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Lin H, Ascher DB, Myung Y, Lamborg CH, Hallam SJ, Gionfriddo CM, Holt KE, Moreau JW. Mercury methylation by metabolically versatile and cosmopolitan marine bacteria. THE ISME JOURNAL 2021; 15:1810-1825. [PMID: 33504941 DOI: 10.1101/2020.06.03.132969] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 12/17/2020] [Indexed: 05/21/2023]
Abstract
Microbes transform aqueous mercury (Hg) into methylmercury (MeHg), a potent neurotoxin that accumulates in terrestrial and marine food webs, with potential impacts on human health. This process requires the gene pair hgcAB, which encodes for proteins that actuate Hg methylation, and has been well described for anoxic environments. However, recent studies report potential MeHg formation in suboxic seawater, although the microorganisms involved remain poorly understood. In this study, we conducted large-scale multi-omic analyses to search for putative microbial Hg methylators along defined redox gradients in Saanich Inlet, British Columbia, a model natural ecosystem with previously measured Hg and MeHg concentration profiles. Analysis of gene expression profiles along the redoxcline identified several putative Hg methylating microbial groups, including Calditrichaeota, SAR324 and Marinimicrobia, with the last the most active based on hgc transcription levels. Marinimicrobia hgc genes were identified from multiple publicly available marine metagenomes, consistent with a potential key role in marine Hg methylation. Computational homology modelling predicts that Marinimicrobia HgcAB proteins contain the highly conserved amino acid sites and folding structures required for functional Hg methylation. Furthermore, a number of terminal oxidases from aerobic respiratory chains were associated with several putative novel Hg methylators. Our findings thus reveal potential novel marine Hg-methylating microorganisms with a greater oxygen tolerance and broader habitat range than previously recognized.
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Affiliation(s)
- Heyu Lin
- School of Earth Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - David B Ascher
- Structural Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, VIC, 3010, Australia
- Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, PO Box 6492, Melbourne, VIC, 3004, Australia
| | - Yoochan Myung
- Structural Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, VIC, 3010, Australia
- Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, PO Box 6492, Melbourne, VIC, 3004, Australia
| | - Carl H Lamborg
- Department of Ocean Sciences, University of California, Santa Cruz, CA, 95064, USA
| | - Steven J Hallam
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
- Genome Science and Technology Program, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Caitlin M Gionfriddo
- Biosciences Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN, 37831, USA
- Smithsonian Environmental Research Center, Edgewater, MD, 21037, USA
| | - Kathryn E Holt
- Department of Infectious Diseases, Central Clinical School, Monash University, Monash, VIC, 3800, Australia
- Department of Infection Biology, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
| | - John W Moreau
- School of Earth Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia.
- Currently at School of Geographical & Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
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Lin H, Ascher DB, Myung Y, Lamborg CH, Hallam SJ, Gionfriddo CM, Holt KE, Moreau JW. Mercury methylation by metabolically versatile and cosmopolitan marine bacteria. THE ISME JOURNAL 2021; 15:1810-1825. [PMID: 33504941 PMCID: PMC8163782 DOI: 10.1038/s41396-020-00889-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 12/17/2020] [Indexed: 01/30/2023]
Abstract
Microbes transform aqueous mercury (Hg) into methylmercury (MeHg), a potent neurotoxin that accumulates in terrestrial and marine food webs, with potential impacts on human health. This process requires the gene pair hgcAB, which encodes for proteins that actuate Hg methylation, and has been well described for anoxic environments. However, recent studies report potential MeHg formation in suboxic seawater, although the microorganisms involved remain poorly understood. In this study, we conducted large-scale multi-omic analyses to search for putative microbial Hg methylators along defined redox gradients in Saanich Inlet, British Columbia, a model natural ecosystem with previously measured Hg and MeHg concentration profiles. Analysis of gene expression profiles along the redoxcline identified several putative Hg methylating microbial groups, including Calditrichaeota, SAR324 and Marinimicrobia, with the last the most active based on hgc transcription levels. Marinimicrobia hgc genes were identified from multiple publicly available marine metagenomes, consistent with a potential key role in marine Hg methylation. Computational homology modelling predicts that Marinimicrobia HgcAB proteins contain the highly conserved amino acid sites and folding structures required for functional Hg methylation. Furthermore, a number of terminal oxidases from aerobic respiratory chains were associated with several putative novel Hg methylators. Our findings thus reveal potential novel marine Hg-methylating microorganisms with a greater oxygen tolerance and broader habitat range than previously recognized.
