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Boie F, Ducey TF, Xing Y, Wang J, Rinklebe J. Field-aged rice hull biochar stimulated the methylation of mercury and altered the microbial community in a paddy soil under controlled redox condition changes. JOURNAL OF HAZARDOUS MATERIALS 2024; 472:134446. [PMID: 38696958 DOI: 10.1016/j.jhazmat.2024.134446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 03/25/2024] [Accepted: 04/25/2024] [Indexed: 05/04/2024]
Abstract
Mercury (Hg) contaminated paddy soils are hot spots for methylmercury (MeHg) which can enter the food chain via rice plants causing high risks for human health. Biochar can immobilize Hg and reduce plant uptake of MeHg. However, the effects of biochar on the microbial community and Hg (de)methylation under dynamic redox conditions in paddy soils are unclear. Therefore, we determined the microbial community in an Hg contaminated paddy soil non-treated and treated with rice hull biochar under controlled redox conditions (< 0 mV to 600 mV) using a biogeochemical microcosm system. Hg methylation exceeded demethylation in the biochar-treated soil. The aromatic hydrocarbon degraders Phenylobacterium and Novosphingobium provided electron donors stimulating Hg methylation. MeHg demethylation exceeded methylation in the non-treated soil and was associated with lower available organic matter. Actinobacteria were involved in MeHg demethylation and interlinked with nitrifying bacteria and nitrogen-fixing genus Hyphomicrobium. Microbial assemblages seem more important than single species in Hg transformation. For future directions, the demethylation potential of Hyphomicrobium assemblages and other nitrogen-fixing bacteria should be elucidated. Additionally, different organic matter inputs on paddy soils under constant and dynamic redox conditions could unravel the relationship between Hg (de)methylation, microbial carbon utilization and nitrogen cycling.
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Affiliation(s)
- Felizitas Boie
- University of Wuppertal, School of Architecture and Civil Engineering, Institute of Foundation Engineering, Water and Waste Management, Laboratory of Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany
| | - Thomas F Ducey
- US Department of Agriculture, Coastal Plains Soil, Water, Plant Research Center, 2611 West Lucas Street, Florence, SC, USA
| | - Ying Xing
- University of Wuppertal, School of Architecture and Civil Engineering, Institute of Foundation Engineering, Water and Waste Management, Laboratory of Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany; School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550002, PR China
| | - Jianxu Wang
- University of Wuppertal, School of Architecture and Civil Engineering, Institute of Foundation Engineering, Water and Waste Management, Laboratory of Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany; State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 550082 Guiyang, P.R. China
| | - Jörg Rinklebe
- University of Wuppertal, School of Architecture and Civil Engineering, Institute of Foundation Engineering, Water and Waste Management, Laboratory of Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany.
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Wang YL, Ikuma K, Brown AMV, Deonarine A. Global survey of hgcA-carrying genomes in marine and freshwater sediments: Insights into mercury methylation processes. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 352:124117. [PMID: 38714231 DOI: 10.1016/j.envpol.2024.124117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 04/11/2024] [Accepted: 05/05/2024] [Indexed: 05/09/2024]
Abstract
Mercury (Hg) methylation is a microbially mediated process that produces methylmercury (MeHg), a bioaccumulative neurotoxin. A highly conserved gene pair, hgcAB, is required for Hg methylation, which provides a basis for identifying Hg methylators and evaluating their genomic composition. In this study, we conducted a large-scale omics analysis in which 281 metagenomic freshwater and marine sediment samples from 46 geographic locations across the globe were queried. Specific objectives were to examine the prevalence of Hg methylators, to identify horizontal gene transfer (HGT) events involving hgcAB within Hg methylator communities, and to identify associations between hgcAB and microbial biochemical functions/genes. Hg methylators from the phyla Desulfobacterota and Bacteroidota were dominant in both freshwater and marine sediments while Firmicutes and methanogens belonging to Euryarchaeota were identified only in freshwater sediments. Novel Hg methylators were found in the Phycisphaerae and Planctomycetia classes within the phylum Planctomycetota, including potential hgcA-carrying anammox metagenome-assembled genomes (MAGs) from Candidatus Brocadiia. HGT of hgcA and hgcB were identified in both freshwater and marine methylator communities. Spearman's correlation analysis of methylator genomes suggested that in addition to sulfide, thiosulfate, sulfite, and ammonia may be important parameters for Hg methylation processes in sediments. Overall, our results indicated that the biochemical drivers of Hg methylation vary between marine and freshwater sites, lending insight into the influence of environmental perturbances, such as a changing climate, on Hg methylation processes.
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Affiliation(s)
- Yong-Li Wang
- Department of Civil, Environmental & Construction Engineering, Texas Tech University, Lubbock, TX, United States
| | - Kaoru Ikuma
- Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA, United States
| | - Amanda M V Brown
- Department of Biological Sciences, Texas Tech University, Lubbock, TX, United States
| | - Amrika Deonarine
- Department of Civil, Environmental & Construction Engineering, Texas Tech University, Lubbock, TX, United States.
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Wang YL, Ikuma K, Brooks SC, Varonka MS, Deonarine A. Non-mercury methylating microbial taxa are integral to understanding links between mercury methylation and elemental cycles in marine and freshwater sediments. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 346:123573. [PMID: 38365074 DOI: 10.1016/j.envpol.2024.123573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 01/09/2024] [Accepted: 02/13/2024] [Indexed: 02/18/2024]
Abstract
The goal of this study was to explore the role of non-mercury (Hg) methylating taxa in mercury methylation and to identify potential links between elemental cycles and Hg methylation. Statistical approaches were utilized to investigate the microbial community and biochemical functions in relation to methylmercury (MeHg) concentrations in marine and freshwater sediments. Sediments were collected from the methylation zone (top 15 cm) in four Hg-contaminated sites. Both abiotic (e.g., sulfate, sulfide, iron, salinity, total organic matter, etc.) and biotic factors (e.g., hgcA, abundances of methylating and non-methylating taxa) were quantified. Random forest and stepwise regression were performed to assess whether non-methylating taxa were significantly associated with MeHg concentration. Co-occurrence and functional network analyses were constructed to explore associations between taxa by examining microbial community structure, composition, and biochemical functions across sites. Regression analysis showed that approximately 80% of the variability in sediment MeHg concentration was predicted by total mercury concentration, the abundances of Hg methylating taxa, and the abundances of the non-Hg methylating taxa. The co-occurrence networks identified Paludibacteraceae and Syntrophorhabdaceae as keystone non Hg methylating taxa in multiple sites, indicating the potential for syntrophic interactions with Hg methylators. Strong associations were also observed between methanogens and sulfate-reducing bacteria, which were likely symbiotic associations. The functional network results suggested that non-Hg methylating taxa play important roles in sulfur respiration, nitrogen respiration, and the carbon metabolism-related functions methylotrophy, methanotrophy, and chemoheterotrophy. Interestingly, keystone functions varied by site and did not involve carbon- and sulfur-related functions only. Our findings highlight associations between methylating and non-methylating taxa and sulfur, carbon, and nitrogen cycles in sediment methylation zones, with implications for predicting and understanding the impact of climate and land/sea use changes on Hg methylation.
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Affiliation(s)
- Yong-Li Wang
- Department of Civil, Environmental & Construction Engineering, Texas Tech University, Lubbock, TX, United States
| | - Kaoru Ikuma
- Department of Civil, Construction & Environmental Engineering, Iowa State University, Ames, IA, United States
| | - Scott C Brooks
- Oak Ridge National Laboratory, Environmental Science Division, Oak Ridge, TN, United States
| | - Matthew S Varonka
- U.S. Geological Survey, Geology, Energy & Minerals Science Center, Reston, VA, United States
| | - Amrika Deonarine
- Department of Civil, Environmental & Construction Engineering, Texas Tech University, Lubbock, TX, United States.
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Cabrol L, Capo E, van Vliet DM, von Meijenfeldt FAB, Bertilsson S, Villanueva L, Sánchez-Andrea I, Björn E, G. Bravo A, Heimburger Boavida LE. Redox gradient shapes the abundance and diversity of mercury-methylating microorganisms along the water column of the Black Sea. mSystems 2023; 8:e0053723. [PMID: 37578240 PMCID: PMC10469668 DOI: 10.1128/msystems.00537-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Accepted: 06/16/2023] [Indexed: 08/15/2023] Open
Abstract
In the global context of seawater deoxygenation triggered by climate change and anthropogenic activities, changes in redox gradients impacting biogeochemical transformations of pollutants, such as mercury, become more likely. Being the largest anoxic basin worldwide, with high concentrations of the potent neurotoxic methylmercury (MeHg), the Black Sea is an ideal natural laboratory to provide new insights about the link between dissolved oxygen concentration and hgcAB gene-carrying (hgc+) microorganisms involved in the formation of MeHg. We combined geochemical and microbial approaches to assess the effect of vertical redox gradients on abundance, diversity, and metabolic potential of hgc+ microorganisms in the Black Sea water column. The abundance of hgcA genes [congruently estimated by quantitative PCR (qPCR) and metagenomics] correlated with MeHg concentration, both maximal in the upper part of the anoxic water. Besides the predominant Desulfobacterales, hgc+ microorganisms belonged to a unique assemblage of diverse-previously underappreciated-anaerobic fermenters from Anaerolineales, Phycisphaerae (characteristic of the anoxic and sulfidic zone), Kiritimatiellales, and Bacteroidales (characteristic of the suboxic zone). The metabolic versatility of Desulfobacterota differed from strict sulfate reduction in the anoxic water to reduction of various electron acceptors in the suboxic water. Linking microbial activity and contaminant concentration in environmental studies is rare due to the complexity of biological pathways. In this study, we disentangle the role of oxygen in shaping the distribution of Hg-methylating microorganisms consistently with MeHg concentration, and we highlight their taxonomic and metabolic niche partitioning across redox gradients, improving the prediction of the response of marine communities to the expansion of oxygen-deficient zones. IMPORTANCE Methylmercury (MeHg) is a neurotoxin detected at high concentrations in certain marine ecosystems, posing a threat to human health. MeHg production is mainly mediated by hgcAB gene-carrying (hgc+) microorganisms. Oxygen is one of the main factors controlling Hg methylation; however, its effect on the diversity and ecology of hgc+ microorganisms remains unknown. Under the current context of seawater deoxygenation, mercury cycling is expected to be disturbed. Here, we show the strong effect of oxygen gradients on the distribution of potential Hg methylators. In addition, we show for the first time the significant contribution of a unique assemblage of potential fermenters from Anaerolineales, Phycisphaerae, and Kiritimatiellales to Hg methylation, stratified in different redox niches along the Black Sea gradient. Our results considerably expand the known taxonomic diversity and ecological niches prone to the formation of MeHg and contribute to better apprehend the consequences of oxygen depletion in seawater.
