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 metalreducing bacteria (DMRB) via microbial iron(III)-reduction. Here, our study found a previously unknown pathway whereby DMRB release adsorbed antimonite (Sb-III-O) from goethite via elemental sulfur (S-0) respiratory reduction under mild alkaline conditions. We incubated Sb-III-O-loaded goethite with Shewanella oneidensis MR-1 in the presence of S-0 at pH 8.5. The incubation results showed that MR-1 reduced S-0 instead of goethite, and biogenic sulfide induced the formation of thioantimonite (Sb-III-S). Sb-III-S was then oxidized by S-0 to mobile thioantimonate (Sb-V-S), resulting in over fourfold greater Sb release to water compared with the abiotic control. Sb-IV-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-IV-S reveals that the oxidation of Sb-III-S to Sb-V-S follows a two-step consecutive one-electron transfer from Sb to S atoms. Sb-V-S then links with Sb-III-S by sharing S atoms and inhibits Sb-III-S polymerization and (Sb2S3)-S-III precipitation like a "capping agent". This study clarifies the thiolation and oxidation pathway of Sb-III-O to Sb-V-S by S-0 respiration and expands the role of DMRB in the fate of Sb.