ABSTRACTTheYersinia enterocoliticaYsa type III secretion system (T3SS) is associated with intracellular survival, and, like other characterized T3SSs, it is tightly controlled. Expression of theysagenes is only detected following growth at low temperatures (26°C) and in high concentrations of sodium chloride (290 mM) in the medium. The YsrSTR phosphorelay (PR) system is required forysaexpression and likely responds to NaCl. During our investigations into the Ysr PR system, we discovered that genes YE3578 and YE3579 are remarkably similar toysrRandysrS, respectively, and are probably a consequence of a gene duplication event. The amino acid differences between YE3578 andysrRare primarily clustered into two short regions. The differences between YE3579 andysrSare nearly all located in the periplasmic sensing domain; the cytoplasmic domains are 98% identical. We investigated whether these paralogs were capable of activatingysagene expression. We found that the sensor paralog, named DygS, is capable of compensating for loss ofysrS, but the response regulator paralog, DygR, cannot complement aysrRgene deletion. In addition, YsrR, but not DygR, interacts with the histidine phosphorelay protein YsrT. Thus, DygS likely activatesysagene expression in response to a signal other than NaCl and provides an example of a phosphorelay system in which two sensor kinases feed into the same regulatory pathway.IMPORTANCEAll organisms need mechanisms to promote survival in changing environments. Prokaryotic phosphorelay systems are minimally comprised of a histidine kinase (HK) that senses an extracellular stimulus and a response regulator (RR) but can contain three or more proteins. Through gene duplication, a unique hybrid HK was created. We show that, while the hybrid appears to retain all of the phosphorelay functions, it responds to a different signal than the original. Both HKs transmit the signal to the same RR, which activates a promoter that transcribes a set of genes encoding a type III secretion system (T3SS) whose function is not yet evident. The significance of this work lies in finding that two HKs regulate this T3SS, highlighting its importance.
Expression of the Yersinia enterocolitica pYV-Encoded Type III Secretion System Is Modulated by Lipopolysaccharide O-Antigen Status