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Affiliation(s)
- Léa Cabrol
- Aix Marseille University, Univ. Toulon, CNRS, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, Marseille, France
- Institute of Ecology and Biodiversity (IEB), University of Chile, Santiago, Chile
| | - Eric Capo
- Department of Marine Biology and Oceanography, Institute of Marine Sciences, CSIC, Barcelona, Spain
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
- Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
| | - Daan M. van Vliet
- Laboratory of Microbiology, Wageningen University and Research, Wageningen, the Netherlands
- Wageningen Food and Biobased Research, Wageningen, the Netherlands
| | - F. A. Bastiaan von Meijenfeldt
- Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Texel, the Netherlands
| | - Stefan Bertilsson
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Laura Villanueva
- Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Texel, the Netherlands
- Faculty of Geosciences, Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands
| | - Irene Sánchez-Andrea
- Laboratory of Microbiology, Wageningen University and Research, Wageningen, the Netherlands
| | - Erik Björn
- Department of Chemistry, Umeå University, Umeå, Sweden
| | - Andrea G. Bravo
- Department of Marine Biology and Oceanography, Institute of Marine Sciences, CSIC, Barcelona, Spain
| | - Lars-Eric Heimburger Boavida
- Aix Marseille University, Univ. Toulon, CNRS, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, Marseille, France
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Wang T, Yang X, Li Z, Chen W, Wen X, He Y, Ma C, Yang Z, Zhang C. MeHg production in eutrophic lakes: Focusing on the roles of algal organic matter and iron-sulfur-phosphorus dynamics. JOURNAL OF HAZARDOUS MATERIALS 2023; 457:131682. [PMID: 37270963 DOI: 10.1016/j.jhazmat.2023.131682] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 05/20/2023] [Accepted: 05/21/2023] [Indexed: 06/06/2023]
Abstract
The mechanisms by which eutrophication affects methylmercury (MeHg) production have not been comprehensively summarized, which hinders accurately predicting the MeHg risk in eutrophic lakes. In this review, we first discussed the effects of eutrophication on biogeochemical cycle of mercury (Hg). Special attentions were paid to the roles of algal organic matter (AOM) and iron (Fe)-sulfur (S)-phosphorus (P) dynamics in MeHg production. Finally, the suggestions for risk control of MeHg in eutrophic lakes were proposed. AOM can affect in situ Hg methylation by stimulating the abundance and activities of Hg methylating microorganisms and regulating Hg bioavailability, which are dependent on bacteria-strain and algae species, the molecular weight and composition of AOM as well as environmental conditions (e.g., light). Fe-S-P dynamics under eutrophication including sulfate reduction, FeS formation and P release could also play crucial but complicated roles in MeHg production, in which AOM may participate through influencing the dissolution and aggregation processes, structural order and surface properties of HgS nanoparticles (HgSNP). Future studies should pay more attention to the dynamics of AOM in responses to the changing environmental conditions (e.g., light penetration and redox fluctuations) and how such variations will subsequently affect MeHg production. The effects of Fe-S-P dynamics on MeHg production under eutrophication also deserve further investigations, especially the interactions between AOM and HgSNP. Remediation strategies with lower disturbance, greater stability and less cost like the technology of interfacial O2 nanobubbles are urgent to be explored. This review will deepen our understanding of the mechanisms of MeHg production in eutrophic lakes and provide theoretical guidance for its risk control.
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Affiliation(s)
- Tantan Wang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Xu Yang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Zihao Li
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Wenhao Chen
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Xin Wen
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Yubo He
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Chi Ma
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Zhongzhu Yang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Chang Zhang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China.
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Zhu C, Lv S, Zhao Q, Liu X, Wang Z, Zheng X, Zhou L, Wang Y. Seasonal variation in mercury and methylmercury production in vegetated sediment in the Dongtan wetlands of the Yangtze River Estuary, China. MARINE ENVIRONMENTAL RESEARCH 2023; 188:105999. [PMID: 37182325 DOI: 10.1016/j.marenvres.2023.105999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 04/13/2023] [Accepted: 04/18/2023] [Indexed: 05/16/2023]
Abstract
The seasonal cycling of mercury (Hg) in vegetated sediments in the Dongtan wetlands of the Yangtze River Estuary were determined, and microcosm incubation experiments were conducted to evaluate methylmercury (MeHg) production after Hg input. The results showed that the seasonal variations of total Hg and MeHg were very different. The enhanced activity of methylating bacteria could have been the main contributor to the elevated MeHg in the upper surface layer (0-12 cm), which was supported by the higher copy numbers of the hgcA gene in the surface sediment and the MeHg increase during sediment incubation following litterfall addition. Moreover, the incubation results showed that Hg addition greatly increased net MeHg production and that this increase remained under suboxic conditions, suggesting that the potential health risk of Hg in estuarine wetlands could exist for a long time under changing redox conditions.
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Affiliation(s)
- Changle Zhu
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Shaoyang Lv
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Qing Zhao
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Xia Liu
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China; Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai, 200241, PR China
| | - Zhigang Wang
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Xiangmin Zheng
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China; Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai, 200241, PR China
| | - Limin Zhou
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China; Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai, 200241, PR China; Institute of Eco-Chongming, East China Normal University, Shanghai, 200241, PR China
| | - Yongjie Wang
- School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China; Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai, 200241, PR China.
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Schwartz GE, Muller KA, Rathore SS, Wilpiszeski RL, Carrell AA, Cregger MA, Elias DA, Podar M, Painter SL, Brooks SC. Incorporating concentration-dependent sediment microbial activity into methylmercury production kinetics modeling. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2022; 24:1392-1405. [PMID: 34727150 DOI: 10.1039/d1em00287b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In anoxic environments, anaerobic microorganisms carrying the hgcAB gene cluster can mediate the transformation of inorganic mercury (Hg(II)) to monomethylmercury (MMHg). The kinetics of Hg(II) transformation to MMHg in periphyton from East Fork Poplar Creek (EFPC) in Oak Ridge, TN have previously been modeled using a transient availability model (TAM). The TAM for Hg(II) methylation combines methylation/demethylation kinetics with kinetic expressions for processes that decrease Hg(II) and MMHg availability for methylation and demethylation (multisite sorption of Hg(II) and MMHg, Hg(II) reduction/Hg(0) oxidation). In this study, the TAM is used for the first time to describe MMHg production in sediment. We assessed MMHg production in sediment microcosms using two different sediment types from EFPC: a relatively anoxic, carbon-rich sediment with higher microbial activity (higher CO2 production from sediment) and a relatively oxic, sandy, carbon-poor sediment with lower microbial activity (lower CO2 production from sediment). Based on 16s rRNA sequencing, the overall microbial community structure in the two sediments was retained during the incubations. However, the hgcA containing methanogenic Euryarchaeota communities differed between sediment types and their growth followed different trajectories over the course of incubations, potentially contributing to the distinct patterns of MMHg production observed. The general TAM paradigm performed well in describing MMHg production in the sediments. However, the MMHg production and ancillary data suggested the need to revise the model structure to incorporate terms for concentration-dependent microbial activity over the course of the incubations. We modified the TAM to include Monod-type kinetics for methylation and demethylation and observed an improved fit for the carbon-rich, microbially active sediment. Overall our work shows that the TAM can be applied to describe Hg(II) methylation in sediments and that including expressions accounting for concentration-dependent microbial activity can improve the accuracy of the model description of the data in some cases.
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Affiliation(s)
- Grace E Schwartz
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
| | - Katherine A Muller
- Earth Systems Science Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Saubhagya S Rathore
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
| | - Regina L Wilpiszeski
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Alyssa A Carrell
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Melissa A Cregger
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Dwayne A Elias
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Mircea Podar
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Scott L Painter
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
| | - Scott C Brooks
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
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Bailon MX, Chaudhary DK, Jeon C, Ok YS, Hong Y. Impact of sulfur-impregnated biochar amendment on microbial communities and mercury methylation in contaminated sediment. JOURNAL OF HAZARDOUS MATERIALS 2022; 438:129464. [PMID: 35999716 DOI: 10.1016/j.jhazmat.2022.129464] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2022] [Revised: 06/16/2022] [Accepted: 06/24/2022] [Indexed: 06/15/2023]
Abstract
S-impregnation of biochar through elemental S streaming is known to increase its sorption performance against Hg and methyl mercury (MeHg). However, the effects of %S-loading on biochar's mechanism and sorption capacities for MeHg, and its consequent impact when used as an amendment material for Hg-contaminated sediments, are poorly understood, and thus, were investigated in this work. Our results showed that a minimum sulfur loading of 1% was the most effective in reducing MeHg levels in sediments. At higher %S-loading (3-20%), the reduction in surface area, pore blockage due to unreacted sulfur particles, and presence of poorly bound sulfur species resulted in lowered effectiveness for MeHg control. Increasing S-functionalization during impregnation shifted the sorption process of MeHg from Hg-O to Hg-S in S-impregnated biochar (BCS). Our 60-day slurry experiment showed a significant reduction in pore water THg (40-70%) and MeHg (30-55%), as well as sediment MeHg (50-60%) in biochar-amended sediments. The reduction in the bioavailable Hg resulted in lowered Hg methylation, as supported by the suppression of both the Fe- and SO42--reduction activities in the amended sediments. The microbial community structure in BCS-amended sediments showed a shift towards sulfur-consuming, iron-reducing, thiosulfate-oxidizing, and sulfate-reducing bacterial populations. At the genus level, the overall relative abundance of principal Hg methylators was also lower in the BCS treatment than in the unamended sediments. This study highlights the application of BCS as a promising strategy for remediation of Hg-contaminated sediments.
