RPOS IS NECESSARY FOR BOTH THE POSITIVE AND NEGATIVE REGULATION OF STARVATION SURVIVAL GENES DURING PHOSPHATE, CARBON, AND NITROGEN STARVATION IN SALMONELLA-TYPHIMURIUM

The starvation stress response of Salmonella typhimurium encompasses t he genetic and physiologic changes that occur when this bacterium is s tarved for an essential nutrient such as phosphate (P), carbon (C), or nitrogen (N). The responses to the limitation of each of these nutrie nts involve both unique and overlapping sets of proteins important for starvation survival and virulence. The role of the alternative a fact or RpoS in the regulation of the starvation survival loci, stiA, stiB, and stiC, has been characterized. RpoS (sigma(S)) was found to be req uired for the P, C, and N starvation induction of stiA and stiC. In co ntrast, RpoS was found to be required for the negative regulation of s tiB during P and C starvation-induced stationary phase but not during logarithmic phase. This role was independent of the relA gene (previou sly found to be needed for stiB induction). The role of RpoS alone and in combination with one or more sti mutations in the starvation survi val of the organism was also investigated. The results clearly demonst rate that RpoS is an integral component of the complex interconnected regulatory systems involved in S. typhimurium's response to nutrient d eprivation. However, differential responses of various sti genes indic ate that additional signals and regulatory proteins are also involved.