Novel Bifunctional Enzyme AntO Catalyzes Antimonite Oxidation and H 2 O 2 Decomposition in Environmental Antimony Detoxification

Microbial oxidation of environmental antimonite (Sb(III)) to antimonate (Sb(V)) is a key antimony (Sb) detoxification mechanism. Comamonas testosteroni JL40 oxidizes Sb(III) to Sb(V) under oxic conditions via an uncharacterized mechanism. A redox-related enzyme identified via differential proteomics was designated AntO. The antO transcription was significantly upregulated upon addition of Sb(III). AntO is predicted to be a catalase-like heme-binding peroxidase, similar to the uncharacterized SrpA. Phylogenetic analysis indicates that AntO represents a novel Sb(III) oxidase or catalase. In E. coli AW3110(Δars), AntO confers Sb(III) resistance and oxidation activity and is induced by Sb(III) and H2O2. Further analysis confirms that antO mediates Sb(III) oxidation and H2O2 decomposition in JL40. Purified AntO catalyzes Sb(III) oxidation (with NADP+ as an electron acceptor) and H2O2 decomposition in vitro. Molecular docking shows that these reactions occur in distinct AntO structural domains. In summary, AntO has dual roles: Sb(III) oxidation for detoxification and H2O2 decomposition. This study identifies AntO as a novel environmental Sb(III) oxidase that facilitates Sb(III) detoxification, alleviates Sb(III)-induced oxidative stress, and advances understanding of microbial contributions to antimony biogeochemical cycling.