Abstract
In modern Earth, anaerobic pyrite oxidation under circumneutral conditions also has great impact on the fate of nitrate in aquifers and sediments, as well as the transportation of toxic metals. However, the mechanism of how microbes mediated this process is still being debated. Electrochemical analysis on pyrite cubic electrode showed that, its oxidation threshold under anaerobic circumneutral conditions (ca. 200 mV) was much lower than that at aerobic acidic conditions (ca. 650 mV), implying possible direct pyrite oxidation by high redox potential cellular components. Sole substrate (pyrite) microbial enrichment cultures with EDTA addition showed higher oxidation rate (0.092 d-1) than that of EDTA-free cultures (0.019 d-1), suggesting that ligands producing pathway was much preferred by microbes than maintaining acidic micro-environments. This hypothesis was supported by amplicon and metagenomic sequencing data, which demonstrated discrepant bacteria involving iron-sulfur oxidation and metabolic potentials in cultures with/without EDTA addition. A concept model was proposed based on experimental data considering different reaction stages and microbial communities. The results shed lights on the potential interactions between microbes and pyrite, which may serve as a model for explaining subsurface pyrite oxidation and optimizing anaerobic pyrite oxidation-based pollutant removal processes.
