Distribution and variation of VSP-Ⅰ island in Vibrio cholerae

Objective To understand the distribution and variation of vibrio seventh pandemic island-Ⅰ (VSP-Ⅰ) in Vibrio cholerae. Methods All the genome data of V. cholerae were downloaded from GenBank of National Center for Biotechnology Information. VSP-Ⅰ sequence from the representative strain N16961of seventh cholera pandemic was used as reference, and VSP-Ⅰ island in these V. cholerae genomes were screened. MUMmer software was used to analyze single nucleotide polymorphism (SNP), and then OrthMCL software was used for homologous gene analysis, finally the BLAST software was used for sequence variation analysis and functional annotation. Results VSP-Ⅰ widely existed in V. cholerae, including all the seventh pandemic strains and the sequences were highly conserved. Among 105 seventh pandemic strains, 94 strains shared completely consistent VSP-Ⅰ, and 1-14 SNPs were only detected in remaining 11 strains respectively. The VSP-Ⅰ was also detected in two non-O1, non-O139 strains, however, compared with pandemic strain, sequence variations were observed, including insertion and deletion. Meanwhile, all these VSP-Ⅰ shared 9 conserved genes. VC0183 existed in all strains, but its size changed in the non-O1, non-O139 strains. In addition, VSP-Ⅰ carried five genes involved in its transfer and integration (VC0181-VC0185), including VC0178 encoding patatin-like protein, and VC0180 encoding peptidase. VC0178 and VC0180 might be associated with virulence. Conclusion As a specific genetic cluster within the seventh cholera pandemic strains, VSP-Ⅰ has been transferred to non O1, non O139 strains, and sequence variation has occurred.