σ-Mediated Stress Response Induced by Outer Membrane Perturbation Dampens Virulence in serovar Typhimurium.

alters cellular processes as a strategy to improve its intracellular fitness during host infection. Alternative factors are known to rewire cellular transcriptional regulation in response to environmental stressors. σ factor encoded by the gene is a key regulator required for eliciting the general stress response in many proteobacteria. In this study, Typhimurium deprived of an outer membrane protein YcfR was attenuated in intracellular survival and exhibited downregulation in pathogenicity island-2 (SPI-2) genes. This decreased SPI-2 expression caused by the outer membrane perturbation was abolished in the absence of . Interestingly, regardless of the defects in the outer membrane integrity, RpoS overproduction decreased transcription from the common promoter of and , which encode a two-component regulatory system for SPI-2. RpoS was found to compete with RpoD for binding to the P region, and its binding activity with RNA polymerase (RNAP) to form Eσ holoenzyme was stimulated by the small regulatory protein Crl. This study demonstrates that undergoing RpoS-associated stress responses due to impaired envelope integrity may reciprocally downregulate the expression of SPI-2 genes to reduce its virulence.