Proteomic Analysis Of Salmonella Enterica Serovar Typhimurium Adaptation To Host Conditions

Salmonella enterica serovar Typhimurium (S. Typhimurium) is an enteric pathogen that is capable of invading epithelial cells, leading to several manifestations of disease such as vomiting, gastroenteritis, inflammatory diarrhoea. After entering intestinal macrophages, S. Typhimurium can survive and replicate in this harsh environment. Through lymphatic system, S. Typhimurium can be spread to organs like spleen and liver, and cause systemic illness. Previous studies have clearly showed how S. Typhimurium invades epithelial cells. However, it remains unclear about the regulation events during S. Typhimurium adaptation to the microenvironment inside macrophages. Since many genes and proteins are involved in the pathogenesis of S. Typhimurium, a global proteomics study should provide comprehensive and unbiased discoveries at protein level.PhoP/PhoQ two-component system plays a central regulatory role in the pathogenesis of S. Typhimurium, and it can be activated by low [Mg2+] and sublethal concentrations of cationic antimicrobial peptides (CAMP). Since the PhoP/PhoQ system is also activated when S. Typhimurium is inside macrophages. growth media with low [Mg2+] or CAMP signals are often used to mimic the in vivo situation S. Typhimurium may encounter in macrophages. In this dissertation, we conducted quantitative proteomic analysis of S. Typhimurium grown under host-like condition. Our results provided new insights into S. Typhimurium adaptation into host environment.Using 2D-PAGE technique, we investigated the proteomic changes of S. Typhimurium under growth conditions with low [Mg2+] (PhoP-activating) or high [Mg2+] (PhoP-repressing). We found that many proteins were degraded during 3 h to 9 h growth under both conditions. Degraded proteins under low [Mg2+] condition (53) were much more than those under high [Mg2+] condition (20), with 16 degraded proteins in common. We consider that the widespread protein degradation is a strategy of S. Typhimurium used in response to host conditions. On the basis of a degradation-inducing signal (for the degradation of 16 mutual proteins in both [Mg2+] conditions), low [Mg2+] signal or the activated PhoP/PhoQ system may control the degration of many more proteins.Through a SILAC labeling technique combined with LC-MS/MS analysis, we performed a quantitative proteomic study of S. Typhimurium under several phagosome-mimicking conditions. In addition to the expression level changes of over 20 PhoP-regulated proteins, we also analyzed the regulation status of 52 metabolic pathways. We found that low [Mg2+] and C18G (one type of CAMP) had different influences on the PhoP/PhoQ regulatory network and certain metabolic activities. Together with previous knowledge of PhoP/PhoQ system, we proposed an adaptation model, which describes how S. Typhimurium differentially modulates its proteome through sensing different environmental conditions, in order to optimally adapt to various environmental conditions. The model provides new perspectives about Salmonella's adaptation to the host environment.