Comparative genomics for non-O1/O139 Vibrio cholerae isolates recovered from the Yangtze River Estuary versus V. cholerae representative isolates from serogroup O1.

Vibriocholerae, which is autochthonous to estuaries worldwide, can cause human cholera that is still pandemic in developing countries. A number of V. cholerae isolates of clinical and environmental origin worldwide have been subjected to genome sequencing to address their phylogenesis and bacterial pathogenesis, however, little genome information is available for V. cholerae isolates derived from estuaries, particularly in China. In this study, we determined the complete genome sequence of V. cholerae CHN108B (non-O1/O139 serogroup) isolated from the Yangtze River Estuary, China and performed comparative genome analysis between CHN108B and other eight representative V. cholerae isolates. The 4,168,545-bp V. cholerae CHN108B genome (47.2% G+C) consists of two circular chromosomes with 3,691 predicted protein-encoding genes. It has 110 strain-specific genes, the highest number among the eight representative V. cholerae whole genomes from serogroup O1: there are seven clinical isolates linked to cholera pandemics (1937-2010) and one environmental isolate from Brazil. Various mobile genetic elements (such as insertion sequences, prophages, integrative and conjugative elements, and super-integrons) were identified in the nine V. cholerae genomes of clinical and environmental origin, indicating that the bacterium undergoes extensive genetic recombination via lateral gene transfer. Comparative genomics also revealed different virulence and antimicrobial resistance gene patterns among the V. cholerae isolates, suggesting some potential virulence factors and the rising development of resistance among pathogenic V. cholerae. Additionally, draft genome sequences of multiple V. cholerae isolates recovered from the Yangtze River Estuary were also determined, and comparative genomics revealed many genes involved in specific metabolism pathways, which are likely shaped by the unique estuary environment. These results provide additional evidence of V. cholerae genome plasticity and will facilitate better understanding of the genome evolution and pathogenesis of this severe water-borne pathogen worldwide.