title: Anaerobic Mercury Methylation and Demethylation by Geobacter bemidjiensis Bem.
abstract: Microbial methylation and demethylation are two competing processes controlling the net production and bioaccumulation of neurotoxic methylmercury (MeHg) in natural ecosystems. Although mercury (Hg) methylation by anaerobic microorganisms and demethylation by aerobic Hg-resistant bacteria have both been extensively studied, little attention has been given to MeHg degradation by anaerobic bacteria, particularly the iron-reducing bacterium Geobacter bemidjiensis Bem. Here we report, for the first time, that the strain G. bemidjiensis Bem can mediate a suite of Hg transformations, including Hg(II) reduction, Hg(0) oxidation, MeHg production and degradation under anoxic conditions. Results suggest that G. bemidjiensis utilizes a reductive demethylation pathway to degrade MeHg, with elemental Hg(0) as the major reaction product, possibly due to the presence of genes encoding homologues of an organomercurial lyase (MerB) and a mercuric reductase (MerA). In addition, the cells can strongly sorb Hg(II) and MeHg, reduce or oxidize Hg, resulting in both time and concentration-dependent Hg species transformations. Moderate concentrations (10-500 μM) of Hg-binding ligands such as cysteine enhance Hg(II) methylation but inhibit MeHg degradation. These findings indicate a cycle of Hg methylation and demethylation among anaerobic bacteria, thereby influencing net MeHg production in anoxic water and sediments.
authors.affiliation: School of Nuclear Science and Technology, Lanzhou University , Lanzhou, China.|Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Xia
authors.initials: X
authors.lastname: Lu
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing, China.
authors.forename: Yurong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Johs
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Linduo
authors.initials: L
authors.lastname: Zhao
authors.affiliation: School of Nuclear Science and Technology, Lanzhou University , Lanzhou, China.
authors.forename: Tieshan
authors.initials: T
authors.lastname: Wang
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Ziming
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Hui
authors.initials: H
authors.lastname: Lin
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Dwayne A
authors.initials: DA
authors.lastname: Elias
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Pierce
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Biology and Soft Matter Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Liyuan
authors.initials: L
authors.lastname: Liang
authors.affiliation: Department of Biochemistry and Microbiology, Rutgers University , New Brunswick, New Jersey 08901, United States.
authors.forename: Tamar
authors.initials: T
authors.lastname: Barkay
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Baohua
authors.initials: B
authors.lastname: Gu
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D003545:Cysteine / Q000737:chemistry; D004785:Environmental Pollutants / Q000737:chemistry / Q000378:metabolism*; D045302:Geobacter / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D008190:Lyases / Q000378:metabolism; D008628:Mercury / Q000737:chemistry / Q000378:metabolism*; D008745:Methylation; D008767:Methylmercury Compounds / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism
chemical_list: D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D007501:Iron; D010088:Oxidoreductases; C021551:mercuric reductase; D008190:Lyases; C050953:alkylmercury lyase; D008628:Mercury; D003545:Cysteine