Can Sb(III)-oxidizing prokaryote also oxidize As(III) under aerobic and anaerobic conditions, and vice versa?

Sb(III) and As(III) share similar chemical features and coexist in the environment. However, their oxidase enzymes have completely different sequences and structures. This raises an intriguing question: Could Sb(III)-oxidizing prokaryotes (SOPs) also oxidize As(III), and vice versa? Regarding this issue, previous investigations have yielded unclear, incorrect and even conflicting data. This work aims to address this matter. First, we prepared an enriched population of SOPs that comprises 55 different AnoA genes, lacking AioAB and ArxAB genes. We found that these SOPs can oxidize both Sb(III) and As(III) with comparable capabilities. To further confirm this finding, we isolated three cultivable SOP strains that have AnoA gene, but lack AioAB and ArxAB genes. We observed that they also oxidize both Sb(III) and As(III) under both anaerobic and aerobic conditions. Secondly, we obtained an enriched population of As(III)-oxidizing prokaryotes (AOPs) from As-contaminated soils, which comprises 69 different AioA genes, lacking AnoA gene. We observed that the AOP population has significant As(III)-oxidizing activities, but lack detectable Sb(III)-oxidizing activities under both aerobic and anaerobic conditions. Therefore, we convincingly show that a substantial number or most likely all of SOPs can oxidize As(III), but a significant amount or most likely all of AOPs cannot oxidize Sb(III). These findings clarify the previous ambiguities, confusion, errors or contradictions regarding how SOPs and AOPs oxidize each other's substrate. This study unveils important environmental implications as Sb(III) and As(III), sharing similar chemical traits, coexist in natural settings. Despite different oxidase enzymes, the investigation tackles a central question: Can Sb(III)-oxidizing prokaryotes (SOPs) oxidize As(III), and vice versa? The research clears up previous uncertainties, showing that a substantial number or most likely all of SOPs can effectively oxidize both Sb(III) and As(III) under both aerobic and anaerobic conditions. In contrast, a significant amount or most likely all of As(III)-oxidizing prokaryotes (AOPs) exhibit notable As(III)-oxidizing activities but lack Sb(III)-oxidizing capabilities. These findings provide insights into how SOPs and AOPs interact and oxidize each other's substrates, improving our understanding of the biogeochemical processes of antimony and arsenic in the environment.