The osnR gene of Corynebacterium glutamicum plays a negative regulatory role in oxidative stress responses

Among the Corynebacterium glutamicum ORFs that have been implicated in stress responses, we chose ORF cg3230, designated osnR, and analyzed it further. Unlike the osnR-deleted strain (ΔosnR), the osnR-overexpressing strain (P₁₈₀-osnR) developed growth defects and increased sensitivity to various oxidants including H₂O₂. Transcription in the P₁₈₀-osnR strain of genes such as sodA (superoxide dismutase), ftn (ferritin biosynthesis), and ahpD (alkyl hydroperoxide reductase; cg2674), which are involved in the detoxification of reactive oxygen species, was only 40% that of the wild type. However, transcription of katA, encoding H₂O₂-detoxifying catalase, was unchanged in this strain. Genes such as trxB (thioredoxin reductase) and mtr (mycothiol disulfide reductase), which play roles in redox homeostasis, also showed decreased transcription in the strain. 2D-PAGE analysis indicated that genes involved in redox reactions were considerably affected by osnR overexpression. The NADPH/NADP⁺ ratio of the P₁₈₀-osnR strain (1.35) was higher than that of the wild-type stain (0.78). Collectively, the phenotypes of the ΔosnR and P₁₈₀-osnR strains suggest a global regulatory role as well as a negative role for the gene in stress responses, particularly in katA-independent oxidative stress responses.