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Affiliation(s)
- Mark Xavier Bailon
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City 30019, South Korea; Department of Science and Technology - Philippines, Philippine Science High School - Central Luzon Campus, Lily Hill, Clark Freeport Zone, Mabalacat City, Pampanga 2010, Philippines
| | - Dhiraj Kumar Chaudhary
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City 30019, South Korea
| | - Cheolho Jeon
- Research Center for Materials Analysis, Korea Basic Science Institute, Daejeon, South Korea
| | - Yong Sik Ok
- Korea Biochar Research Center, APRU Sustainable Waste Management Program & Division of Environmental Science and Ecological Engineering, Korea University, Seoul, South Korea
| | - Yongseok Hong
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City 30019, South Korea.
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9
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Chaudhary DK, Kim H, Reible D, Lee M, Kim S, Kim LH, Kim S, Hong Y. Seasonal trends of mercury bioaccumulation and assessment of toxic effects in Asian clams and microbial community from field study of estuarine sediment. ENVIRONMENTAL RESEARCH 2022; 212:113439. [PMID: 35537496 DOI: 10.1016/j.envres.2022.113439] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 04/22/2022] [Accepted: 05/04/2022] [Indexed: 06/14/2023]
Abstract
This study investigated seasonal trends in bioaccumulation potential and toxic effects of mercury (Hg) in Asian clams (Corbicula fluminea) and microbial community. For this, a clam-exposure experiment was performed during summer, fall, and winter seasons in four different sites (HS1: control/clean site; HS2, HS3, and HS4: contaminated sites) of Hyeongsan River estuary, South Korea. Total mercury (THg) and methylmercury (MeHg) in whole sediments were highest at HS4 site during fall, sustained similar levels during winter, but decreased during summer. Unlike whole sediment, pore water reported higher levels in summer, and gradually declined during fall and winter. Asian clams from HS4 site collected during summer presented highest bioaccumulations of THg (521.52 μg/kg, dry weight) and MeHg (161.04 μg/kg, dry weight), which also correlated with the higher levels of Hg present in pore water in the same season. Moreover, biota-sediment-pore water accumulation factor (BSpAF) were comparatively greater in clams collected from HS2∼HS4 compared to HS1 sites, suggesting that porewater was a better indicator of accumulation of Hg. Upregulation of biomarker genes responsible for detoxifying process (gsts1), scavenging oxidative stress (cat), and protein reparation (hsp70 and hsp90) were observed in clams collected from HS2∼HS4. The overexpression of these biomarkers implied that Asian clams can be considered as promising warning tools for Hg-contamination. Both bacterial and metabolic diversities were negatively affected by higher levels of THg and MeHg. Phylum Proteobacteria was enriched in HS2∼HS4 compared to HS1. In contrast, phylum Bacteroidetes showed a reverse trend. The metabolic profile was highest in HS1 and lowest in HS4, revealing higher stress of Hg in HS4 site. Overall, the outcomes of this field study broaden the information on seasonal trends of bioaccumulation of Hg and its toxic effects. These findings may be helpful in Hg monitoring and management programs in other river systems.
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Affiliation(s)
- Dhiraj Kumar Chaudhary
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, Republic of Korea
| | - Hwansuk Kim
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, Republic of Korea
| | - Danny Reible
- Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX, USA, 79409
| | - Mikyung Lee
- Water Environmental Engineering Research Division, National Institute of Environmental Research, Hwangyong-ro 42, Seogu, Incheon, 22689, Republic of Korea
| | - Sunyoung Kim
- Water Environmental Engineering Research Division, National Institute of Environmental Research, Hwangyong-ro 42, Seogu, Incheon, 22689, Republic of Korea
| | - Lan Hee Kim
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, Republic of Korea
| | - Sungpyo Kim
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, Republic of Korea
| | - Yongseok Hong
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, Republic of Korea.
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10
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Yu RQ, Barkay T. Microbial mercury transformations: Molecules, functions and organisms. ADVANCES IN APPLIED MICROBIOLOGY 2022; 118:31-90. [PMID: 35461663 DOI: 10.1016/bs.aambs.2022.03.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Mercury (Hg) methylation, methylmercury (MeHg) demethylation, and inorganic redox transformations of Hg are microbe-mediating processes that determine the fate and cycling of Hg and MeHg in many environments, and by doing so influence the health of humans and wild life. The discovery of the Hg methylation genes, hgcAB, in the last decade together with advances in high throughput and genome sequencing methods, have resulted in an expanded appreciation of the diversity of Hg methylating microbes. This review aims to describe experimentally confirmed and recently discovered hgcAB gene-carrying Hg methylating microbes; phylogenetic and taxonomic analyses are presented. In addition, the current knowledge on transformation mechanisms, the organisms that carry them out, and the impact of environmental parameters on Hg methylation, MeHg demethylation, and inorganic Hg reduction and oxidation is summarized. This knowledge provides a foundation for future action toward mitigating the impact of environmental Hg pollution.
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Affiliation(s)
- Ri-Qing Yu
- Department of Biology, University of Texas at Tyler, Tyler, TX, United States.
| | - Tamar Barkay
- Department of Biochemistry and Microbiology, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States
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11
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Chaudhary DK, Kim KH, Lee M, Kim H, Hong Y. Insights into Bacterial Community Structure and Metabolic Diversity of Mercury-Contaminated Sediments from Hyeongsan River, Pohang, South Korea. Curr Microbiol 2022; 79:156. [PMID: 35397046 DOI: 10.1007/s00284-022-02847-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 03/16/2022] [Indexed: 11/30/2022]
Abstract
This study investigated the bacterial community structure and metabolic diversity and their relationship with Hg and other environmental variables in sediments collected from different locations (HSR-1-HSR-6) in the Hyeongsan River estuary in South Korea. The results showed that the highest total mercury (THg) and methylmercury (MeHg) concentrations were in HSR-2, with values of 4585.3 µg/kg and 13.4 µg/kg, respectively. The lowest THg (31.9 µg/kg) and MeHg (0.1 µg/kg) concentrations were found in HSR-1. Sulfate and organic matter (OM) were more influential environmental variables, revealing a positive association with THg and MeHg and negatively affecting bacterial and metabolic diversities. Bacterial and metabolic diversities were also negatively impacted by the THg and MeHg concentrations. Proteobacteria and Bacteroidetes were abundantly distributed in all the sediments. The dominance of Proteobacteria was upscaled in all the heavily Hg-contaminated sites (HSR-2-HSR-6), and it was the only phylum that showed a significant positive correlation with THg, MeHg, and OM. The genera Sulfurovum and Sulfurimonas were abundantly observed in sites with high Hg contamination, whereas Congregibacter, Gaetbulibacter, Ilumatobacter, Methylotenera, Nevskia, and Sediminibacter were only detected in low Hg-contaminated sites (HSR-1). The community-level physiological profile data showed the highest (1.0) average well color development (AWCD) value in HSR-1 and the lowest (0.45) AWCD value in HSR-2. Overall, these results demonstrated the inhibitory effects of THg, MeHg, and other environmental variables on microbial communities and metabolic diversity. These findings broaden the current knowledge on the dynamics of bacterial and metabolic diversities in Hg-contaminated sediments and might be useful in the management of Hg pollution.
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Affiliation(s)
- Dhiraj Kumar Chaudhary
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019, Republic of Korea
| | - Kyung Hee Kim
- Water Environmental Engineering Research Division, National Institute of Environmental Research, Hwangyong-ro 42, Seogu, Incheon, 22689, Republic of Korea
| | - Mikyung Lee
- Water Environmental Engineering Research Division, National Institute of Environmental Research, Hwangyong-ro 42, Seogu, Incheon, 22689, Republic of Korea
| | - Hwansuk Kim
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019, Republic of Korea
| | - Yongseok Hong
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019, Republic of Korea.
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12
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Bailon MX, Park M, Solis KL, Na Y, Chaudhary DK, Kim S, Hong Y. Reduction in mercury bioavailability to Asian clams (Corbicula fluminea) and changes in bacterial communities in sediments with activated carbon amendment. CHEMOSPHERE 2022; 291:132700. [PMID: 34710454 DOI: 10.1016/j.chemosphere.2021.132700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 08/23/2021] [Accepted: 10/24/2021] [Indexed: 06/13/2023]
Abstract
Activated carbon (AC) amendment is considered as one of the alternatives for managing and remediating mercury (Hg) contaminated sediments because of its high sorptive capacity and potential to immobilize the contaminant. For this study, the underlying mechanisms that control the reduction of Hg bioavailability in AC-amended estuarine sediments were investigated in box microcosm set-ups with 28-day Asian clam bioassay experiments. The application of diffusive gradients in thin film technique (DGT) revealed that the total mercury and methylmercury levels in sediment pore water decreased by 60%-75% in 1%-3% AC-amended sediments. This decrease subsequently led to a linear reduction in the Hg body burden in Asian clams, even at 1% sorbent mixing. These observations implied that AC amendment reduced the net flux of Hg into the pore water and overlying water, resulting in reduced Hg bioaccumulation in benthic organisms. The addition of AC to sediment also led to reduced dissolved organic carbon and several biogeochemical indicators (HS-, Mn, and Fe) in the pore water. Furthermore, the 16 S rRNA gene amplicon sequencing analysis revealed noticeable alterations in the microbial communities after AC amendment. The predominant phylum was Firmicutes in control sediment, Bacteroidetes in 1% AC-amended sediment, and Proteobacteria in both 2% and 3% AC-amended sediment samples. The genera-level analysis showed that the relative abundance of the Hg-methylators decreased as the level of AC amendment increased. These observations suggested that AC amendment decreased Hg bioavailability not only by physicochemical sorption but also by changing geochemical species and shifting the microbial community composition.
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Affiliation(s)
- Mark Xavier Bailon
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea; Department of Science and Technology, Philippine Science High School - Central Luzon Campus, Lily Hill, Clark Freeport Zone, Mabalacat City, Pampanga, 2010, Philippines
| | - Minoh Park
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea
| | - Kurt Louis Solis
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea
| | - Yeong Na
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea
| | - Dhiraj Kumar Chaudhary
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea
| | - Sungpyo Kim
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea
| | - Yongseok Hong
- Department of Environmental Engineering, Korea University Sejong Campus, 2511 Sejong-ro, Sejong City, 30019, South Korea.
