A chromosomally encoded type III secretion pathway in Yersinia enterocolitica is important in virulence

Numerous Gram-negative bacteria use a type III, or contact dependent, secre tion system to deliver proteins into the cytosol of host cells. All of thes e systems identified to date have been shown to have a role in pathogenesis . We have identified 13 genes on the Yersinia enterocolitica chromosome tha t encode a type III secretion apparatus plus two associated putative regula tory genes. In order to determine the function of this chromosomally-encode d secretion apparatus, we created an in frame deletion of a gene that has h omology to the hypothesized inner membrane pore, ysaV. The ysaV mutant stra in failed to secrete eight proteins, called Ysps, normally secreted by the parental strain when grown at 28 degrees C in Luria-Bertani (LB) broth supp lemented with 0.4 M NaCl. Disruption of the ysaV gene had no effect on moti lity or phospholipase activity, suggesting this chromosomally encoded type III secretion pathway is distinct from the flagella secretion pathway of Y. enterocolitica. Deletion of the ysaV gene in a virulence plasmid positive strain had no effect on in vitro secretion of Yops by the plasmid-encoded t ype III secretion apparatus. Secretion of the Ysps was unaffected by the pr esence or absence of the virulence plasmid, suggesting the chromosomally en coded and plasmid-encoded type III secretion pathways act independently. Y. enterocolitica thus has three type III secretion pathways that appear to a ct independently. The ysaV mutant strain was somewhat attenuated in virulen ce compared with the wild type in the mouse oral model of infection (an app roximately 0.9 log difference in LD50). The ysaV mutant strain was nearly a s virulent as the wild type when inoculated intraperitoneally in the mouse model. A ysaV probe hybridized to sequences in other Yersinia spp. and homo logues were found in the incomplete Y. pestis genome sequence, indicating a possible role for this system throughout the genus.