Antimonite oxidation by microbial extracellular superoxide in Pseudomonas sp. SbB1

Antimony (Sb) is a re-emerging contaminant, and its redox transformation is mainly driven by microorganisms. Sb(III) oxidation has been attributed to enzymatic catalyzed reaction, though the physiological reason for this process remains unclear. Herein, we isolated a bacterium named Pseudomonas sp. SbB1 which can oxidize Sb(III) to Sb(V) without known Sb-oxidizing genes in its genome. The Sb(III) oxidation followed a zero-order kinetics with an appreciably lower rate (0.068 mu M/h) than known Sb(III) oxidases (0.159-0.210 mu M/h). Our incubation experiments show that Sb(III) was oxidized by extracellular superoxide and the superoxide production is NADH-dependent. By in-gel analysis and Sb K-edge XANES, we found proteins at similar to 100 kDa position were responsible for Sb(III) oxidation by producing superoxide. Further, our nano LC-MS/MS results suggest that dihydrolipoyl dehydrogenase was the source of extracellular superoxide. In vivo evidence with mutant indicated that strain Delta DdldH was incapable of producing superoxide and oxidizing Sb(III), whereas complementation by dldH rescued the mutant's ability. Beyond strain SbB1, superoxide generation and Sb(III) oxidation were also observed in diverse bacteria with DLDH orthologous across five classes. Our finding shows a previously unknown pathway used by widespread bacteria to mediate the transformation of redox-sensitive pollutants in the environment. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

A bacterium named Pseudomonas sp. SbB1 was isolated, capable of oxidizing Sb(III) to Sb(V) without known Sb-oxidizing genes. The oxidation process is NADH-dependent and involves proteins producing extracellular superoxide at approximately 100 kDa. This previously unknown pathway has been observed in diverse bacteria and provides insight into the transformation of redox-sensitive pollutants in the environment.