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13
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Yang X, Li Z, Ma C, Yang Z, Wei J, Wang T, Wen X, Chen W, Shi X, Zhang Y, Zhang C. Microplastics influence on Hg methylation in diverse paddy soils. JOURNAL OF HAZARDOUS MATERIALS 2022; 423:126895. [PMID: 34454791 DOI: 10.1016/j.jhazmat.2021.126895] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 08/05/2021] [Accepted: 08/10/2021] [Indexed: 06/13/2023]
Abstract
Microplastics are widespread in estuarine, coastal, and deep sea sediments. The influence of microplastics on mercury (Hg) methylation in paddy soils with different characteristics, however, has not been well reported. In this research, we conducted a microcosmic experiment using red soil and alkaline soil with 2%, 7% and 10% polyvinyl chloride microplastics (PVC-MPs). Diffusive gradients in thin film (DGT) were used to test bioavailable Hg2+ and bioavailable methylmercury (MeHg) in soils. Results showed that PVC-MPs could decrease bioavailable MeHg concentrations both in red soil and alkaline soil. We demonstrated that these decreases could be due to three possible mechanisms: (1) PVC-MPs affected DOM composition, which resulted in a difference in combining capacity for bioavailable Hg2+; (2) PVC-MPs decreased MeHg via changing soil properties (including sulfate and dissolved Fe); (3) PVC-MPs affected the abundance of Proteobacteria, Firmicutes, and hgcA gene in soils. Our results emphasized the significance of investigating effects of microplastics on specific contaminants to implement effective environmental remediation strategies in polluted paddy soils.
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Affiliation(s)
- Xu Yang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Zihao Li
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Chi Ma
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Zhongzhu Yang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Jingjing Wei
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Tantan Wang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Xin Wen
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Wenhao Chen
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
| | - Xiaohong Shi
- College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot 010018, China
| | - Yi Zhang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China.
| | - Chang Zhang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China.
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14
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Lei P, Zhang J, Zhu J, Tan Q, Kwong RWM, Pan K, Jiang T, Naderi M, Zhong H. Algal Organic Matter Drives Methanogen-Mediated Methylmercury Production in Water from Eutrophic Shallow Lakes. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:10811-10820. [PMID: 34236181 DOI: 10.1021/acs.est.0c08395] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Algal blooms bring massive amounts of algal organic matter (AOM) into eutrophic lakes, which influences microbial methylmercury (MeHg) production. However, because of the complexity of AOM and its dynamic changes during algal decomposition, the relationship between AOM and microbial Hg methylators remains poorly understood, which hinders predicting MeHg production and its bioaccumulation in eutrophic shallow lakes. To address that, we explored the impacts of AOM on microbial Hg methylators and MeHg production by characterizing dissolved organic matter with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and quantifying the microbial Hg methylation gene hgcA. We first reveal that the predominance of methanogens, facilitated by eutrophication-induced carbon input, could drive MeHg production in lake water. Specifically, bioavailable components of AOM (i.e., CHONs such as aromatic proteins and soluble microbial byproduct-like materials) increased the abundances (Archaea-hgcA gene: 438-2240% higher) and activities (net CH4 production: 16.0-44.4% higher) of Archaea (e.g., methanogens). These in turn led to enhanced dissolved MeHg levels (24.3-15,918% higher) for three major eutrophic shallow lakes in China. Nevertheless, our model results indicate that AOM-facilitated MeHg production could be offset by AOM-induced MeHg biodilution under eutrophication. Our study would help reduce uncertainties in predicting MeHg production, providing a basis for mitigating the MeHg risk in eutrophic lakes.
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Affiliation(s)
- Pei Lei
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, P. R. China
| | - Jin Zhang
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, P. R. China
| | - Jinjie Zhu
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, P. R. China
| | - Qiaoguo Tan
- Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, College of the Environment and Ecology and Center for Marine Environmental Chemistry and Toxicology, Xiamen University, Xiamen, Fujian 361102, P. R. China
| | - Raymond W M Kwong
- Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada
| | - Ke Pan
- Institute for Advanced Study, Shenzhen University, Shenzhen 518060, P. R. China
| | - Tao Jiang
- Interdisciplinary Research Centre for Agriculture Green Development in Yangtze River Basin, College of Resources and Environment, Southwest University, Chongqing 400716, China
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå SE-90183, Sweden
| | - Mohammad Naderi
- Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada
| | - Huan Zhong
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, P. R. China
- Environmental and Life Science Program (EnLS), Trent University, Peterborough, Ontario K9L 0G2, Canada
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15
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Dai SS, Yang Z, Tong Y, Chen L, Liu SY, Pan R, Li Y, Zhang CJ, Liu YR, Huang Q. Global distribution and environmental drivers of methylmercury production in sediments. JOURNAL OF HAZARDOUS MATERIALS 2021; 407:124700. [PMID: 33333388 DOI: 10.1016/j.jhazmat.2020.124700] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 11/11/2020] [Accepted: 11/25/2020] [Indexed: 06/12/2023]
Abstract
Neurotoxic methylmercury (MeHg) in environments poses substantial risks to human health. Saturated sediments are basic sources of MeHg in food chains; however, distribution patterns and environmental drivers of MeHg at a global scale remain largely unexplored. Here, we characterized global patterns of MeHg distribution and environmental drivers of MeHg production based on 495 sediment samples across five typical ecosystems from the literature (1995-2018) and our own field survey. Our results showed the MeHg concentration ranged from 0.009 to 55.7 μg kg-1 across the different ecosystems, and the highest MeHg concentration and Hg methylation potential were from the sediments of paddy and marine environments, respectively. Further, using combined analysis of random forest and structural equation modeling, we identified temperature and precipitation as important regulators of MeHg production after accounting for the well-known drivers including Hg availability and sediment geochemistry. More importantly, we found increased MeHg production in sediments with elevated mean annual Hg precipitation, and warmer temperature could also accelerate MeHg production by facilitating activities of microbial methylators. Together, this work advances our understanding of global MeHg distribution in sediments and environmental drivers, which are fundamental to the prediction and management of MeHg production and its potential health risk globally.
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Affiliation(s)
- Shu-Shen Dai
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Ziming Yang
- Department of Chemistry, Oakland University, Rochester, MI 48309, United States
| | - Yindong Tong
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Long Chen
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographic Sciences, East China Normal University, Shanghai 200241, China
| | - Si-Yuan Liu
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Rong Pan
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Yanbin Li
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
| | - Cui-Jing Zhang
- Shenzhen Key Laboratory of Marine Microbiome Engineering, Institute for Advanced Study, Shenzhen University, Shenzhen 518060, China
| | - Yu-Rong Liu
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; Hubei Key Laboratory of Soil Environment and Pollution Remediation, Wuhan 430070, China.
| | - Qiaoyun Huang
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; Hubei Key Laboratory of Soil Environment and Pollution Remediation, Wuhan 430070, China
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16
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Carrell AA, Schwartz GE, Cregger MA, Gionfriddo CM, Elias DA, Wilpiszeski RL, Klingeman DM, Wymore AM, Muller KA, Brooks SC. Nutrient Exposure Alters Microbial Composition, Structure, and Mercury Methylating Activity in Periphyton in a Contaminated Watershed. Front Microbiol 2021; 12:647861. [PMID: 33815336 PMCID: PMC8017159 DOI: 10.3389/fmicb.2021.647861] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 02/22/2021] [Indexed: 01/04/2023] Open
Abstract
The conversion of mercury (Hg) to monomethylmercury (MMHg) is a critical area of concern in global Hg cycling. Periphyton biofilms may harbor significant amounts of MMHg but little is known about the Hg-methylating potential of the periphyton microbiome. Therefore, we used high-throughput amplicon sequencing of the 16S rRNA gene, ITS2 region, and Hg methylation gene pair (hgcAB) to characterize the archaea/bacteria, fungi, and Hg-methylating microorganisms in periphyton communities grown in a contaminated watershed in East Tennessee (United States). Furthermore, we examined how nutrient amendments (nitrate and/or phosphate) altered periphyton community structure and function. We found that bacterial/archaeal richness in experimental conditions decreased in summer and increased in autumn relative to control treatments, while fungal diversity generally increased in summer and decreased in autumn relative to control treatments. Interestingly, the Hg-methylating communities were dominated by Proteobacteria followed by Candidatus Atribacteria across both seasons. Surprisingly, Hg methylation potential correlated with numerous bacterial families that do not contain hgcAB, suggesting that the overall microbiome structure of periphyton communities influences rates of Hg transformation within these microbial mats. To further explore these complex community interactions, we performed a microbial network analysis and found that the nitrate-amended treatment resulted in the highest number of hub taxa that also corresponded with enhanced Hg methylation potential. This work provides insight into community interactions within the periphyton microbiome that may contribute to Hg cycling and will inform future research that will focus on establishing mixed microbial consortia to uncover mechanisms driving shifts in Hg cycling within periphyton habitats.
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Affiliation(s)
- Alyssa A Carrell
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Grace E Schwartz
- Oak Ridge National Laboratory, Environmental Science Division, Oak Ridge, TN, United States.,Department of Chemistry, Wofford College, Spartanburg, SC, United States
| | - Melissa A Cregger
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Caitlin M Gionfriddo
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States.,Smithsonian Environmental Research Center, Edgewater, MD, United States
| | - Dwayne A Elias
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Regina L Wilpiszeski
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Dawn M Klingeman
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Ann M Wymore
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Katherine A Muller
- Pacific Northwest National Laboratory, Earth Systems Science Division, Richland, WA, United States
| | - Scott C Brooks
- Oak Ridge National Laboratory, Environmental Science Division, Oak Ridge, TN, United States
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17
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Wang Y, Roth S, Schaefer JK, Reinfelder JR, Yee N. Production of methylmercury by methanogens in mercury contaminated estuarine sediments. FEMS Microbiol Lett 2020; 367:6006876. [PMID: 33242089 DOI: 10.1093/femsle/fnaa196] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 11/24/2020] [Indexed: 11/14/2022] Open
Abstract
Anaerobic bacteria are known to produce neurotoxic methylmercury [MeHg] when elemental mercury [Hg(0)] is provided as the sole mercury source. In this study, we examined the formation of MeHg in anaerobic incubations of sediment collected from the San Jacinto River estuary (Texas, USA) amended with aqueous Hg(0) to investigate the microbial communities involved in the conversion of Hg(0) to MeHg. The results show that the addition of the methanogen inhibitor 2-bromoethanesulfonate (BES) significantly decreased MeHg production. The mercury methylation gene, hgcA, was detected in these sediments using archaeal specific primers, and 16S rRNA sequencing showed that a member of the Methanosarcinaceae family of methanogens was active. These results suggest that methanogenic archaea play an underappreciated role in the production of MeHg in estuarine sediments contaminated with Hg(0).
