Mechanism of extracellular electron transport and reactive oxygen mediated Sb(III) oxidation by Klebsiella HC10

Microbial oxidation and the mechanism of Sb(III) are key governing elements in biogeochemical cycling. A novel Sb oxidizing bacterium, K. aerogenes HC10, was attracted early and revealed that extracellular metabolites were the main fractions driving Sb oxidation. However, linkages between the extracellular metabolite driven Sb oxidation process and mechanism remain elusive. Here, model phenolic and quinone compounds, i.e., anthraquinone2,6-disulfonate (AQDS) and hydroquinone (HYD), representing extracellular oxidants secreted by K. aerogenes HC10, were chosen to further study the Sb(III) oxidation mechanism. N2 purging and free radical quenching showed that oxygen -induced oxidation accounted for 36.78% of Sb(III) in the metabolite reaction system, while hydroxyl free radicals ( center dot OH) accounted for 15.52%. center dot OH and H2O2 are the main driving factors for Sb oxidation. Radical quenching, methanol purification and electron paramagnetic resonance (EPR) analysis revealed that center dot OH, superoxide radical (O2 center dot-) and semiquinone (SQ-center dot) were reactive intermediates of the phenolic induced oxidation process. Phenolic -induced ROS are one of the main oxidants in metabolites. Cyclic voltammetry (CV) showed that electron transfer of quinone also mediated Sb(III) oxidation. Part of Sb(V) was scavenged by the formation of the secondary Sb(V)-bearing mineral mopungite [NaSb(OH)6] in the incubation system. Our study demonstrates the microbial role of oxidation detoxification and mineralization of Sb and provides scientific references for the biochemical remediation of Sb-contaminated soil. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.