O2-inducible H2O2-forming NADPH oxidase is responsible for the hyper O2 sensitivity of Bifidobacterium longum subsp. infantis

Abstract

Abstract Bifidobacteria are beneficial anaerobes, and their O2 sensitivity levels differ among species as a function of unknown molecular mechanisms. Bifidobacterium longum subspecies infantis (B. infantis), a predominant colonizer of the gastrointestinal tract of infants, showed a hyper O2-sensitive growth profile with accompanying a production of H2O2. In this study, we characterized an NADPH oxidase as a key enzyme responsible for this microbe’s hyper O2 sensitivity. A dominant active elution peak of H2O2-forming NADPH oxidase activity was detected in the first step of column chromatography, and the purified NADPH oxidase (NPOX) was identified as a homolog of nitroreductase family proteins. The introduction of the gene encoding B. infantis NPOX (npoxA) into O2-tolerant Bifidobacterium minimum made the strain O2 sensitive and allowed it to produce H2O2. Knockout of the npoxA gene in B. infantis decreased the production of H2O2 and mitigated its B. infantis hyper O2 sensitivity. A transcript of B. infantis npoxA is induced by O2, suggesting that the aerobic production of toxic H2O2 is functionally conserved in B. infantis.