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Title: Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments

Abstract

Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the genes hgcAB, but it is unknown how organic substrate and electron acceptor availability impacts the distribution and abundance of these organisms. We evaluated the impact of organic substrate amendments on mercury (Hg) methylation rates, microbial community structure, and the distribution of hgcAB + microbes with sediments. Sediment slurries were amended with short-chain fatty acids, alcohols, or a polysaccharide. Minimal increases in MeHg were observed following lactate, ethanol, and methanol amendments, while a significant decrease (~70%) was observed with cellobiose incubations. Postincubation, microbial diversity was assessed via 16S rRNA amplicon sequencing. The presence of hgcAB + organisms was assessed with a broad-range degenerate PCR primer set for both genes, while the presence of microbes in each of the three dominant clades of methylators (Deltaproteobacteria, Firmicutes, and methanogenic Archaea) was measured with clade-specific degenerate hgcA quantitative PCR (qPCR) primer sets. The predominant microorganisms in unamended sediments consisted of Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. Clade-specific qPCR identified hgcA + Deltaproteobacteria and Archaea in all sites but failed to detect hgcA + Firmicutes. Cellobiose shifted the communities in all samples to ~90% non-hgcAB-containing Firmicutes (mainly Bacillus spp. and Clostridium spp.). These resultsmore » suggest that either expression of hgcAB is downregulated or, more likely given the lack of 16S rRNA gene presence after cellobiose incubation, Hg-methylating organisms are largely outcompeted by cellobiose degraders or degradation products of cellobiose. These results represent a step toward understanding and exploring simple methodologies for controlling MeHg production in the environment. Methylmercury (MeHg) is a neurotoxin produced by microorganisms that bioacummulates in the food web and poses a serious health risk to humans. Currently, the impact that organic substrate or electron acceptor availability has on the mercury (Hg)-methylating microorganisms is unclear. To study this, we set up microcosm experiments exposed to different organic substrates and electron acceptors and assayed for Hg methylation rates, for microbial community structure, and for distribution of Hg methylators. The sediment and groundwater was collected from East Fork Poplar Creek in Oak Ridge, TN. Amendment with cellobiose (a lignocellulosic degradation by-product) led to a drastic decrease in the Hg methylation rate compared to that in an unamended control, with an associated shift in the microbial community to mostly nonmethylating Firmicutes. This, along with previous Hg-methylating microorganism identification methods, will be important for identifying strategies to control MeHg production and inform future remediation strategies.« less

Authors:
 [1];  [2];  [3];  [4];  [1];  [5];  [1];  [1];  [1];  [6];  [1];  [7]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Texas A & M Univ., Overton, TX (United States). Dept. of Soil and Crop Sciences
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Univ. of Idaho, Moscow, ID (United States). Dept. of Chemical and Materials Engineering
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Troy Univ., AL (United States). Dept. of Biology
  5. Smithsonian Environmental Research Center, Edgewater, MD (United States)
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division
  7. Univ. of Missouri, Columbia, MO (United States). Dept. of Biochemistry
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1423062
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Applied and Environmental Microbiology
Additional Journal Information:
Journal Volume: 84; Journal Issue: 3; Journal ID: ISSN 0099-2240
Publisher:
American Society for Microbiology
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 54 ENVIRONMENTAL SCIENCES; methylmercury; 16S; qPCR; hgcA; hgcAB; mercury

Citation Formats

Christensen, Geoff A., Somenahally, Anil C., Moberly, James G., Miller, Carrie M., King, Andrew J., Gilmour, Cynthia C., Brown, Steven D., Podar, Mircea, Brandt, Craig C., Brooks, Scott C., Palumbo, Anthony V., Wall, Judy D., and Elias, Dwayne A. Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments. United States: N. p., 2017. Web. doi:10.1128/AEM.01049-17.
Christensen, Geoff A., Somenahally, Anil C., Moberly, James G., Miller, Carrie M., King, Andrew J., Gilmour, Cynthia C., Brown, Steven D., Podar, Mircea, Brandt, Craig C., Brooks, Scott C., Palumbo, Anthony V., Wall, Judy D., & Elias, Dwayne A. Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments. United States. doi:10.1128/AEM.01049-17.
Christensen, Geoff A., Somenahally, Anil C., Moberly, James G., Miller, Carrie M., King, Andrew J., Gilmour, Cynthia C., Brown, Steven D., Podar, Mircea, Brandt, Craig C., Brooks, Scott C., Palumbo, Anthony V., Wall, Judy D., and Elias, Dwayne A. Fri . "Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments". United States. doi:10.1128/AEM.01049-17. https://www.osti.gov/servlets/purl/1423062.
@article{osti_1423062,
title = {Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments},
author = {Christensen, Geoff A. and Somenahally, Anil C. and Moberly, James G. and Miller, Carrie M. and King, Andrew J. and Gilmour, Cynthia C. and Brown, Steven D. and Podar, Mircea and Brandt, Craig C. and Brooks, Scott C. and Palumbo, Anthony V. and Wall, Judy D. and Elias, Dwayne A.},
abstractNote = {Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the genes hgcAB, but it is unknown how organic substrate and electron acceptor availability impacts the distribution and abundance of these organisms. We evaluated the impact of organic substrate amendments on mercury (Hg) methylation rates, microbial community structure, and the distribution of hgcAB+ microbes with sediments. Sediment slurries were amended with short-chain fatty acids, alcohols, or a polysaccharide. Minimal increases in MeHg were observed following lactate, ethanol, and methanol amendments, while a significant decrease (~70%) was observed with cellobiose incubations. Postincubation, microbial diversity was assessed via 16S rRNA amplicon sequencing. The presence of hgcAB+ organisms was assessed with a broad-range degenerate PCR primer set for both genes, while the presence of microbes in each of the three dominant clades of methylators (Deltaproteobacteria, Firmicutes, and methanogenic Archaea) was measured with clade-specific degenerate hgcA quantitative PCR (qPCR) primer sets. The predominant microorganisms in unamended sediments consisted of Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. Clade-specific qPCR identified hgcA+ Deltaproteobacteria and Archaea in all sites but failed to detect hgcA+ Firmicutes. Cellobiose shifted the communities in all samples to ~90% non-hgcAB-containing Firmicutes (mainly Bacillus spp. and Clostridium spp.). These results suggest that either expression of hgcAB is downregulated or, more likely given the lack of 16S rRNA gene presence after cellobiose incubation, Hg-methylating organisms are largely outcompeted by cellobiose degraders or degradation products of cellobiose. These results represent a step toward understanding and exploring simple methodologies for controlling MeHg production in the environment. Methylmercury (MeHg) is a neurotoxin produced by microorganisms that bioacummulates in the food web and poses a serious health risk to humans. Currently, the impact that organic substrate or electron acceptor availability has on the mercury (Hg)-methylating microorganisms is unclear. To study this, we set up microcosm experiments exposed to different organic substrates and electron acceptors and assayed for Hg methylation rates, for microbial community structure, and for distribution of Hg methylators. The sediment and groundwater was collected from East Fork Poplar Creek in Oak Ridge, TN. Amendment with cellobiose (a lignocellulosic degradation by-product) led to a drastic decrease in the Hg methylation rate compared to that in an unamended control, with an associated shift in the microbial community to mostly nonmethylating Firmicutes. This, along with previous Hg-methylating microorganism identification methods, will be important for identifying strategies to control MeHg production and inform future remediation strategies.},
doi = {10.1128/AEM.01049-17},
journal = {Applied and Environmental Microbiology},
number = 3,
volume = 84,
place = {United States},
year = {2017},
month = {11}
}

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