Title: Anaerobic Mercury Methylation and Demethylation by Geobacter bemidjiensis Bem

Abstract

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:

Lu, Xia ^[1]; Liu, Yurong ^[2]; Johs, Alexander ^[3]; Zhao, Linduo ^[3]; Wang, Tieshan ^[4]; Yang, Ziming ^[3]; Lin, Hui ^[3]; Elias, Dwayne A. ^[5]; Pierce, Eric M. ^[3]; Liang, Liyuan ^[6]; Barkay, Tamar ^[7]; Gu, Baohua ^[3]

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+ Show Author Affiliations

1. School of Nuclear Science and Technology, Lanzhou University, Lanzhou, China, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
2. 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
3. Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
4. School of Nuclear Science and Technology, Lanzhou University, Lanzhou, China
5. Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
6. 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
7. Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey 08901, United States

Publication Date:

Thu Apr 07 00:00:00 EDT 2016

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1245891

Alternate Identifier(s):

OSTI ID: 1319176

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Published Article

Journal Name:

Environmental Science and Technology

Additional Journal Information:

Journal Name: Environmental Science and Technology Journal Volume: 50 Journal Issue: 8; Journal ID: ISSN 0013-936X

Publisher:

American Chemical Society

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