σS-Mediated Stress Response Induced by Outer Membrane Perturbation Dampens Virulence in Salmonella enterica serovar Typhimurium

Abstract

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

Role of RpoS in Regulating Stationary Phase Salmonella Typhimurium Pathogenesis-Related Stress Responses under Physiological Low Fluid Shear Force Conditions

“…All the phenotypes tested in this study have previously been shown to be regulated by RpoS in stationary-phase Salmonella enterica pathovars cultured conventionally ( 26 , 28 , 33 , 40 – 42 , 44 – 47 , 86 , 90 ). However, there is surprisingly little information regarding the impact of physiological fluid shear conditions on RpoS regulation of stationary-phase Salmonella pathogenesis-related responses.…”

“…As RpoS directly or indirectly regulates diverse pleiotropic Salmonella phenotypes, it is not surprising that RpoS-mediated gene expression is controlled at multiple levels, including mRNA and protein via modification of transcriptional and translational activity, as well as abundance and stability of the respective biological products ( 46 , 47 , 50 – 58 ). In addition, the expression of RpoS itself is associated with complex regulation, including translational regulation by the RNA binding protein Hfq ( 30 , 59 – 67 ).…”

Cyclic di-GMP Modulates a Metabolic Flux for Carbon Utilization in Salmonella enterica Serovar Typhimurium

“…The binding of Cra-His 6 to P fruB , P ptsG , and P manX was examined using EMSA, as described previously ( 81 , 83 , 84 ), with slight modifications. DNA fragments comprising the promoter regions of fruB , ptsG , and manX were PCR-amplified using the primers listed in Table S2 and purified using the Wizard SV Gel and PCR Clean-Up System (Promega).…”

RpoS activates formation ofSalmonellaTyphi biofilms and drives persistence in the gall bladder

“…Further understanding will also require investigating a possible co-regulatory function of Crl in stimulating the RpoS activity to enable transcriptional activation, as determined for other RpoS-responsive genes, for example, the csg operon, adrA and ssrA [63,[76][77][78] . Overall, the presence of other quintessential RpoSregulated genes, such as dps, bolA, uspA and osmB, in our Tn-ClickSeq dataset (Supplementary Fig.…”

“…His6-tagged RpoS protein was purified from an E. coli DH5 strain transformed with the plasmid pUHE21-lacI q ::rpoS [63] (expresses RpoS from STm 14028s strain which is 100% identical to RpoS from STy H58) following the protocol as described in…”