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This content will become publicly available on March 28, 2017

Title: Anaerobic Mercury Methylation and Demethylation by Geobacter bemidjiensis Bem

Two competing processes controlling the net production and bioaccumulation of neurotoxic methylmercury (MeHg) in natural ecosystems are microbial methylation and demethylation. Though 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 bemidjensis Bem. Here we report, for the first time, that the strain G. bemidjensis Bem can methylate inorganic Hg and degrade MeHg concurrently under anoxic conditions. Our results suggest that G. bemidjensis cells utilize a reductive demethylation pathway to degrade MeHg, with elemental Hg(0) as the major reaction product, possibly due to the presence of homologs encoding both organo-mercurial lyase (MerB) and mercuric reductase (MerA) in this organism. In addition, the cells can mediate multiple reactions including Hg/MeHg sorption, Hg reduction and oxidation, resulting in both time and concentration dependent Hg species transformations. Moderate concentrations (10 500 M) of Hg-binding ligands such as cysteine enhance Hg(II) methylation but inhibit MeHg degradation. These findings indicate a cycle of methylation and demethylation among anaerobic bacteria and suggest that mer-mediated demethylation may play a role in the net balance of MeHg production in anoxic water and sediments.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [3] ;  [3] ;  [5] ;  [3] ;  [6] ;  [7] ;  [3]
  1. Lanzhou Univ. (China). School of Nuclear Science and Technology; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division; Chinese Academy of Sciences (CAS), Beijing (China)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division
  4. Lanzhou Univ. (China). School of Nuclear Science and Technology
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division and Biology and Soft Matter Division
  7. Rutgers Univ., New Brunswick, NJ (United States). Dept. of Biochemistry and Microbiology
Publication Date:
OSTI Identifier:
1319176
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 50; Journal Issue: 8; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES Mercury; methylmercury; demethylation; Geobacter bemidjensis; methylation