401
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Wang P, Yao Y, Wang C, Hou J, Qian J, Miao L. Impact of macrozoobenthic bioturbation and wind fluctuation interactions on net methylmercury in freshwater lakes. WATER RESEARCH 2017; 124:320-330. [PMID: 28780357 DOI: 10.1016/j.watres.2017.07.072] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Revised: 07/05/2017] [Accepted: 07/29/2017] [Indexed: 06/07/2023]
Abstract
The methylmercury (MeHg) as the toxic fractions has presented significant threats to biota in freshwater ecosystems. Hg methylation process is demonstrated to be manipulated by biota process (benthic disturbance and algae bloom existence) as well as the abiotic influence (wind fluctuation and illumination intensity) in freshwater ecosystems. However, the mechanisms influencing Hg methylation are still unclear, and the coupled influences of the biotic and abiotic process with the shifts in variation on methylmercury remain unexplored. Accordingly, an annular flume experiment which simulated the freshwater ecosystem, was conducted for 108 days to examine the influences of typical disturbance by chironomid larvae and wind fluctuations on MeHg variation in sediment profiles. The in-situ, passive sampler technique of revealing diffusive gradients in thin films (DGT) encompassed the special resin, based on referenced extraction and coloration-computer imaging densitometry, were employed to obtain labile MeHg, Fe, and S concentrations at high resolution. The results indicate that larval bioturbation during the initial period of the experiment could diminish bioavailable MeHg concentrations and change the diffusion direction of MeHg fluxes. However, this inhibitive effect on MeHg concentrations ceased with larvae eclosion. Compared to bioturbation, wind fluctuation exerted slow but sustained inhibition on MeHg release. Furthermore, the eight parameters (dissolved organic carbon (DOC), DO, labile Fe and S concentrations, pH, sulfate-reducing bacteria (SRB) abundance in sediment, oxidation-reduction potential (ORP) and EC) could explain more of variation in MeHg concentrations which indicated by the canonical correspondence analysis. And these eight parameters manifest higher explanatory power for MeHg distributed in newly formed sediment. More notably, the comparison results of the multiple and simple regression directly demonstrated the DOC was the fundamental and robust factor to control the MeHg variation in the freshwater ecosystem.
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Affiliation(s)
- Peifang Wang
- Key Laboratory of Integrated Regulation and Resource Development of Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China.
| | - Yu Yao
- Key Laboratory of Integrated Regulation and Resource Development of Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China.
| | - Chao Wang
- Key Laboratory of Integrated Regulation and Resource Development of Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
| | - Jun Hou
- Key Laboratory of Integrated Regulation and Resource Development of Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
| | - Jin Qian
- Key Laboratory of Integrated Regulation and Resource Development of Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
| | - Lingzhan Miao
- Key Laboratory of Integrated Regulation and Resource Development of Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
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402
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De León KB, Zane GM, Trotter VV, Krantz GP, Arkin AP, Butland GP, Walian PJ, Fields MW, Wall JD. Unintended Laboratory-Driven Evolution Reveals Genetic Requirements for Biofilm Formation by Desulfovibrio vulgaris Hildenborough. mBio 2017; 8:e01696-17. [PMID: 29042504 PMCID: PMC5646257 DOI: 10.1128/mbio.01696-17] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 09/18/2017] [Indexed: 12/28/2022] Open
Abstract
Biofilms of sulfate-reducing bacteria (SRB) are of particular interest as members of this group are culprits in corrosion of industrial metal and concrete pipelines as well as being key players in subsurface metal cycling. Yet the mechanism of biofilm formation by these bacteria has not been determined. Here we show that two supposedly identical wild-type cultures of the SRB Desulfovibrio vulgaris Hildenborough maintained in different laboratories have diverged in biofilm formation. From genome resequencing and subsequent mutant analyses, we discovered that a single nucleotide change within DVU1017, the ABC transporter of a type I secretion system (T1SS), was sufficient to eliminate biofilm formation in D. vulgaris Hildenborough. Two T1SS cargo proteins were identified as likely biofilm structural proteins, and the presence of at least one (with either being sufficient) was shown to be required for biofilm formation. Antibodies specific to these biofilm structural proteins confirmed that DVU1017, and thus the T1SS, is essential for localization of these adhesion proteins on the cell surface. We propose that DVU1017 is a member of the lapB category of microbial surface proteins because of its phenotypic similarity to the adhesin export system described for biofilm formation in the environmental pseudomonads. These findings have led to the identification of two functions required for biofilm formation in D. vulgaris Hildenborough and focus attention on the importance of monitoring laboratory-driven evolution, as phenotypes as fundamental as biofilm formation can be altered.IMPORTANCE The growth of bacteria attached to a surface (i.e., biofilm), specifically biofilms of sulfate-reducing bacteria, has a profound impact on the economy of developed nations due to steel and concrete corrosion in industrial pipelines and processing facilities. Furthermore, the presence of sulfate-reducing bacteria in oil wells causes oil souring from sulfide production, resulting in product loss, a health hazard to workers, and ultimately abandonment of wells. Identification of the required genes is a critical step for determining the mechanism of biofilm formation by sulfate reducers. Here, the transporter by which putative biofilm structural proteins are exported from sulfate-reducing Desulfovibrio vulgaris Hildenborough cells was discovered, and a single nucleotide change within the gene coding for this transporter was found to be sufficient to completely stop formation of biofilm.
