Genomic dissection of the O-serogroup global reference strains: reassessing our view of diversity and plasticity between two chromosomes.

Approximately 200 O-serogroups of have already been identified; however, only 2 serogroups, O1 and O139, are strongly related to pandemic cholera. The study of non-O1 and non-O139 strains has hitherto been limited. Nevertheless, there are other clinically and epidemiologically important serogroups causing outbreaks with cholera-like disease. Here, we report a comprehensive genome analysis of the whole set of O-serogroup reference strains to provide an overview of this important bacterial pathogen. It revealed structural diversity of the O-antigen biosynthesis gene clusters located at specific loci on chromosome 1 and 16 pairs of strains with almost identical O-antigen biosynthetic gene clusters but differing in serological patterns. This might be due to the presence of O-antigen biosynthesis-related genes at secondary loci on chromosome 2.