Structure and genetic basis of Yersinia similis serotype O:9 O-specific polysaccharide

The O-polysaccharide (OPS, O-Ag) cap of LPS is a major virulence factor of Yersinia species and also serves as a receptor for the binding of lytic bacteriophage φR1-37. Currently, the OPS-based serotyping scheme for the Yersinia pseudotuberculosis complex includes 21 known O-serotypes that follow three distinct lineages: Y. pseudotuberculosis sensu stricto, Y. similis and the Korean group of strains. Elucidation of the Y. pseudotuberculosis complex OPS structures and characterization of the OPS genetics (altogether 18 O-serotypes studied thus far) allows a better understanding of the relationships among the various O serotypes and will facilitate the analysis of the evolutionary processes giving rise to new serotypes. Here we present the characterization of the OPS structure and gene cluster of Y. similis O:9. Bacteriophage φR1-37, which uses the Y. similis O:9 OPS as a receptor, also infects a number of Y. enterocolitica serotypes, including O:3, O:5,27, O:9 and O:50. The Y. similis O:9 OPS structure resembled none of the receptor structures of the Y. enterocolitica strains, suggesting that φR1-37 can recognize several surface receptors, thus promoting broad host specificity.