Aquifer Microbial Communities Differentially Display Metabolisms Capable of Secondary Effects on Uranium Speciation Across a Former Metal Processing Site.

Groundwater contamination presents worldwide challenges, yet remediation solutions in variably oxidized regions are limited, with co-interactions between contaminant metals and microbial reactions occurring. Here we present a genomic and metabolic study into the biogeochemistry of a uranium-contaminated surficial aquifer site in Riverton, WY. We identified unique communities that varied based on geochemistry, geography, and compartment, matching other microbial subsurface studies. Cross-site metabolism tests showed communities had functional capabilities of nitrogen respiration, manganese reduction, iron reduction, and sulfide oxidation. None of the sites displayed evidence of direct U-bioreduction nor ammonium oxidation. Only former tailings area sites nearest a retention pond and a downgradient oxbow lake exhibited sulfate reduction metabolisms. This was contrary to our hypothesis of near-river downgradient groundwater sites having U and S reduction capability. Most communities which showed S reduction capacity exhibited Fe oxidation capacity. Modelling demonstrated U as calcium uranyl carbonates. Based on our metabolism tests and known mineral and microbial metabolism reduction potentials, this suggests U reduction could be achieved via a secondary reaction with biogenically-formed sulfide. Of 11 sites tested, this is possible in four. Microbial metabolisms were analysed for capacity to influence U reduction-oxidation and provide microbial context to site remediation enhanced flushing efforts.