Induction of RpoS degradation by the two-component system regulator RstA in Salmonella

Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Técnicas

^* To whom correspondence should be addressed. Email: garciavescovi{at}ibr.gov.ar.

	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 bacteria to cope with extra- and intra-cellular harsh environments. In this work, we found that expression of Salmonella RstA, a response regulator from the two-component system family, was able to down-regulate the expression of three RpoS-controlled genes (narZ, spvA and bapA). Furthermore, this down-regulation was achieved by the reduction in RpoS cellular levels. The alternative sigma factor RpoS is critical for the bacterial endurance to most stressful conditions including stationary phase entrance and host adaptation. Accordingly, RpoS cellular levels are tightly controlled by complex transcriptional, translational and post-translational 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 been previously 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.