Methionine sulfoxide reductases gene deletion strains of Salmonella Typhimurium accumulate higher order of protein oligomers, show impaired intraphagocytic survival and defective colonization in poultry.

Abstract

By repairing oxidized methionine (Met-SO) residues, methionine sulfoxide reductases (Msrs) play important role in survival and virulence of Salmonella Typhimurium (S. Typhimurium). Salmonella encodes five msrs. Through the generation of single and cumulative deletion mutants (ΔmsrA, ΔmsrP, ΔmsrAC, ΔmsrACP, ΔmsrACPB, and ΔmsrACPBbisC), we analyzed the relative contribution of various msr genes (msrA, msrB, msrC, msrP, and bisC) in oxidative stress survival of S. Typhimurium. We evaluated the effects of msr gene deletion(s) on protein oligomerization, survival in immune cells, colonization in poultry organs, and induction of immune responses. The mutant strains exhibited elevated levels of higher-order of protein oligomers, with the ΔmsrACPBbisC strain accumulating the highest levels of protein oligomers. Survival assays in macrophages and dendritic cells demonstrate that the msrA, and msrC genes play critical roles in proliferation of S. Typhimurium in immune cells, whereas the contribution of msrP is minimal. The msr mutants showed defective cecal colonization and systemic dissemination to the spleen and liver of poultry birds, the degree of which depends on the number of mutations. Birds inoculated with msr mutant strains showed modulated humoral as well as cellular immune responses as compared to S. Typhimurium infected counterpart. These findings underscore the critical roles of msr genes in colonization of S. Typhimurium in poultry and modulation of immune responses, and have implications in the design and development of prophylaxis against S. Typhimurium for poultry.