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Affiliation(s)
- Yuwei Wang
- Department of Environmental Sciences, Rutgers University, New Brunswick, 14 College Farm Road, NJ 08901, USA
| | - Spencer Roth
- Department of Environmental Sciences, Rutgers University, New Brunswick, 14 College Farm Road, NJ 08901, USA.,Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, 76 Lipman Drive, NJ 08901, USA
| | - Jeffra K Schaefer
- Department of Environmental Sciences, Rutgers University, New Brunswick, 14 College Farm Road, NJ 08901, USA
| | - John R Reinfelder
- Department of Environmental Sciences, Rutgers University, New Brunswick, 14 College Farm Road, NJ 08901, USA
| | - Nathan Yee
- Department of Environmental Sciences, Rutgers University, New Brunswick, 14 College Farm Road, NJ 08901, USA
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18
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Wang Y, Sun Y, He T, Deng H, Wang Z, Wang J, Zheng X, Zhou L, Zhong H. Biochar amendment mitigates the health risks of dietary methylmercury exposure from rice consumption in mercury-contaminated areas. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2020; 267:115547. [PMID: 33254602 DOI: 10.1016/j.envpol.2020.115547] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 08/23/2020] [Accepted: 08/25/2020] [Indexed: 06/12/2023]
Abstract
The accumulation of methylmercury (MeHg) in rice is an important MeHg exposure pathway in humans in several mercury (Hg)-contaminated areas. In this study, the effects of low-dose biochar (BC) amendment (0.3%, w/w) on MeHg mobility/phytoavailability in different Hg-contaminated paddy soils, MeHg accumulation in rice plants and the health risks associated with MeHg-laden rice consumption were investigated. Soils amended with different doses of bamboo-derived BC (0.3, 0.5, and 1%, w/w) were incubated under anoxic conditions in microcosm experiments. In addition, pot experiments were conducted involving rice cultivation with a low BC application rate (0.3%, w/w). We observed that (1) the fraction of extractable MeHg in soils decreased with BC addition in both the microcosm and pot experiments; (2) MeHg concentrations in the rice grains (brown rice) significantly decreased by 56-88% in response to BC amendment, which may be attributed mainly to decreases in MeHg mobility/phytoavailability in the soil; and (3) the hazard quotient (HQ) values for adults and children and fetal intelligence quotient (IQ) decrements associated with MeHg-laden rice consumption were significantly alleviated under BC amendment. Taken together, our findings suggest that a low dose of BC (0.3%, w/w) could have great potential for mitigating the health risks of dietary MeHg exposure from the consumption of rice grown in mercury (Hg)-contaminated areas.
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Affiliation(s)
- Yongjie Wang
- Key Laboratory of Geographic Information Science, Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China; Institute of Eco-Chongming, East China Normal University, Shanghai, 200241, PR China
| | - Yafei Sun
- Key Laboratory of Geographic Information Science, Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Tianrong He
- Key Laboratory of Karst Environment and Geohazard Prevention, Guizhou University, Guiyang, 550003, PR China
| | - Hong Deng
- Institute of Eco-Chongming, East China Normal University, Shanghai, 200241, PR China; Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration, Technology Innovation Center for Land Spatial Eco-restoration in Metropolitan area, Ministry of Natural Resource, School of Ecological and Environmental Science, East China Normal University, Shanghai, 200241, PR China
| | - Zhigang Wang
- Key Laboratory of Geographic Information Science, Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Jiangtao Wang
- Institute of Eco-Chongming, East China Normal University, Shanghai, 200241, PR China
| | - Xiangmin Zheng
- Key Laboratory of Geographic Information Science, Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China
| | - Limin Zhou
- Key Laboratory of Geographic Information Science, Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai, 200241, PR China; Institute of Eco-Chongming, East China Normal University, Shanghai, 200241, PR China
| | - Huan Zhong
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, PR China; Environmental and Life Sciences Program (EnLS), Trent University, Peterborough, Ontario, Canada.
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19
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Zheng S, Wang B, Xu G, Liu F. Effects of Organic Phosphorus on Methylotrophic Methanogenesis in Coastal Lagoon Sediments With Seagrass ( Zostera marina) Colonization. Front Microbiol 2020; 11:1770. [PMID: 32849394 PMCID: PMC7411354 DOI: 10.3389/fmicb.2020.01770] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 07/06/2020] [Indexed: 02/03/2023] Open
Abstract
Methanogens are the major contributors of greenhouse gas methane and play significant roles in the degradation and transformation of organic matter. These organisms are particularly abundant in Swan Lake, which is a shallow lagoon located in Rongcheng Bay, Yellow Sea, northern China, where eutrophication from overfertilization commonly results in anoxic environments. High organic phosphorus content is a key component of the total phosphorus in Swan Lake and is possibly a key factor affecting the eutrophication and carbon and nitrogen cycling in Swan Lake. The effects of organic phosphorus on eutrophication have been well-studied with respect to bacteria, such as cyanobacteria, unlike the effects of organic phosphorus on methanogenesis. In this study, different sediment layer samples of seagrass-vegetated and unvegetated areas in Swan Lake were investigated to understand the effects of organic phosphorus on methylotrophic methanogenesis. The results showed that phytate phosphorus significantly promoted methane production in the deepest sediment layer of vegetated regions but suppressed it in unvegetated regions. Amplicon sequencing revealed that methylotrophic Methanococcoides actively dominated in all enrichment samples from both regions with additions of trimethylamine or phytate phosphorus, whereas methylotrophic Methanolobus and Methanosarcina predominated in the enrichments obtained from vegetated and unvegetated sediments, respectively. These results prompted further study of the effects of phytate phosphorus on two methanogen isolates, Methanolobus psychrophilus, a type strain, Methanosarcina mazei, an isolate from Swan Lake sediments. Cultivation experiments showed that phytate phosphorus could inhibit methane production by M. psychrophilus but promote methane production by M. mazei. These culture-based studies revealed the effects of organic phosphorus on methylotrophic methanogenesis in coastal lagoon sediments and improves our understanding of the mechanisms of organic carbon cycling leading to methanogenesis mediated by organic phosphorus dynamics in coastal wetlands.
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Affiliation(s)
- Shiling Zheng
- Key Laboratory of Coastal Biology and Biological Resources Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China.,Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology, Qingdao, China.,Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China
| | - Bingchen Wang
- Key Laboratory of Coastal Biology and Biological Resources Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China.,College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao, China
| | - Gang Xu
- Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China
| | - Fanghua Liu
- Key Laboratory of Coastal Biology and Biological Resources Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China.,Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology, Qingdao, China.,Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Institute of Eco-environmental Science and Technology, Guangdong Academy of Sciences, Guangzhou, China
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20
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Schaefer JK, Kronberg R, Björn E, Skyllberg U. Anaerobic guilds responsible for mercury methylation in boreal wetlands of varied trophic status serving as either a methylmercury source or sink. Environ Microbiol 2020; 22:3685-3699. [DOI: 10.1111/1462-2920.15134] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 06/16/2020] [Indexed: 11/30/2022]
Affiliation(s)
- Jeffra K Schaefer
- Department of Environmental Sciences Rutgers University 14 College Farm Road, New Brunswick NJ 08901 USA
| | - Rose‐Marie Kronberg
- Department of Forest Ecology and Management Swedish University of Agricultural Sciences Umeå SE‐901 83 Sweden
| | - Erik Björn
- Department of Chemistry Umeå University Umeå SE‐901 87 Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management Swedish University of Agricultural Sciences Umeå SE‐901 83 Sweden
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21
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Bravo AG, Cosio C. Biotic formation of methylmercury: A bio-physico-chemical conundrum. LIMNOLOGY AND OCEANOGRAPHY 2020; 65:1010-1027. [PMID: 32612306 PMCID: PMC7319479 DOI: 10.1002/lno.11366] [Citation(s) in RCA: 62] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 09/17/2019] [Accepted: 10/02/2019] [Indexed: 05/11/2023]
Abstract
Mercury (Hg) is a natural and widespread trace metal, but is considered a priority pollutant, particularly its organic form methylmercury (MMHg), because of human's exposure to MMHg through fish consumption. Pioneering studies showed the methylation of divalent Hg (HgII) to MMHg to occur under oxygen-limited conditions and to depend on the activity of anaerobic microorganisms. Recent studies identified the hgcAB gene cluster in microorganisms with the capacity to methylate HgII and unveiled a much wider range of species and environmental conditions producing MMHg than previously expected. Here, we review the recent knowledge and approaches used to understand HgII-methylation, microbial biodiversity and activity involved in these processes, and we highlight the current limits for predicting MMHg concentrations in the environment. The available data unveil the fact that HgII methylation is a bio-physico-chemical conundrum in which the efficiency of biological HgII methylation appears to depend chiefly on HgII and nutrients availability, the abundance of electron acceptors such as sulfate or iron, the abundance and composition of organic matter as well as the activity and structure of the microbial community. An increased knowledge of the relationship between microbial community composition, physico-chemical conditions, MMHg production, and demethylation is necessary to predict variability in MMHg concentrations across environments.
