However, the processing of K-check details antigen by the wbfF gene and possibly the adjacent wzz gene, and the regulation role of the upstream genes will
require further investigation. In both V. cholerae and V. vulnificus the capsule and O-antigen genes lie in a region similar to the O-antigen region of enteric, such as E. coli, and that specific genes may be shared by both biosynthetic pathways [6, 7]. Pandemic V. parahaemolyticus has changed rapidly in both O and K types, leading to the hypothesis that the genetic determinants of O and K also share the same genetic locus thus allowing a single genetic event to alter the structure of both antigens. However, our finding is not consistent with this hypothesis. Our experiments clearly demonstrated that genes determining the K-antigen in pandemic V. parahaemolyticus ICG-001 mw were located in the region determining
both surface polysaccharides in the other vibrios, but that the O-antigen genes are located elsewhere. From our data and Okura et al’s observations on polysaccharide Proteasome inhibition assay genes, we speculate that the region with homology to LPS core regions may be playing the role of O antigen. This speculation is consistent with the finding that the LPS in V. parahaemolyticus are rough type . Since the core genes are adjacent to the capsule genes, they could still be replaced in the same recombination event and give rise to both new O- and K-antigens. Analysis of putative O and K antigen genes in a different serotype O4:K68 revealed that these regions are distinct from those of O3:K6 serotype despite their highly similar genetic backbones  and suggested both the O and K regions were replaced during the serotype conversion (Chen et al: Comparative genomic analysis of Vibrio parahaemolyticus: serotype conversion and virulence, submitted). Conclusion Understanding
of the genetic basis of O- and K-antigens is critical to understanding the rapid changes in these polysaccharides seen in pandemic V. parahaemolyticus. This is also important in understanding the virulence of V. parahaemolyticus as the O- and K-antigens represent not major surface antigens responsible for protective immunity. In this study, we found the O and K genes were separated in V. parahaemolyticus but their locus maybe adjacent. This report also confirms the genetic location of K-antigen synthesis in V. parahaemolyticus O3:K6 allowing us to focus future studies of the evolution of serotypes to this region. Methods Bacterial strains and growth condition At the time of this study, we didn’t have access to the sequenced strain RIMD 2210633 and numerous studies showed that the pandemic strains of V. parahaemolyticus O3:K6 are highly clonal and homogenous in their genomes.