Enhanced microbial degradation of methylmercury by montmorillonite

Abstract

The potent neurotoxic methylmercury (MeHg) can be detoxified through microbial demethylation. The colonization and functions of microbes are influenced by minerals in the environment; however, the role of minerals in mediating microbial degradation of MeHg remains poorly understood. Here, we investigated the effects of three typical soil minerals (i.e., montmorillonite, ferrihydrite, and birnessite) on MeHg degradation by Chitinophaga dinghuensis. The addition of montmorillonite increased the MeHg degradation efficiency by C. dinghuensis from 27.27 % to 44.84 % in 120 h, representing a 1.6-fold improvement compared to the mineral-free system, whereas ferrihydrite or birnessite had negligible effects on the MeHg degradation. This could be attributed that montmorillonite offered bacterial colonization surfaces for survival and alleviated MeHg-induced cell toxicity by reducing the production of intracellular reactive oxygen species. Additionally, montmorillonite released magnesium ions to improve cell metabolisms for the mineral-enhanced demethylation of MeHg. We also found that Fe²⁺ oxidation at the bacteria-montmorillonite interface could further contribute to the enhanced MeHg degradation by bacteria. Together, our work provides new insights into the crucial role of montmorillonite in mediating microbially-driven MeHg degradation, with important implications for understanding Hg biogeochemical cycles and mitigating environmental risks of the neurotoxin.