9.B.100 The Phage Shock Protein (Psp) Family

The phage shock protein (Psp) system is induced by extracytoplasmic stress and thought to be important for the maintenance of the proton motive force. Karlinsey et al. (2010) investigated the contribution of PspA to Salmonella virulence. A pspA deletion mutation attenuates virulence of Salmonella enterica serovar Typhimurium following intraperitoneal inoculation of C3H/HeN (Ity(r) ) mice. PspA was found to be specifically required for virulence in mice expressing the natural resistance-associated macrophage protein 1 (Nramp1) (Slc11a1) divalent metal transporter, which restricts microbial growth by limiting the availability of essential divalent metals within the phagosome. Salmonella competes with Nramp1 by expressing multiple metal uptake systems including the Nramp-homologue MntH, the ABC transporter SitABCD and the ZIP family transporter ZupT. PspA was found to facilitate Mn²⁺ transport by MntH and SitABCD, as well as Zn²⁺ and Mn²⁺ transport by ZupT. In vitro uptake of (54) Mn²⁺ by MntH and ZupT was reduced in the absence of PspA. Transport-deficient mutants exhibit reduced viability in the absence of PspA when grown under metal-limited conditions. Moreover, the ZupT transporter is required for Salmonella enterica virulence in Nramp1-expressing mice. Karlinsey et al. (2010) propose that PspA promotes Salmonella virulence by maintaining proton motive force, which is required for the function of multiple transporters mediating bacterial divalent metal acquisition during infection.