A proteomic analysis of the osmotic shock response in Salmonella enterica serovar Typhimurium

A reliable 2-dimensional gel electrophoresis methodology for the analysis of the Salmonella Typhimurium proteome was established and combined with mss spectrometry to detect and identify proteins that were differentially expressed when Salmonella was exposed to hyper-osmotic stress. In wild type S. Typhimurium 24 proteins were differentially expressed, 13 were up-regulated and 11 down-regulated. The proteins identified were involved in a range of bacterial systems including protein handling, protein synthesis, detoxification, metabolism and cell morphogenesis. In addition, an ompR- mutant was used to determine which of these differentially expressed proteins were regulated by or independent of the OmpR/EnvZ regulatory system. Generally, a similar set of components were differentially expressed in the ompR- mutant. However, the degree of induction or repression tended to be exaggerated. Additional analyses using the non-gel LC/MS based Protein Expression SystemTM strongly supported these results, further highlighting the up-regulation of proteins involved in cell morphogenesis, and also suggesting a subtle down-regulation of TCA cycle components. Two of the proteins that were highly induced by hyper-osmotic stress, and implicated in determining cell shape, where MreB and YgaU (the later was the most strongly induced protein, as detected by 2-D gel analyses, in both Salmonella strains). Further mRNA analyses indicated that YgaU is transcriptionally up-regulated under hyper-osmotic stress, whereas MreB appears to be post-transcriptionally controlled. Mutational analysis also confirmed that MreB is involved in cell morphology in Salmonella.