Unveiling the dual role of Paracoccus versutus XT0.6 in stibnite dissolution: from aerobic promotion to anaerobic inhibition

Microorganisms play a crucial role in the migration and transformation of antimony in mining areas, particularly under aerobic condition. However, whether and how microbes enhance the dissolution and oxidation of stibnite under anaerobic conditions remain poorly understood. This study used the facultative anaerobic antimony-oxidizing bacterium Paracoccus versutus XT0.6 to explore this under anaerobic conditions. XT0.6 couples the anaerobic oxidation of dissolved Sb(III) with denitrification, as indicated by shifts of antimony and nitrogen species. Interactions between XT0.6 and stibnite were conducted in closed systems with varying initial levels of oxygen (0%, 6%, 12%, 18%) and aerobic condition (21%). Results showed that XT0.6 inhibited the dissolution of stibnite and the release of Sb(III) within closed systems, regardless of the initial oxygen levels. This contrasts with aerobic conditions, where XT0.6 promoted stibnite dissolution and Sb release. In anaerobic abiotic closed system, total Sb concentration (TSb) was 41.7   mg/L with 16.8   mg/L as Sb(III). The presence of XT0.6 in the anaerobic closed system decreased TSb to 13.9   mg/L after day 3, with no Sb(III) detected. Similar patterns were observed in other closed systems with varying initial oxygen levels. Under aerobic condition, XT0.6 fully oxidized the released Sb(III) to Sb(V), resulting in a final concentration of 83.8   mg/L, while the abiotic control had a TSb of 69.8   mg/L with 36.3   mg/L as Sb(III). Light exposure enhanced chemical dissolution of stibnite (TSb 114.1   mg/L) and Sb(III) oxidation anaerobically but had no noticeable impact on microbial interaction with stibnite. As a semiconductor mineral, stibnite can generate reactive oxygen species upon light exposure, explaining the enhanced dissolution. The microbial inhibition of stibnite dissolution may be attributed to a passivation layer containing S-O bonds formed on the mineral surface by XT0.6 as demonstrated by XPS and SEM-EDS results. This study offers novel insights into the role of facultative anaerobic bacteria in antimony cycling, highlighting the importance of microbial-mineral interactions under anaerobic conditions.