Genetic variation of capsule/LPS biogenesis in two serogroup O31 Vibrio cholerae isolates

Complete genome sequence of the marine fish pathogen Vibrio anguillarum harboring the pJM1 virulence plasmid and genomic comparison with other virulent strains of V. anguillarum and V. ordalii

We dissected the complete genome sequence of the O1 serotype strain Vibrio anguillarum 775(pJM1) and determined the draft genomic sequences of plasmidless strains of serotype O1 (strain 96F) and O2β (strain RV22) and V. ordalii. All strains harbor two chromosomes, but 775 also harbors the virulence plasmid pJM1, which carries the anguibactin-producing and cognate transport genes, one of the main virulence factors of V. anguillarum. Genomic analysis identified eight genomic islands in chromosome 1 of V. anguillarum 775(pJM1) and two in chromosome 2. Some of them carried potential virulence genes for the biosynthesis of O antigens, hemolysins, and exonucleases as well as others for sugar transport and metabolism. The majority of genes for essential cell functions and pathogenicity are located on chromosome 1. In contrast, chromosome 2 contains a larger fraction (59%) of hypothetical genes than does chromosome 1 (42%). Chromosome 2 also harbors a superintegron, as well as host "addiction" genes that are typically found on plasmids. Unique distinctive properties include homologues of type III secretion system genes in 96F, homologues of V. cholerae zot and ace toxin genes in RV22, and the biofilm formation syp genes in V. ordalii. Mobile genetic elements, some of them possibly originated in the pJM1 plasmid, were very abundant in 775, resulting in the silencing of specific genes, with only few insertions in the 96F and RV22 chromosomes.

Genetic analysis of the capsule polysaccharide (K antigen) and exopolysaccharide genes in pandemic Vibrio parahaemolyticus O3:K6

BACKGROUND

Pandemic Vibrio parahaemolyticus has undergone rapid changes in both K- and O-antigens, making detection of outbreaks more difficult. In order to understand these rapid changes, the genetic regions encoding these antigens must be examined. In Vibrio cholerae and Vibrio vulnificus, both O-antigen and capsular polysaccharides are encoded in a single region on the large chromosome; a similar arrangement in pandemic V. parahaemolyticus would help explain the rapid serotype changes. However, previous reports on "capsule" genes are controversial. Therefore, we set out to clarify and characterize these regions in pandemic V. parahaemolyticus O3:K6 by gene deletion using a chitin based transformation strategy.

RESULTS

We generated different deletion mutants of putative polysaccharide genes and examined the mutants by immuno-blots with O and K specific antisera. Our results showed that O- and K-antigen genes are separated in V. parahaemolyticus O3:K6; the region encoding both O-antigen and capsule biosynthesis in other vibrios, i.e. genes between gmhD and rjg, determines the K6-antigen but not the O3-antigen in V. parahaemolyticus. The previously identified "capsule genes" on the smaller chromosome were related to exopolysaccharide synthesis, not K-antigen.

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 report 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.