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Affiliation(s)
- Andrea G. Bravo
- Department of Marine Biology and Oceanography, Institute of Marine SciencesSpanish National Research Council (CSIC)BarcelonaSpain
| | - Claudia Cosio
- Université de Reims Champagne Ardennes, UMR‐I 02 INERIS‐URCA‐ULH SEBIO, Unité Stress Environnementaux et BIOsurveillance des milieux aquatiquesReimsFrance
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22
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Wang AO, Ptacek CJ, Blowes DW, Finfrock YZ, Paktunc D, Mack EE. Use of hardwood and sulfurized-hardwood biochars as amendments to floodplain soil from South River, VA, USA: Impacts of drying-rewetting on Hg removal. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 712:136018. [PMID: 32050399 DOI: 10.1016/j.scitotenv.2019.136018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 11/24/2019] [Accepted: 12/07/2019] [Indexed: 06/10/2023]
Abstract
Periodic flooding and drying conditions in floodplains affect the mobility and bioavailability of Hg in aquatic sediments and surrounding soils. Sulfurized materials have been recently proposed as Hg sorbents due to their high affinity to bind Hg, while sulfurizing organic matter may enhance methylmercury (MeHg) production, offsetting the beneficial aspects of these materials. This study evaluated hardwood biochar (OAK) and sulfurized-hardwood biochar (MOAK) as soil amendments for controlling Hg release in a contaminated floodplain soil under conditions representative of periodic flooding and drying in microcosm experiments in three stages: (1) wet biochar amended-systems with river water in an anoxic environment up to 200 d; (2) dry selected reaction vessels in an oxic environment for 90 d; (3) rewet such vessels with river water in an anoxic environment for 90 d. In Stage 1, greater Hg removal (17-98% for unfiltered total Hg (THg) and 47-99% for 0.45-μm THg) and lower MeHg concentrations (<20 ng L-1) were observed in MOAK-amended systems (10%MOAKs). In Stage 3, release of Hg in 10%MOAKs was eight-fold lower than in soil controls (SedCTRs), while increases in aqueous (up to 21 ng L-1) and solid (up to 88 ng g-1) MeHg concentrations were observed. The increases in MeHg corresponded to elevated aqueous concentrations of Mn, Fe, SO42-, and HS- in Stage 3. Results of S K-edge X-ray absorption near edge structure (XANES) analysis suggest oxidation of S in Stage 2 and formation of polysulfur in Stage 3. Results of pyrosequencing analysis indicate sulfate-reducing bacteria (SRB) became abundant in Stage 3 in 10%MOAKs. The shifts in biogeochemical conditions in 10%MOAKs in Stage 3 may increase the bioavailability of Hg to methylating bacteria. The results suggest limited impacts on Hg removal during drying and rewetting, while changes in biogeochemical conditions may affect MeHg production in sulfurized biochar-amended systems.
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Affiliation(s)
- Alana O Wang
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W, Waterloo, ON N2L 3G1, Canada
| | - Carol J Ptacek
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W, Waterloo, ON N2L 3G1, Canada.
| | - David W Blowes
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W, Waterloo, ON N2L 3G1, Canada
| | - Y Zou Finfrock
- CLS@APS, Sector 20, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA; Science Division, Canadian Light Source Inc., Saskatoon, SK S7N 2V3, Canada
| | - Dogan Paktunc
- CanmetMINING, Natural Resource Canada, Ottawa, ON K1A 0G1, Canada
| | - E Erin Mack
- Formerly E. I. du Pont de Nemours and Company, 974 Centre Road, Wilmington, DE 19805, USA
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23
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Mercury-methylating bacteria are associated with copepods: A proof-of-principle survey in the Baltic Sea. PLoS One 2020; 15:e0230310. [PMID: 32176728 PMCID: PMC7075563 DOI: 10.1371/journal.pone.0230310] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Accepted: 02/26/2020] [Indexed: 01/08/2023] Open
Abstract
Methylmercury (MeHg) is a potent neurotoxin that biomagnifies in marine food webs. Inorganic mercury (Hg) methylation is conducted by heterotrophic bacteria inhabiting sediment or settling detritus, but endogenous methylation by the gut microbiome of animals in the lower food webs is another possible source. We examined the occurrence of the bacterial gene (hgcA), required for Hg methylation, in the guts of dominant zooplankters in the Northern Baltic Sea. A qPCR assay targeting the hgcA sequence in three main clades (Deltaproteobacteria, Firmicutes and Archaea) was used in the field-collected specimens of copepods (Acartia bifilosa, Eurytemora affinis, Pseudocalanus acuspes and Limnocalanus macrurus) and cladocerans (Bosmina coregoni maritima and Cercopagis pengoi). All copepods were found to carry hgcA genes in their gut microbiome, whereas no amplification was recorded in the cladocerans. In the copepods, hgcA genes belonging to only Deltaproteobacteria and Firmicutes were detected. These findings suggest a possibility that endogenous Hg methylation occurs in zooplankton and may contribute to seasonal, spatial and vertical MeHg variability in the water column and food webs. Additional molecular and metagenomics studies are needed to identify bacteria carrying hgcA genes and improve their quantification in microbiota.
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24
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Lavoie NC, Grégoire DS, Stenzler BR, Poulain AJ. Reduced sulphur sources favour Hg II reduction during anoxygenic photosynthesis by Heliobacteria. GEOBIOLOGY 2020; 18:70-79. [PMID: 31536173 DOI: 10.1111/gbi.12364] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Revised: 08/16/2019] [Accepted: 08/31/2019] [Indexed: 06/10/2023]
Abstract
The consumption of rice has become a global food safety issue because rice paddies support the production of high levels of the potent neurotoxin, methylmercury. The production of methylmercury is carried out by chemotrophic anaerobes that rely on a diversity of terminal electron acceptors, namely sulphate. Sulphur can be a limiting nutrient in rice paddies, and sulphate amendments are often used to stimulate crop production, which can increase methylmercury production. Mercury (Hg) redox cycling can affect Hg methylation by controlling the delivery of inorganic Hg substrates to methylators in anoxic habitats. Whereas sulphur is recognized as a key substrate controlling methylmercury production, the controls sulphur exerts on other microbe-mediated Hg transformations remain poorly understood. To explore the potential coupling between sulphur assimilation and anaerobic HgII reduction to Hg0 , we studied Heliobacillus mobilis, a mesophilic anoxygenic phototroph representative from the Heliobacteriacea family originally isolated from a rice paddy. Here, we tested whether the redox state of the sulphur sources available to H. mobilis would affect its ability to reduce HgII . By comparing Hg0 production over a redox gradient of sulphur sources, we demonstrate that phototrophic HgII reduction is favoured in the presence of reduced sulphur sources such as thiosulphate and cysteine. We also show that cysteine exerts dynamic control on Hg cycling by affecting not only Hg's bioavailability but also its abiotic photoreduction under low light conditions. Specifically, in the absence of cells we show that organic matter (as yeast extract) and cysteine are both required for photoreduction to occur. This study offers insights into how one of the most primitive forms of photosynthesis affects Hg redox transformations and frames Heliobacteria as key players in Hg cycling within paddy soils, forming a basis for management strategies to mitigate Hg accumulation in rice.
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Affiliation(s)
- Noémie C Lavoie
- Department of Biology, Faculty of Sciences, University of Ottawa, Ottawa, Ontario, Canada
| | - Daniel S Grégoire
- Department of Biology, Faculty of Sciences, University of Ottawa, Ottawa, Ontario, Canada
| | - Bejamin R Stenzler
- Department of Biology, Faculty of Sciences, University of Ottawa, Ottawa, Ontario, Canada
| | - Alexandre J Poulain
- Department of Biology, Faculty of Sciences, University of Ottawa, Ottawa, Ontario, Canada
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25
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Schwartz GE, Olsen TA, Muller KA, Brooks SC. Ecosystem Controls on Methylmercury Production by Periphyton Biofilms in a Contaminated Stream: Implications for Predictive Modeling. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2019; 38:2426-2435. [PMID: 31365146 DOI: 10.1002/etc.4551] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 06/12/2019] [Accepted: 07/29/2019] [Indexed: 06/10/2023]
Abstract
Periphyton biofilms produce a substantial fraction of the overall monomethylmercury (MMHg) flux in East Fork Poplar Creek, an industrially contaminated, freshwater creek in Oak Ridge, Tennessee. We examined periphyton MMHg production across seasons, locations, and light conditions using mercury stable isotopes. Methylation and demethylation rate potentials (km, trans av and kd, trans av , respectively) were calculated using a transient availability kinetic model. Light exposure and season were significant predictors of km, trans av , with greater values in full light exposure and in the summer. Season, light exposure, and location were significant predictors of kd, trans av , which was highest in dark conditions, in the spring, and at the upstream location. Light exposure was the controlling factor for net MMHg production, with positive production for periphyton grown under full light exposure and net demethylation for periphyton grown in the dark. Ambient MMHg and km, trans av were significantly correlated. Transient availability rate potentials were 15 times higher for km and 9 times higher for kd compared to full availability rate potentials (km, full av and kd, full av ) calculated at 1 d. No significant model for the prediction of km, full av or kd, full av could be constructed using light, season, and location. In addition, there were no significant differences among treatments for the full availability km, full av , kd, full av , or net MMHg calculated using the full availability rate potentials. km, full av was not correlated with ambient MMHg concentrations. The present results underscore the importance of applying transient availability kinetics to MMHg production data when estimating MMHg production potential and flux. Environ Toxicol Chem 2019;38:2426-2435. © 2019 SETAC.
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Affiliation(s)
- Grace E Schwartz
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Todd A Olsen
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Katherine A Muller
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Scott C Brooks
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
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26
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Abstract
The human gut microbiome is considered critical for establishing and maintaining intestinal function and homeostasis throughout life. Evidence for bidirectional communication with the immune and nervous systems has spawned interest in the microbiome as a key factor for human and animal health. Consequently, appreciation of the microbiome as a target of xenobiotics, including environmental pollutants such as heavy metals, has risen steadily because disruption of a healthy microbiome (dysbiosis) has been linked to unfavorable health outcomes. Thus, toxicology must consider toxicant effects on the host's microbiome as an integral part of the holobiont. We discuss current findings on the impact of toxic metals on the composition, diversity, and function of the gut microbiome as well as the modulation of metal toxicity by the microbiome. Present limitations and future needs in elucidating microbiome-metal interactions and the potential of harnessing beneficial traits of the microbiota to counteract metal toxicity are also considered.
