capable of injecting toxin-tipped protein spears into adjacent eukaryotic and bacterial target cells. The T6SS spear consists of Hcp multimers tipped by a VgrG (hetero)trimer and effector proteins with varying cytotoxic effects. For example, the VgrG-1 protein of some V. Cholerae strains harbors a C-terminal domain that mediates crosslinking of cytoskeletal actin fibers in eukaryotic cells (such as predatory amoebae or macrophages), leading to cell rounding and death.

VgrG-3, on the other hand, displays antibacterial properties by degrading prokaryotic peptidoglycan, and is also an important factor in the colonization of the human intestine. Additionally, so-called cargo effectors can be loaded onto the Hcp-VgrG spear, further expanding the toxic capabilities of the T6SS.

Unterweger et al. Found that a multitude of diverse T6SS effector-immunity (EI) gene modules are encoded in different V.

Cholerae genomes. Effector proteins are placed as cargo onto the T6SS-spear by an adaptor protein, while immunity proteins remain inside the cell and prevent intoxication by incoming cognate effectors.

The resulting “poisoned” spear proves lethal to target cells that do not possess an EI module of the same type. Through this system, strains of V.

Cholerae are not only able to attack eukaryotes and bacteria belonging to different species, but also their perhaps strongest competitors, non-kin strains of the same species. Unterweger et al. Established a three-letter system for typing V. Cholerae T6SS variants based on their EI modules. Different letters designate unique EI gene families (as defined by a 30% amino acid identity of immunity proteins) encoded in three genomic clusters: aux-1 (A and C), aux-2 (A-E) and the large cluster (A-G). In the case of the large cluster, the effector is a domain at the 3′ end of vgrG-3, not a separate gene ().