Proteomic Profiling during Infection Distinguishes the Intracellular Environment of Host Cells.

Essential to bacterial pathogenesis, Salmonella enterica serovar Typhimurium ( Typhimurium) has evolved the capacity to quickly sense and adapt to specific intracellular environment within distinct host cells. Here we examined Typhimurium proteomic remodeling within macrophages, allowing direct comparison with our previous studies in epithelial cells. In addition to many shared features, our data revealed proteomic signatures highly specific to one type of host cells. Notably, intracellular Typhimurium differentially regulates the two type III secretion systems (T3SSs) far more quickly in macrophages than in epithelial cells; bacterial flagellar and chemotaxis systems degenerate more quickly in macrophages than in HeLa cells as well. Importantly, our comparative analysis uncovered high levels of induction of bacterial histidine biosynthesis in macrophages but not in epithelial cells. Targeted metabolomic measurements revealed markedly lower histidine levels within macrophages. Intriguingly, further functional studies established that histidine biosynthesis that is defective (due to a mutation) renders the bacterium (strain SL1344) hypersensitive to intracellular shortage of this amino acid. Indeed, another Typhimurium strain, namely, strain 14028s, with a fully functional biosynthetic pathway exhibited only minor induction of the operon within infected macrophages. Our work thus provided novel insights into Typhimurium adaptation mechanisms within distinct host cells and also provided an elegant paradigm where proteomic profiling of intracellular pathogens is utilized to discriminate specific host environments (e.g., on the basis of nutrient availability). Typhimurium is one of the leading causes of foodborne bacterial infection. Nevertheless, how adapts to distinct types of host cells during infection remains poorly understood. By contrasting intracellular proteomes from both infected macrophages and epithelial cells, we found striking proteomic signatures specific to particular types of host cells. Notably, proteomic remodeling exhibited quicker kinetics in macrophages than in epithelial cells with respect to bacterial virulence and flagellar and chemotaxis systems. Furthermore, we unveiled high levels of induction of bacterial histidine biosynthesis in macrophages but not in epithelial cells, which is attributable to differing intracellular levels of this amino acid. Intriguingly, we found that a defective gene renders a strain hypersensitive to histidine shortage in macrophages. Overall, our work reveals specific adaptation mechanisms in distinct host cells, which should aid in the development of novel anti-infection strategies.