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Affiliation(s)
- Senait Assefa
- Department of Biochemistry & Microbiology, Oklahoma State University Center for Health Sciences, Tulsa, Oklahoma, U.S.A
| | - Gerwald Köhler
- Department of Biochemistry & Microbiology, Oklahoma State University Center for Health Sciences, Tulsa, Oklahoma, U.S.A
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27
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Christensen GA, Gionfriddo CM, King AJ, Moberly JG, Miller CL, Somenahally AC, Callister SJ, Brewer H, Podar M, Brown SD, Palumbo AV, Brandt CC, Wymore AM, Brooks SC, Hwang C, Fields MW, Wall JD, Gilmour CC, Elias DA. Determining the Reliability of Measuring Mercury Cycling Gene Abundance with Correlations with Mercury and Methylmercury Concentrations. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:8649-8663. [PMID: 31260289 DOI: 10.1021/acs.est.8b06389] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Methylmercury (MeHg) is a bioaccumulative toxic contaminant in many ecosystems, but factors governing its production are poorly understood. Recent work has shown that the anaerobic microbial conversion of mercury (Hg) to MeHg requires the Hg-methylation genes hgcAB and that these genes can be used as biomarkers in PCR-based estimators of Hg-methylator abundance. In an effort to determine reliable methods for assessing hgcA abundance and diversity and linking them to MeHg concentrations, multiple approaches were compared including metagenomic shotgun sequencing, 16S rRNA gene pyrosequencing and cloning/sequencing hgcAB gene products. Hg-methylator abundance was also determined by quantitative hgcA qPCR amplification and metaproteomics for comparison to the above measurements. Samples from eight sites were examined covering a range of total Hg (HgT; 0.03-14 mg kg-1 dry wt. soil) and MeHg (0.05-27 μg kg-1 dry wt. soil) concentrations. In the metagenome and amplicon sequencing of hgcAB diversity, the Deltaproteobacteria were the dominant Hg-methylators while Firmicutes and methanogenic Archaea were typically ∼50% less abundant. This was consistent with metaproteomics estimates where the Deltaproteobacteria were steadily higher. The 16S rRNA gene pyrosequencing did not have sufficient resolution to identify hgcAB+ species. Metagenomic and hgcAB results were similar for Hg-methylator diversity and clade-specific qPCR-based approaches for hgcA are only appropriate when comparing the abundance of a particular clade across various samples. Weak correlations between Hg-methylating bacteria and soil Hg concentrations were observed for similar environmental samples, but overall total Hg and MeHg concentrations poorly correlated with Hg-cycling genes.
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Affiliation(s)
- Geoff A Christensen
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Caitlin M Gionfriddo
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Andrew J King
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - James G Moberly
- College of Engineering , University of Idaho , Moscow , Idaho 83844 , United States
| | - Carrie L Miller
- School of Theoretical and Applied Science , Ramapo College of New Jersey , Mahwah , New Jersey 07430 , United States
| | - Anil C Somenahally
- Department of Soil and Crop Sciences , Texas A&M University , Overton , Texas 77843-2474 , United States
| | - Stephen J Callister
- Biological Sciences Division , Pacific Northwest National Laboratory , Richland , Washington 99352 , United States
| | - Heather Brewer
- Biological Sciences Division , Pacific Northwest National Laboratory , Richland , Washington 99352 , United States
| | - Mircea Podar
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Steven D Brown
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Anthony V Palumbo
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Craig C Brandt
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Ann M Wymore
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
| | - Scott C Brooks
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37830 , United States
| | - Chiachi Hwang
- Center for Biofilm Engineering , Montana State University , Bozeman , Montana 59717 , United States
| | - Matthew W Fields
- Department of Microbiology and Immunology , Montana State University , Bozeman , Montana 59717 , United States
- Center for Biofilm Engineering , Montana State University , Bozeman , Montana 59717 , United States
| | - Judy D Wall
- Department of Biochemistry , University of Missouri , Columbia , Missouri 65211 , United States
| | - Cynthia C Gilmour
- Smithsonian Environmental Research Center , Edgewater , Maryland 21037 , United States
| | - Dwayne A Elias
- Biosciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831-6342 , United States
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28
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Beckers F, Awad YM, Beiyuan J, Abrigata J, Mothes S, Tsang DCW, Ok YS, Rinklebe J. Impact of biochar on mobilization, methylation, and ethylation of mercury under dynamic redox conditions in a contaminated floodplain soil. ENVIRONMENT INTERNATIONAL 2019; 127:276-290. [PMID: 30951944 DOI: 10.1016/j.envint.2019.03.040] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 03/14/2019] [Accepted: 03/14/2019] [Indexed: 06/09/2023]
Abstract
Mercury (Hg) is a highly toxic element, which is frequently enriched in flooded soils due to its anthropogenic release. The mobilization of Hg and its species is of ultimate importance since it controls the transfer into the groundwater and plants and finally ends in the food chain, which has large implications on human health. Therefore, the remediation of those contaminated sites is an urgent need to protect humans and the environment. Often, the stabilization of Hg using amendments is a reliable option and biochar is considered a candidate to fulfill this purpose. We tested two different pine cone biochars pyrolyzed at 200 °C or 500 °C, respectively, with a view to decrease the mobilization of total Hg (Hgt), methylmercury (MeHg), and ethylmercury (EtHg) and/or the formation of MeHg and EtHg in a contaminated floodplain soil (Hgt: 41 mg/kg). We used a highly sophisticated automated biogeochemical microcosm setup to systematically alter the redox conditions from ~-150 to 300 mV. We continuously monitored the redox potential (EH) along with pH and determined dissolved organic carbon (DOC), SUVA254, chloride (Cl-), sulfate (SO42-), iron (Fe), and manganese (Mn) to be able to explain the mobilization of Hg and its species. However, the impact of biochar addition on Hg mobilization was limited. We did not observe a significant decrease of Hgt, MeHg, and EtHg concentrations after treating the soil with the different biochars, presumably because potential binding sites for Hg were occupied by other ions and/or blocked by biofilm. Solubilization of Hg bound to DOC upon flooding of the soils might have occurred which could be an indirect impact of EH on Hg mobilization. Nevertheless, Hgt, MeHg, and EtHg in the slurry fluctuated between 0.9 and 52.0 μg/l, 11.1 to 406.0 ng/l, and 2.3 to 20.8 ng/l, respectively, under dynamic redox conditions. Total Hg concentrations were inversely related to the EH; however, ethylation of Hg was favored at an EH around 0 mV while methylation was enhanced between -50 and 100 mV. Phospholipid fatty acid profiles suggest that sulfate-reducing bacteria may have been the principal methylators in our experiment. In future, various biochars should be tested to evaluate their potential in decreasing the mobilization of Hg and to impede the formation of MeHg and EtHg under dynamic redox conditions in frequently flooded soils.
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Affiliation(s)
- Felix Beckers
- University of Wuppertal, Institute of Foundation Engineering, Waste and Water Management, School of Architecture and Civil Engineering, Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany
| | - Yasser Mahmoud Awad
- University of Wuppertal, Institute of Foundation Engineering, Waste and Water Management, School of Architecture and Civil Engineering, Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany; Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI) & Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Republic of Korea; Faculty of Agriculture, Suez Canal University, Ismailia 41522, Egypt
| | - Jingzi Beiyuan
- University of Wuppertal, Institute of Foundation Engineering, Waste and Water Management, School of Architecture and Civil Engineering, Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany; School of Environment and Chemical Engineering, Foshan University, Foshan, Guangdong, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
| | - Jens Abrigata
- University of Wuppertal, Institute of Foundation Engineering, Waste and Water Management, School of Architecture and Civil Engineering, Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany
| | - Sibylle Mothes
- UFZ Helmholtz Centre for Environmental Research, Department of Analytical Chemistry, Permoserstraße 15, 04318 Leipzig, Germany
| | - Daniel C W Tsang
- Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
| | - Yong Sik Ok
- Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI) & Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Republic of Korea.
| | - Jörg Rinklebe
- University of Wuppertal, Institute of Foundation Engineering, Waste and Water Management, School of Architecture and Civil Engineering, Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany; Department of Environment, Energy & Geoinformatics, Sejong University, 98 Gunja-Dong, Guangjin-Gu, Seoul, Republic of Korea.
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29
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Mangal V, Stenzler BR, Poulain AJ, Guéguen C. Aerobic and Anaerobic Bacterial Mercury Uptake is Driven by Algal Organic Matter Composition and Molecular Weight. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:157-165. [PMID: 30516365 DOI: 10.1021/acs.est.8b04909] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The biological mobilization of mercury (Hg) into microbes capable of Hg methylation is one of the limiting steps in the formation of the neurotoxin methylmercury (MeHg). Although algal dissolved organic matter (DOM) has been associated with increased MeHg production, the relationship between bacterial Hg uptake and algal DOM remains unexplored. In this study, we aimed to address how the quantity and quality of DOM, freshly harvested from several algae, affected the bacterial uptake of Hg with the use of a biosensor capable of functioning both aerobically and anaerobically. We combined biosensor measurements with high-resolution mass spectrometry and field-flow fractionation to elucidate how DOM composition and molecular weight influenced microbial Hg uptake. We showed that freshly harvested DOM from Chlorophyte and Euglena mutabilis strongly inhibited aerobic and anaerobic Hg uptake, whereas DOM harvested from Euglena gracilis did not exhibit this same pronounced effect. Once fractionated, we found that amino acids and polyamines, most abundant in Euglena gracilis DOM, were positively correlated to increase Hg uptake, suggesting that these molecules are potentially underappreciated ligands affecting Hg bioavailability. As water quality is affected by eutrophication, algal community assemblages will change, leading to variations in the nature of autochthonous DOM released in aquatic systems. Our results highlight that variations in the emergent properties of DOM originating from varying algal species can have a profound effect on bacterial Hg uptake and thus methylation.
