Methionine Sulfoxide Reductase A (MsrA) Deficiency Affects the Survival ofMycobacterium smegmatiswithin Macrophages

Methionine sulfoxide reductase A (MsrA) is an antioxidant repair enzyme which reduces oxidized methionine to methionine. Since oxidation of methionine in proteins impairs their function, an absence of MsrA leads to abnormalities in different organisms, including alterations in the adherence patterns and in vivo survival of certain pathogenic bacteria. To understand the role of MsrA in intracellular survival of bacteria, we disrupted the gene encoding MsrA inMycobacterium smegmatisthrough homologous recombination. ThemsrAmutant strain ofM. smegmatisexhibited significantly reduced intracellular survival in murine J774A.1 macrophages compared to the survival of its wild-type counterpart. Furthermore, immunofluorescence and immnunoblotting of phagosomes containingM. smegmatisstrains revealed that the phagosomes with themsrAmutant strain acquired both p67phoxof phagocyte NADPH oxidase and inducible nitric oxide synthase much earlier than the phagosomes with the wild-type strain. In addition, themsrAmutant strain ofM. smegmatiswas observed to be more sensitive to hydroperoxides than the wild-type strain was in vitro. These results suggest that MsrA plays an important role in both extracellular and intracellular survival ofM. smegmatis.