A Genomic Island in Vibrio cholerae with CRISPR-Cas and T6SS Regions

Yan, Fabini, and Paul collaborated with Dr. Maurizio Labbate (University Technology Sydney) and published a paper in Scientific Reports about a ~28-kb genomic island (GI; designated as GIVchS12) in a non-O1/O139 strain of Vibrio cholerae located in the same position where the Vibrio Pathogenicity Island - 1 (VPI-1) would be as it has VPI-1 site-specific recombination characteristics. VPI-1, which has so far only been found in some O1 and O139 V. cholerae strains (with pathogenic strains causing cholera epidemics and pandemics), contains the toxin-coregulated pilus (tcp) cluster. TCP is a precursor for infection of V. cholerae by the CTX phage (that contains the cholera toxin) as it serves as receptor for the phage. It is also important for the colonization of the small intestine during V. cholerae infection of the host. On the other hand, GIVchS12 does not contain the same genes as VPI-1. It contains CRISPR-Cas and type VI secretion system (T6SS) modules. CRISPR-Cas is a defense mechanism by bacteria against unwanted lateral gene transfer by recognizing foreign DNA and cleaving it. T6SS is for inter-cell anatgonism, where T6SS-harbouring bacteria produce a membrane-spanning protein complex used to puncture and kill nearby eukaryotic or prokaryotic cells.

Our survey of representative V. cholerae genomes suggests the presence of genomic islands similar to GIVchS12 containing CRISPR-Cas and T6SS modules from various strains. Natural populations of V. cholerae can serve as reservoir for diverse GIs such as GIVchS12.

Schematic representation of V. cholerae S12 genomic island GIVchS12 (from Labbate et al., 2016)