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Affiliation(s)
- Heyu Lin
- grid.1008.90000 0001 2179 088XSchool of Earth Sciences, The University of Melbourne, Parkville, VIC 3010 Australia
| | - David B. Ascher
- grid.1008.90000 0001 2179 088XStructural Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, VIC 3010 Australia ,grid.1051.50000 0000 9760 5620Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, PO Box 6492, Melbourne, VIC 3004 Australia
| | - Yoochan Myung
- grid.1008.90000 0001 2179 088XStructural Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, VIC 3010 Australia ,grid.1051.50000 0000 9760 5620Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, PO Box 6492, Melbourne, VIC 3004 Australia
| | - Carl H. Lamborg
- grid.205975.c0000 0001 0740 6917Department of Ocean Sciences, University of California, Santa Cruz, CA 95064 USA
| | - Steven J. Hallam
- grid.17091.3e0000 0001 2288 9830Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC V6T 1Z1 Canada ,grid.17091.3e0000 0001 2288 9830Genome Science and Technology Program, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
| | - Caitlin M. Gionfriddo
- grid.135519.a0000 0004 0446 2659Biosciences Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831 USA ,grid.419533.90000 0000 8612 0361Present Address: Smithsonian Environmental Research Center, Edgewater, MD 21037 USA
| | - Kathryn E. Holt
- grid.1002.30000 0004 1936 7857Department of Infectious Diseases, Central Clinical School, Monash University, Monash, VIC 3800 Australia ,grid.8991.90000 0004 0425 469XDepartment of Infection Biology, London School of Hygiene & Tropical Medicine, London, WC1E 7HT UK
| | - John W. Moreau
- grid.1008.90000 0001 2179 088XSchool of Earth Sciences, The University of Melbourne, Parkville, VIC 3010 Australia ,grid.8756.c0000 0001 2193 314XPresent Address: Currently at School of Geographical & Earth Sciences, University of Glasgow, Glasgow, G12 8QQ UK
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Swift evolutionary response of microbes to a rise in anthropogenic mercury in the Northern Hemisphere. ISME JOURNAL 2019; 14:788-800. [PMID: 31831837 PMCID: PMC7031220 DOI: 10.1038/s41396-019-0563-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 11/17/2019] [Indexed: 01/22/2023]
Abstract
Anthropogenic mercury remobilization has considerably increased since the Industrial Revolution in the late 1700s. The Minamata Convention on Mercury is a United Nations treaty (2017) aiming at curbing mercury emissions. Unfortunately, evaluating the effectiveness of such a global treaty is hampered by our inability to determine the lag in aquatic ecosystem responses to a change in atmospheric mercury deposition. Whereas past metal concentrations are obtained from core samples, there are currently no means of tracking historical metal bioavailability or toxicity. Here, we recovered DNA from nine dated sediment cores collected in Canada and Finland, and reconstructed the past demographics of microbes carrying genes coding for the mercuric reductase (MerA)—an enzyme involved in Hg detoxification—using Bayesian relaxed molecular clocks. We found that the evolutionary dynamics of merA exhibited a dramatic increase in effective population size starting from 1783.8 ± 3.9 CE, which coincides with both the Industrial Revolution, and with independent measurements of atmospheric Hg concentrations. We show that even low levels of anthropogenic mercury affected the evolutionary trajectory of microbes in the Northern Hemisphere, and that microbial DNA encoding for detoxification determinants stored in environmental archives can be used to track historical pollutant toxicity.
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Liu M, Chen L, He Y, Baumann Z, Mason RP, Shen H, Yu C, Zhang W, Zhang Q, Wang X. Impacts of farmed fish consumption and food trade on methylmercury exposure in China. ENVIRONMENT INTERNATIONAL 2018; 120:333-344. [PMID: 30114623 PMCID: PMC6174094 DOI: 10.1016/j.envint.2018.08.017] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 08/02/2018] [Accepted: 08/02/2018] [Indexed: 05/04/2023]
Abstract
The global pollutant mercury (Hg), especially as methylmercury (MeHg), threatens human and ecosystem health. But major contributors of MeHg exposure to people in China remain highly debated. We developed the China Mercury Exposure Assessment (CMEA) model, which incorporates human exposure pathways for MeHg and total Hg (THg), the interregional, including international and interprovincial, food trading as well as human physiology to provide a comprehensive system that can evaluate the pathway of Hg forms to human consumers in China. Based on the CMEA model that employed the most comprehensive and recent data, we have found that the Probable Daily Intake (PDI) of MeHg for the Chinese population was 0.057 (range: 0.036-0.091 as 60% confidence interval) μg·kg-1·day-1, while that of THg was 0.35 (range: 0.22-0.55) μg·kg-1·day-1. MeHg exposure was dominated by fish intake, especially by farm-raised freshwater fish due to higher consumption of these fish. In 2011, fish intake contributed to 56% to the total MeHg exposure, followed by rice (26%). Consumption of farm-raised fish reduced human exposure to MeHg by 33%. On the other hand, interregional food trading increased MeHg exposure of the Chinese population, as a whole, by 7.6%. The international and interprovincial food trades contributed to 5.1% and 22% of MeHg intake, respectively. For the whole China, fish intake related exposure to MeHg was highest for the Eastern and Northeastern populations, while Tibetans were chronically exposed to the highest MeHg from other sources. Our findings highlight the importance of farmed fish and food trade for MeHg exposure.
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Affiliation(s)
- Maodian Liu
- Ministry of Education Laboratory of Earth Surface Process, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China; Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, USA
| | - Long Chen
- Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai 200241, China; School of Geographic Sciences, East China Normal University, Shanghai 200241, China
| | - Yipeng He
- Ministry of Education Laboratory of Earth Surface Process, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China; Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, USA
| | - Zofia Baumann
- Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, USA
| | - Robert P Mason
- Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, USA
| | - Huizhong Shen
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Chenghao Yu
- Ministry of Education Laboratory of Earth Surface Process, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
| | - Wei Zhang
- School of Environment and Natural Resources, Renmin University of China, Beijing 100872, China
| | - Qianggong Zhang
- Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China; Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
| | - Xuejun Wang
- Ministry of Education Laboratory of Earth Surface Process, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
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