Identification of hydrogen oxidation coupled with antimonate reduction, a novel antimony biogeochemical cycling, in two contrasting antimony-contaminated environments

Antimony (Sb) contamination is a serious environmental problem owing to its extensive production worldwide. High concentration of Sb is often detected in mining-contaminated environments, leading to the risk of contamination to the downstream environments through waterflow. Microorganisms play an important role in the fate and transport of Sb. Microbially mediated Sb(V) reduction performs an important environmental service because it can reduce the mobility of Sb and prevent the transport of Sb to downstream. As a commonly found intermediate in mining and aquatic environments, molecular hydrogen (H2) may serve as an electron donor to drive Sb(V) reduction, although this biogeochemical process has not yet been reported. In this study, Sb(V) reduction coupled with H2 oxidation (HOSbR) was identified in two contrasting Sb-contaminated habitats, i.e., oligotrophic tailings and organic-rich river sediments. DNA-stable isotope probing identified Azospirillum and Hydrogenophaga spp. as the bacteria potentially responsible for HOSbR in oligotrophic tailings and organic-rich river sediments, respectively. Further, Azospirillum spp. were identified as keystone taxa in tailings. The causal inference framework suggested that Azospirillum spp. may contribute to the increased nitrogenase activity in oligotrophic tailings during HOSbR. These results suggest that bacteria responsible for HOSbR may play various important ecological roles including reducing the mobility of Sb and improving nutrient conditions in oligotrophic habitats. Video Abstract.