title: Mercury methylation by novel microorganisms from new environments.
abstract: Microbial mercury (Hg) methylation transforms a toxic trace metal into the highly bioaccumulated neurotoxin methylmercury (MeHg). The lack of a genetic marker for microbial MeHg production has prevented a clear understanding of Hg-methylating organism distribution in nature. Recently, a specific gene cluster (hgcAB) was linked to Hg methylation in two bacteria.1 Here we test if the presence of hgcAB orthologues is a reliable predictor of Hg methylation capability in microorganisms, a necessary confirmation for the development of molecular probes for Hg-methylation in nature. Although hgcAB orthologues are rare among all available microbial genomes, organisms are much more phylogenetically and environmentally diverse than previously thought. By directly measuring MeHg production in several bacterial and archaeal strains encoding hgcAB, we confirmed that possessing hgcAB predicts Hg methylation capability. For the first time, we demonstrated Hg methylation in a number of species other than sulfate- (SRB) and iron- (FeRB) reducing bacteria, including methanogens, and syntrophic, acetogenic, and fermentative Firmicutes. Several of these species occupy novel environmental niches for Hg methylation, including methanogenic habitats such as rice paddies, the animal gut, and extremes of pH and salinity. Identification of these organisms as Hg methylators now links methylation to discrete gene markers in microbial communities.
authors.affiliation: Smithsonian Environmental Research Center , Edgewater, Maryland, United States.
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Gilmour
authors.forename: Mircea
authors.initials: M
authors.lastname: Podar
authors.forename: Allyson L
authors.initials: AL
authors.lastname: Bullock
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Graham
authors.forename: Steven D
authors.initials: SD
authors.lastname: Brown
authors.forename: Anil C
authors.initials: AC
authors.lastname: Somenahally
authors.forename: Alex
authors.initials: A
authors.lastname: Johs
authors.forename: Richard A
authors.initials: RA
authors.lastname: Hurt
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Bailey
authors.forename: Dwayne A
authors.initials: DA
authors.lastname: Elias
mesh_terms: D001419:Bacteria / Q000254:growth & development / Q000378:metabolism*; D061249:Batch Cell Culture Techniques; D001673:Biodegradation, Environmental; D044822:Biodiversity; D017753:Ecosystem; D004783:Environmental Microbiology; D005798:Genes, Bacterial; D008628:Mercury / Q000378:metabolism*; D008745:Methylation; D005810:Multigene Family; D010802:Phylogeny; D013045:Species Specificity
chemical_list: D008628:Mercury