RpoS-dependent expression of OsmY in Salmonella enterica serovar typhi: activation under stationary phase and SPI-2-inducing conditions.

OsmY is a periplasmic protein with two BON domains which may attach to phospholipid membranes. Previous reports showed that the expression of OsmY in Escherichia coli was hyperosmotically inducible and RpoS dependent. But little work was done to investigate the expression and function of OsmY in Salmonella. Here, we detected the endogenous OsmY in Salmonella enterica serovar Typhi (S. Typhi) with polyclonal antibody. The results showed that the expression of OsmY was also RpoS dependent and was activated under stationary phase. Further, using in vitro culture, we established the Salmonella pathogenesis island (SPI)-1 and SPI-2-inducing conditions with hyperosmolarity and low-phosphate, low-magnesium medium (pH 5.8), respectively, and found that only SPI-2-inducing conditions can activate the expression of OsmY. osmY deletion mutant showed delayed growth compared with wild-type S. Typhi in SPI-2-inducing conditions. The results indicated that OsmY may function to resist the stress and be favorable for Salmonella's replication in the Salmonella-containing vesicles of macrophage.