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.