Factors that influence the injection of Yop proteins by pathogenic Yersinia species into host cells during infection

The pathogenic Yersinia species, Y. enterocolitica , Y. pseudotuberculosis and Y. pestis, use a virulence plasmid-encoded type III secretion machinery to transport Yop proteins across the bacterial envelope. This type III secretion system is thought to promote the injection of some, but not all, Yop proteins into macrophages and other phagocytic cells during infection. However, this conjecture has hitherto not been demonstrated and the mechanistic events that lead to the specific injection of Yop proteins into host cells have not yet been revealed in molecular detail. Work presented herein has begun to characterize the role of lcrG and lcrV, two virulence plasmid encoded genes in regulating type III secretion and type III injection of Yop proteins using a tissue culture model of Yersinia infection. In an effort to identify additional genes and mechanisms that are involved in promoting type III secretion, a general search for mutants with defects in low calcium mediated growth inhibition were analyzed for type III secretion, identifying ttsA, a membrane protein as being essential for type III secretion of Y. entercolitica. Lastly, the role of Yersinia adhesins, YadA, InvA and the type I fimbriae PsaA or MyfA in Y. pseudotuberculosis and Y. enterocolitica, respectively were analyzed for type III secretion. These studies identified the requirement of some surface proteins for the type III injection pathway which was analyzed further by using a mouse model of infection for virulence and immunization studies.