Regulation of two distantly related structures important for virulence, the Ysa type III secretion system and the bacterial flagellum of Yersinia enterocolitica

High-virulent strains of the bacterial pathogen Yersinia enterocolitica maintain two different type III secretion (TTS) systems that have the capacity to target proteins into eukaryotic cells. One system, the Ysc TTS system, is encoded on a large virulence plasmid. The second system, the Ysa TTS system, is encoded by a region of the Y. enterocolitica chromosome called the ysa locus. This locus is composed of two divergently transcribed dusters of genes encoding the structural components of the Ysa TTS system and a set of secreted proteins called Ysps. Expression of ysa genes was examined in response to various environmental conditions. The analysis revealed the genes of the ysa locus are optimally expressed in high salt medium at neutral pH at 26°C. We also show that regulation of genes within the ysa locus requires the function of two signal transduction systems, the YsrS/YsrR two-component system and the RcsC/RcsB phosphorelay regulatory system. The results of this study provides a foundation for understanding how environmental signals are transduced by the regulatory systems composed of YsrRS and RcsCB affect activities of the Ysa TTS system during infection.; The components of the TTS apparatus are highly conserved among bacterial TTS systems as well as among components of the bacterial flagellum. Based on this homology, we study regulation of the flagellum of Y. enterocolitica in order to better understand regulation of TTS systems. Regulation of the genes encoding the flagellum of Y. enterocolitica is believed to be similar to that which has been documented for other members of the family Enterobacteriaceae, but little direct experimental evidence has been put forth to support this idea. In this study we show that flagellar genes in Y. enterocolitica are regulated by salt concentration and temperature and expression is controlled in a regulatory cascade similar to other Enterobacteriaceae. The motility master regulatory operon flhDC is required for the expression of genes with class II and class III promoters and the flagellar sigma factor, sigma 28, is required for expression of genes with class III promoters. This study lays the foundation for understanding the flagellar biosynthetic regulatory cascade in Y. enterocolitica.