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Affiliation(s)
- Vaughn Mangal
- Environmental and Life Sciences Graduate program , Trent University , 1600 West Bank Drive Peterborough ON Canada , K9J 7B8
| | - Benjamin R Stenzler
- Biology Department , University of Ottawa , 30 Marie Curie , Ottawa ON Canada , K1N 6N5
| | - Alexandre J Poulain
- Biology Department , University of Ottawa , 30 Marie Curie , Ottawa ON Canada , K1N 6N5
| | - Celine Guéguen
- Chemistry Department , Trent University , 1600 West Bank Drive Peterborough ON Canada , K9J 7B8
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30
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Liu YR, Johs A, Bi L, Lu X, Hu HW, Sun D, He JZ, Gu B. Unraveling Microbial Communities Associated with Methylmercury Production in Paddy Soils. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:13110-13118. [PMID: 30335986 DOI: 10.1021/acs.est.8b03052] [Citation(s) in RCA: 96] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Rice consumption is now recognized as an important pathway of human exposure to the neurotoxin methylmercury (MeHg), particularly in countries where rice is a staple food. Although the discovery of a two-gene cluster hgcAB has linked Hg methylation to several phylogenetically diverse groups of anaerobic microorganisms converting inorganic mercury (Hg) to MeHg, the prevalence and diversity of Hg methylators in microbial communities of rice paddy soils remain unclear. We characterized the abundance and distribution of hgcAB genes using third-generation PacBio long-read sequencing and Illumina short-read metagenomic sequencing, in combination with quantitative PCR analyses in several mine-impacted paddy soils from southwest China. Both Illumina and PacBio sequencing analyses revealed that Hg methylating communities were dominated by iron-reducing bacteria (i.e., Geobacter) and methanogens, with a relatively low abundance of hgcA + sulfate-reducing bacteria in the soil. A positive correlation was observed between the MeHg content in soil and the relative abundance of Geobacter carrying the hgcA gene. Phylogenetic analysis also uncovered some hgcAB sequences closely related to three novel Hg methylators, Geobacter anodireducens, Desulfuromonas sp. DDH964, and Desulfovibrio sp. J2, among which G. anodireducens was validated for its ability to methylate Hg. These findings shed new light on microbial community composition and major clades likely driving Hg methylation in rice paddy soils.
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Affiliation(s)
- Yu-Rong Liu
- State Key Laboratory of Urban and Regional Ecology , Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing Shi 100085 , China
| | - Alexander Johs
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Li Bi
- State Key Laboratory of Urban and Regional Ecology , Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing Shi 100085 , China
| | - Xia Lu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Hang-Wei Hu
- Department of Veterinary and Agricultural Sciences , The University of Melbourne , Melbourne , Victoria 3004 , Australia
| | - Dan Sun
- Ocean College , Zhejiang University , Zhejiang , 310058 , China
| | - Ji-Zheng He
- State Key Laboratory of Urban and Regional Ecology , Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing Shi 100085 , China
- Department of Veterinary and Agricultural Sciences , The University of Melbourne , Melbourne , Victoria 3004 , Australia
| | - Baohua Gu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- Department of Biosystems Engineering and Soil Science , University of Tennessee , Knoxville , Tennessee 37996 , United States
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Methanogens and Iron-Reducing Bacteria: the Overlooked Members of Mercury-Methylating Microbial Communities in Boreal Lakes. Appl Environ Microbiol 2018; 84:AEM.01774-18. [PMID: 30242005 PMCID: PMC6238055 DOI: 10.1128/aem.01774-18] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2018] [Accepted: 09/15/2018] [Indexed: 12/28/2022] Open
Abstract
Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment. Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the hgcA gene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA and hgcA genes. Our results show that in the lake sediments, Methanomicrobiales and Geobacteraceae also represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes. IMPORTANCE Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.
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Abstract
Mercury (Hg) is a global pollutant emitted primarily as gaseous Hg0 that is deposited in aquatic and terrestrial ecosystems following its oxidation to HgII. From that point, microbes play a key role in determining Hg’s fate in the environment by participating in sequestration, oxidation, reduction, and methylation reactions. A wide diversity of chemotrophic and phototrophic microbes occupying oxic and anoxic habitats are known to participate directly in Hg cycling. Over the last few years, new findings have come to light that have greatly improved our mechanistic understanding of microbe-mediated Hg cycling pathways in the environment. In this review, we summarize recent advances in microbially mediated Hg cycling and take the opportunity to compare the relatively well-studied chemotrophic pathways to poorly understood phototrophic pathways. We present how the use of genomic and analytical tools can be used to understand Hg transformations and the physiological context of recently discovered cometabolic Hg transformations supported in anaerobes and phototrophs. Finally, we propose a conceptual framework that emphasizes the role that phototrophs play in environmental Hg redox cycling and the importance of better characterizing such pathways in the face of the environmental changes currently underway.
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Affiliation(s)
- Daniel S. Grégoire
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - Alexandre J. Poulain
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
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Ndu U, Christensen GA, Rivera NA, Gionfriddo CM, Deshusses MA, Elias DA, Hsu-Kim H. Quantification of Mercury Bioavailability for Methylation Using Diffusive Gradient in Thin-Film Samplers. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:8521-8529. [PMID: 29920204 PMCID: PMC6085726 DOI: 10.1021/acs.est.8b00647] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 05/03/2018] [Accepted: 06/19/2018] [Indexed: 05/25/2023]
Abstract
Mercury-contaminated sediment and water contain various Hg species, with a small fraction available for microbial conversion to the bioaccumulative neurotoxin monomethylmercury (MeHg). Quantification of this available Hg pool is needed to prioritize sites for risk management. This study compared the efficacy of diffusive gradient in thin-film (DGT) passive samplers to a thiol-based selective extraction method with glutathione (GSH) and conventional filtration (<0.2 μm) as indicators of Hg bioavailability. Anaerobic sediment slurry microcosms were amended with isotopically labeled inorganic Hg "endmembers" (dissolved Hg2+, Hg-humic acid, Hg-sorbed to FeS, HgS nanoparticles) with a known range of bioavailability and methylation potentials. Net MeHg production (expressed as percent of total Hg as MeHg) over 1 week correlated with mass accumulation of Hg endmembers on the DGTs and only sometimes correlated with the 0.2 μm filter passing Hg fraction and the GSH-extractable Hg fraction. These results suggest for the first time that inorganic Hg uptake in DGTs may indicate bioavailability for methylating microbes. Moreover, the methylating microbial community assessed by hgcA gene abundance was not always consistent with methylation rates between the experiments, indicating that knowledge of the methylating community should target the transcript or protein level. Altogether, these results suggest that DGTs could be used to quantify the bioavailable Hg fraction as part of a method to assess net MeHg production potential in the environment.
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Affiliation(s)
- Udonna Ndu
- Department
of Civil and Environmental Engineering, Duke University, Box 90287, Durham, North Carolina 27708, United States
| | - Geoff A. Christensen
- Biosciences
Division, Oak Ridge National Laboratory, P.O. Box 2008, MS-6036, Oak Ridge, Tennessee 37831-6036, United States
| | - Nelson A. Rivera
- Department
of Civil and Environmental Engineering, Duke University, Box 90287, Durham, North Carolina 27708, United States
| | - Caitlin M. Gionfriddo
- Biosciences
Division, Oak Ridge National Laboratory, P.O. Box 2008, MS-6036, Oak Ridge, Tennessee 37831-6036, United States
| | - Marc A. Deshusses
- Department
of Civil and Environmental Engineering, Duke University, Box 90287, Durham, North Carolina 27708, United States
| | - Dwayne A. Elias
- Biosciences
Division, Oak Ridge National Laboratory, P.O. Box 2008, MS-6036, Oak Ridge, Tennessee 37831-6036, United States
| | - Heileen Hsu-Kim
- Department
of Civil and Environmental Engineering, Duke University, Box 90287, Durham, North Carolina 27708, United States
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Gilmour CC, Bullock AL, McBurney A, Podar M, Elias DA. Robust Mercury Methylation across Diverse Methanogenic Archaea. mBio 2018; 9:e02403-17. [PMID: 29636434 PMCID: PMC5893877 DOI: 10.1128/mbio.02403-17] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 03/13/2018] [Indexed: 11/30/2022] Open
Abstract
Methylmercury (MeHg) production was compared among nine cultured methanogenic archaea that contain hgcAB, a gene pair that codes for mercury (Hg) methylation. The methanogens tested produced MeHg at inherently different rates, even when normalized to growth rate and Hg availability. Eight of the nine tested were capable of MeHg production greater than that of spent- and uninoculated-medium controls during batch culture growth. Methanococcoides methylutens, an hgcAB+ strain with a fused gene pair, was unable to produce more MeHg than controls. Maximal conversion of Hg to MeHg through a full batch culture growth cycle for each species (except M. methylutens) ranged from 2 to >50% of the added Hg(II) or between 0.2 and 17 pmol of MeHg/mg of protein. Three of the species produced >10% MeHg. The ability to produce MeHg was confirmed in several hgcAB+ methanogens that had not previously been tested (Methanocella paludicola SANAE, Methanocorpusculum bavaricum, Methanofollis liminatans GKZPZ, and Methanosphaerula palustris E1-9c). Maximal methylation was observed at low sulfide concentrations (<100 μM) and in the presence of 0.5 to 5 mM cysteine. For M. hollandica, the addition of up to 5 mM cysteine enhanced MeHg production and cell growth in a concentration-dependent manner. As observed for bacterial Hg methylators, sulfide inhibited MeHg production. An initial evaluation of sulfide and thiol impacts on bioavailability showed methanogens responding to Hg complexation in the same way as do Deltaproteobacteria The mercury methylation rates of several methanogens rival those of the better-studied Hg-methylating sulfate- and iron-reducing DeltaproteobacteriaIMPORTANCEArchaea, specifically methanogenic organisms, play a role in mercury methylation in nature, but their global importance to MeHg production and the subsequent risk to ecosystems are not known. Methanogenesis has been linked to Hg methylation in several natural habitats where methylmercury production incurs risk to people and ecosystems, including rice paddies and permafrost. In this study, we confirm that most methanogens carrying the hgcAB gene pair are capable of Hg methylation. We found that methylation rates vary inherently among hgcAB+ methanogens but that several species are capable of MeHg production at rates that rival those of the better-know Hg-methylating sulfate- and iron-reducing bacteria. Methanogens may need to be considered equally with sulfate and iron reducers in evaluations of MeHg production in nature.
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Affiliation(s)
| | | | - Alyssa McBurney
- Smithsonian Environmental Research Center, Edgewater, Maryland, USA
| | - Mircea Podar
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Dwayne A Elias
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
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