The phage shock protein (Psp) system is a widely conserved bacterial extracytoplasmic stress response. It is induced in response to stimuli that may affect the cell envelope and reduce the proton-motive force. The mislocalization of outer membrane secretin proteins is a potent and specific Psp-inducing signal. Secretins are critical components of many virulence associated secretion systems. In the gastrointestinal pathogen Yersinia enterocolitica , the Psp system is essential for virulence. It permits bacterial survival during production of the Ysc type three secretion system, and specifically its YscC secretin component. At the beginning of this work the Y. enterocolitica Psp system was comprised of the PspF transcriptional activator and the pspABCDycjXF operon that it regulates. However, previous work suggested the presence of an unidentified component of the PspF regulon. The goal was to identify this component. A single open reading frame was identified as the additional member of the PspF regulon. This gene was named pspG and is predicted to encode an integral cytoplasmic membrane protein. Overexpression of pspG partially compensates for the loss of the entire pspA operon, both in vitro and in a mouse model of infection. pspG is conserved only in bacterial species that also have the unlinked pspA operon. PspG apparently shares a common function with PspB and PspC. All three are able to support bacterial growth during secretin mislocalization in the cell envelope. Intriguingly, pspG was also found to form a complex operon with the upstream gene dusA, which encodes a tRNA dihydrouridine synthase. This study has uncovered a new dimension to the Psp system that may have implications for other pathogenic bacteria. It lays the foundation for a deeper understanding of how bacteria handle stress associated with the production of widely conserved virulence-associated secretion systems.
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