A Comprehensive Assessment of the Genetic Determinants in Salmonella Typhimurium for Resistance to Hydrogen Peroxide Using Proteogenomics.

Salmonella is an intracellular pathogen infecting a wide range of hosts and can survive in macrophages. An essential mechanism used by macrophages to eradicate Salmonella is production of reactive oxygen species. Here, we used proteogenomics to determine the candidate genes and proteins that have a role in resistance of S. Typhimurium to H2 O2 . For Tn-seq, a saturated Tn5 insertion library was grown in vitro under either 2.5 (H2 O2 L) or 3.5 mM H2 O2 (H2 O2 H). We identified two sets of overlapping genes required for resistance of S. Typhimurium to H2 O2 L and H2 O2 H, and the results were validated via phenotypic evaluation of 50 selected mutants. The enriched pathways for H2 O2 resistance included DNA repair, aromatic amino acid biosynthesis (aroBK), Fe-S cluster biosynthesis, iron homeostasis and a putative iron transporter system (ybbKLM), and H2 O2 scavenging enzymes. Proteomics revealed that the majority of essential proteins, including ribosomal proteins, were downregulated upon exposure to H2 O2 . On the contrary, a subset of conditionally essential proteins identified by Tn-seq were analyzed by targeted proteomics, and 70% of them were upregulated by H2 O2 . The identified genes will deepen our understanding on S. Typhimurium survival mechanisms in macrophages, and can be exploited to develop new antimicrobial drugs.