Arsenite-oxidizing chemolithooautotrophic prokaryotes underpin inorganic carbon fixation and arsenic detoxification in deep underground uranium mining layers

Abstract

Acid in-situ leach uranium (U) mining layers (ML) characterized by anaerobic, oligotrophic conditions, high arsenic (As) concentration, represent an unique but poorly characterized microbial habitat. Herein, autotrophic microbial metabolisms and arsenic detoxification strategies in underground ML (depth >111 m) were revealed through 16S rRNA gene amplicon sequencing and metagenomic analysis. Dissolved organic matter (DOM) content in ML after acid in-situ leach mining was significantly higher than that in non-mining layers (NML). Compared with NML, the arsenite (As(III)) content in ML showed a decreasing trend, while the As(V) content correspondingly increased significantly. As(III) and DOM showed significant positive effects on the diversity of bacterial communities in ML and NML. The genes involved in Calvin Benson Bassham (CBB) pathway and monosaccharide decomposition dominated the DOM dynamics in ML and NML. Notably, metabolic pathway analyses demonstrated that microbial As(III) anaerobic oxidation by coupling with nitrate reduction favors CO₂ fixation driven by CBB pathway, reducing As toxicity and enhancing DOM content in ML. Chemolithoautotrophs utilize multiple survival strategies (e.g., nitrate assimilation, metals efflux) in ML. These findings reveal that chemolithoautotropic microbial As(III) oxidation contributes to CO₂ fixation and As detoxification in ML, broadening our horizons of As and carbon cycling in deep underground mining environments.