Periphyton and Flocculent Materials Are Important Ecological Compartments Supporting Abundant and Diverse Mercury Methylator Assemblages in the Florida Everglades

Abstract

Methylmercury is a potent neurotoxin that impacts the health of humans and wildlife. Most mercury in wetlands such as the Florida Everglades enters as inorganic mercury via atmospheric deposition, some of which is transformed to the more toxic methylmercury through the activities of anaerobic microorganisms. We investigated the numbers and phylogenetic diversity of hgcAB , genes that are linked to mercury methylation, in the soil, floc, and periphyton in areas of the Everglades with different sulfate and nutrient concentrations. Soil harbored relatively high numbers of cells capable of methylating mercury; however, little detectable methylmercury was present in soil. The greatest concentrations of methylmercury were found in floc and periphyton. The dominant methylators in those compartments included methanogens and Syntrophobacteriales . This work provides significant insight into the microbial processes that control methylation and form the basis for accumulation through the food chain in this important environment.