Microbial dissolution of crystalline mercury sulfide via cysteine secretion

Mineral-associated mercury (Hg), predominantly as mercury sulfide (HgS), represents the largest environmental Hg reservoir and is typically considered immobile and inert. Here, we reveal a novel microbe-mediated mechanism for the bioleaching of crystalline HgS via cysteine secreted by microorganisms. Hg-resistant bacterial strains Arthrobacter sp. WS-B1, Massilia sp. WS-B3, and Serratia sp. WS-B5, isolated from Wanshan mining soils in China, were found to secrete cysteine, which promotes the disintegration of crystalline HgS into HgS nanoparticles (HgSNPs), dissolved Hg, and ultimately volatile Hg(0). Utilizing transmission electron microscopy with energy-dispersive X-ray spectroscopy, HgS breakdown was evidenced through the detection of HgSNPs and a broadened Hg:S ratio range from 1.08 ± 0.05 to 0.33–1.58. Time-of-flight secondary ion mass spectrometry analysis revealed the co-localisation of C 3 H 7 NO 2 S and Hg, indicating Hg–cysteine complexation. These complexes inhibited Hg precipitation, maintaining its bioavailability for crops, while also enabling photoreduction via ligand-to-metal charge transfer upon irradiation to detoxify soil Hg. This study sheds light on the microbial transformation of crystalline HgS, the formation pathways of HgSNPs in nature, and the enhanced bioavailability of Hg previously considered inert