Induction of RpoS Degradation by the Two-Component System Regulator RstA in Salmonella enterica

Abstract

Bacterial survival in diverse and changing environments relies on the accurate interplay between different regulatory pathways, which determine the design of an adequate adaptive response. The proper outcome depends on a precise gene expression profile generated from the finely tuned and concerted action of transcriptional factors of distinct regulatory hierarchies. Salmonella enterica serovar Typhimurium harbors multiple regulatory systems that are crucial for the bacterium to cope with harsh extra-and intracellular environments. In this work, we found that the expression of Salmonella RstA, a response regulator from the two-component system family, was able to downregulate the expression of three RpoS-controlled genes (narZ, spvA, and bapA). Furthermore, this downregulation was achieved by a reduction in RpoS cellular levels. The alternative sigma factor RpoS is critical for bacterial endurance under the most-stressful conditions, including stationary-phase entrance and host adaptation. Accordingly, RpoS cellular levels are tightly controlled by complex transcriptional, translational, and posttranslational mechanisms. The analysis of each regulatory step revealed that in Salmonella, RstA expression was able to promote RpoS degradation independently of the MviA-ClpXP proteolytic pathway. Additionally, we show that RstA is involved in modulating Salmonella biofilm formation. The fact that the RpoS-modulated genes affected by RstA expression have previously been demonstrated to contribute to Salmonella pathogenic traits, which include biofilm-forming capacity, suggests that under yet unknown conditions, RstA may function as a control point of RpoS-dependent pathways that govern Salmonella virulence.RstA is a member of the OmpR subfamily of two-component system (TCS) response regulators (RRs), characterized by the display of a winged-helix-turn-helix motif in the DNAbinding domain. Several lines of evidence demonstrated that in Escherichia coli, the encoding gene, rstA, belongs to the PhoP/ PhoQ regulon (39) showing downregulation of rstAB (which codes for the putative RstA/RstB TCS putative pair) in a phoPQ mutant strain and direct PhoP control over rstA expression by a footprinting assay (34). Yamamoto et al. showed that RstB, the putative RstA-associated histidine kinase, was able to transfer in vitro its phosphoryl group to RstA (53), suggesting that in E. coli, RstB and RstA constitute an orthodox TCS regulatory pair. Phenotypic screenings, either systematically deleting the genes that code for TCS or overexpressing all RRs, indicated that E. coli rstAB was involved in bacterial resistance to ketoprofen, pridinol, and troleandomycin (54) and that RstA overexpression conferred low-level ␤-lactam resistance (20). More recently, it was shown that in E. coli, the transient expression of RpoE (sigma E) in stationary phase downregulated rstA and rstB transcription (22) and that multiple copies of rstA suppressed the lethal phenotype of a deletion in yjeE, encoding an ATPase with undetermined function (6). While thi...

Effect of Flagellar Mutations on Yersinia enterocolitica Biofilm Formation

“…RpoS also plays a complex role in the regulation of biofilms. In S. enterica and Vibrio sp., mutations in rpoS repressed the development of biofilms (8), and in E. coli MG1655, the rpoS mutation repressed the maturation of biofilms (36). In contrast, the rpoS mutation enhanced biofilm formation in E. coli K-12 and Pseudomonas sp.…”

Regulation of the Escherichia coli csgD promoter: interplay between five transcription factors

“…2b, lane 5) while overproduction of RstA resulted in significant reduction of csgD mRNA (Ogasawara et al, 2007a), these results together indicating a negative role of RstA in csgD transcription. In the absence of RstA, however, translation of rpoS is enhanced (Sugiura et al, 2003) while overproduction of RstA induces degradation of RpoS in Salmonella (Cabeza et al, 2007). Thus the observed change in csgD transcription at neutral pH might not be the direct consequence of the change in repressor RstA level but a result of the change of RpoS level.…”

RstA-Promoted Expression of the Ferrous Iron Transporter FeoB under Iron-Replete Conditions Enhances Fur Activity in Salmonella enterica

“…However, low pH does not seem to produce sufficient levels of active RstA (i.e., phosphorylated RstA) in E. coli because repression of csgD transcription occurred only upon overexpression of the RstA protein from a plasmid (19). In Salmonella enterica, overexpression of the RstA protein lowered the levels of the alternative sigma factor RpoS by an unknown mechanism, which consequently downregulated transcription of three RpoS-controlled genes, narZ, spvA, and bapA, in stationary phase (4). Consistent with the role of the BapA protein in biofilm formation (14,29), RstA expression impaired Salmonella's ability to develop a biofilm (4).…”