Microbially-mediated Mercury Cycling


Mercury contamination of sediments is still persistent in US Department of Energy (DOE) sites, such as the Savannah River site (SRS, SC) and Oak Ridge Reservation (ORR, TN). All species of mercury are developmental and neurotoxins. Monomethyl Hg (MeHg) biomagnifies through food webs, and is the most significant toxic species in environmental exposures. Sulfate reducing bacteria are recognized as major contributors to MeHg production, but several other anaerobic microorganisms, such as some methanogens, iron reducing bacteria, and the syntrophic, acetogenic and fermentative Firmicutes have also been reported to methylate Hg.

One major degradation mechanism for MeHg is microbially-mediated demethylation, which is poorly understood. To further understand the environmental, biogeochemical and microbial mechanisms regulating Hg methylation and demethylation at two Hg-impacted DOE facilities, PI and Co-PIs at FAMU (an HBCU), and Co-PIs from Oak Ridge National Lab (ORNL), Savannah River Ecology Lab (SREL) and Louisiana State University (LSU) will jointly evaluate microbially-mediated mercury (Hg) cycling processes at the Oak Ridge Reservation (ORR), TN and the Savannah River Site (SRS), SC.

Specifically, we will compare mercury contaminated and un-contaminated sediments, collected across different seasons, from ORR and SRS sediment samples to: 1) optimize whole cell bacterial bioreporter strain(s) to measure Hg bioavailability; 2) evaluate relationships among  total Hg, bioavailable Hg, methylmercury, soil nutrients and gene copy numbers of Hg methylation (hgcAB) and demethylation (merAB); 3) conduct metagenomic, metatranscriptomic and metaproteomic analyses to evaluate impacts to the soil microbiome and associated functions from Hg-contamination; and 4) use interdisciplinary and intertwined research-based pedagogy to train a steady stream of under-represented undergraduate and graduate students in environmental sciences for possible recruitment into DOE’s technical and scientific workforce.