title: Global prevalence and distribution of genes and microorganisms involved in mercury methylation.
abstract: Mercury (Hg) methylation produces the neurotoxic, highly bioaccumulative methylmercury (MeHg). The highly conserved nature of the recently identified Hg methylation genes hgcAB provides a foundation for broadly evaluating spatial and niche-specific patterns of microbial Hg methylation potential in nature. We queried hgcAB diversity and distribution in >3500 publicly available microbial metagenomes, encompassing a broad range of environments and generating a new global view of Hg methylation potential. The hgcAB genes were found in nearly all anaerobic (but not aerobic) environments, including oxygenated layers of the open ocean. Critically, hgcAB was effectively absent in ~1500 human and mammalian microbiomes, suggesting a low risk of endogenous MeHg production. New potential methylation habitats were identified, including invertebrate digestive tracts, thawing permafrost soils, coastal "dead zones," soils, sediments, and extreme environments, suggesting multiple routes for MeHg entry into food webs. Several new taxonomic groups capable of methylating Hg emerged, including lineages having no cultured representatives. Phylogenetic analysis points to an evolutionary relationship between hgcA and genes encoding corrinoid iron-sulfur proteins functioning in the ancient Wood-Ljungdahl carbon fixation pathway, suggesting that methanogenic Archaea may have been the first to perform these biotransformations.
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Mircea
authors.initials: M
authors.lastname: Podar
authors.affiliation: Smithsonian Environmental Research Center, Edgewater, MD 21037-0028, USA.
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Gilmour
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Craig C
authors.initials: CC
authors.lastname: Brandt
authors.affiliation: Smithsonian Environmental Research Center, Edgewater, MD 21037-0028, USA.
authors.forename: Allyson
authors.initials: A
authors.lastname: Soren
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Brown
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Bryan R
authors.initials: BR
authors.lastname: Crable
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Anthony V
authors.initials: AV
authors.lastname: Palumbo
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. ; Department of Soil and Crop Sciences, Texas A&M University, Overton, TX 75684, USA.
authors.forename: Anil C
authors.initials: AC
authors.lastname: Somenahally
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Dwayne A
authors.initials: DA
authors.lastname: Elias
keywords: Mercury methylation; hgcAB; mercury; methylmercury; microbiology