Quantitative proteomic analysis of Salmonella enterica serovar Typhimurium under PhoP/PhoQ activation conditions

The PhoP/PhoQ two-component system plays a central regulatory role in the pathogenesis of Salmonella enterica serovar Typhimurium (S. Typhimurium), and it can be activated by low Mg(2+) concentrations and sublethal concentrations of cationic antimicrobial peptides (CAMP). Therefore, these two PhoP/PhoQ activation signals are considered as in vivo environmental cues sensed by S. Typhimurium for adaptation and survival. In this work, we conducted a SILAC (stable isotope labeling by amino acids in cell culture)-based quantitative proteomic study to survey the proteomic changes of S. Typhimurium in response to low Mg(2+) concentrations or CAMP. We discovered that CAMP activated a portion of the PhoP/PhoQ regulatory network, whereas low Mg(2+) concentrations upregulated nearly all known members of this network, a number of previously unknown proteins, and some proteins regulated by IHF and RpoS. Systematic analysis following metabolic pathways revealed that low Mg(2+) concentrations selectively influenced proteins of certain metabolic functions while CAMP did not. Our study indicates that the low Mg(2+)-concentration condition may lead S. Typhimurium into a growth-control lifestyle, which provides new perspectives about Salmonella's adaptation to the host environment.