New Mobilization Pathway of Antimonite: Thiolation and Oxidation by Dissimilatory Metal-Reducing Bacteria via Elemental Sulfur Respiration.

Antimony (Sb) mobilization is widely explored with dissimilatory metal-reducing bacteria (DMRB) via microbial iron(III)-reduction. Here, our study found a previously unknown pathway whereby DMRB release adsorbed antimonite (Sb-O) from goethite via elemental sulfur (S) respiratory reduction under mild alkaline conditions. We incubated Sb-O-loaded goethite with MR-1 in the presence of S at pH 8.5. The incubation results showed that MR-1 reduced S instead of goethite, and biogenic sulfide induced the formation of thioantimonite (Sb-S). Sb-S was then oxidized by S to mobile thioantimonate (Sb-S), resulting in over fourfold greater Sb release to water compared with the abiotic control. Sb-S was identified as the intermediate during the oxidation process by Fourier transform ion cyclotron resonance mass spectrometry and electron spin resonance analysis. The existence of Sb-S reveals that the oxidation of Sb-S to Sb-S follows a two-step consecutive one-electron transfer from Sb to S atoms. Sb-S then links with Sb-S by sharing S atoms and inhibits Sb-S polymerization and SbS precipitation like a "capping agent". This study clarifies the thiolation and oxidation pathway of Sb-O to Sb-S by S respiration and expands the role of DMRB in the fate of Sb.