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Affiliation(s)
- Kara B De León
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
| | - Grant M Zane
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
| | - Valentine V Trotter
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Gregory P Krantz
- Department of Microbiology and Immunology, Montana State University, Bozeman, Montana, USA
- Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA
| | - Adam P Arkin
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Bioengineering, University of California, Berkeley, California, USA
| | - Gareth P Butland
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Peter J Walian
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Matthew W Fields
- Department of Microbiology and Immunology, Montana State University, Bozeman, Montana, USA
- Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA
| | - Judy D Wall
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
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403
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Kuss J, Cordes F, Mohrholz V, Nausch G, Naumann M, Krüger S, Schulz-Bull DE. The Impact of the Major Baltic Inflow of December 2014 on the Mercury Species Distribution in the Baltic Sea. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:11692-11700. [PMID: 28885012 DOI: 10.1021/acs.est.7b03011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The Baltic Sea is a marginal sea characterized by stagnation periods of several years. Oxygen consumption in its deep waters leads to the buildup of sulfide from sulfate reduction. Some of the microorganisms responsible for these processes also transform reactive ionic mercury to neurotoxic methylmercury. Episodic inflows of oxygenated saline water from the North Sea temporally re-establish oxic life in deep waters of the Baltic Sea. Thus, this sea is an especially important region to better understand mercury species distributions in connection with variable redox conditions. Mercury species were measured on three Baltic Sea campaigns, during the preinflow, ongoing inflow, and subsiding inflow of water, respectively, to the central basin. The inflowing water caused the removal of total mercury by 600 nmol m-2 and of methylmercury by 214 nmol m-2 in the Gotland Deep, probably via attachment of the mercury compounds to sinking particles. It appears likely that the consequences of the oxygenation of Baltic Sea deep waters, which are the coprecipitation of mercury species and the resettlement of the oxic deep waters, could lead to the enhanced transfer of accumulated mercury and methylmercury to the planktonic food chain and finally to fish.
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Affiliation(s)
- Joachim Kuss
- Department of Marine Chemistry, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
| | - Florian Cordes
- Department of Marine Chemistry, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
| | - Volker Mohrholz
- Department of Physical Oceanography and Measurement & Instrumentation, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
| | - Günther Nausch
- Department of Marine Chemistry, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
| | - Michael Naumann
- Department of Physical Oceanography and Measurement & Instrumentation, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
| | - Siegfried Krüger
- Department of Physical Oceanography and Measurement & Instrumentation, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
| | - Detlef E Schulz-Bull
- Department of Marine Chemistry, Leibniz Institute for Baltic Sea Research (IOW) , Seestrasse 15, D-18119 Rostock-Warnemünde, Germany
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404
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Soerensen AL, Schartup AT, Skrobonja A, Björn E. Organic matter drives high interannual variability in methylmercury concentrations in a subarctic coastal sea. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017. [PMID: 28646796 DOI: 10.1016/j.envpol.2017.06.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Levels of neurotoxic methylmercury (MeHg) in phytoplankton are strongly associated with water MeHg concentrations. Because uptake by phytoplankton is the first and largest step of bioaccumulation in aquatic food webs many studies have investigated factors driving seasonal changes in water MeHg concentrations. Organic matter (OM) is widely accepted as an important driver of MeHg production and uptake by phytoplankton but is also known for strong interannual variability in concentration and composition within systems. In this study, we explore the role of OM on spatial and interannual variability of MeHg in a subarctic coastal sea, the northern Baltic Sea. Using MeHg (2014: 80 ± 25 fM; 2015: <LOD; 2016: 21 ± 9 fM) and OM measurements during late summer/early fall, we find that dissolved organic carbon (DOC) and humic matter content explain 60% of MeHg variability. We find that while labile DOC increases MeHg levels in the water, humic content reduces it. We propose that the positive association between MeHg and labile DOC shows that labile DOC is a proxy for OM remineralization rate in nearshore and offshore waters. This is consistent with other studies finding that in situ MeHg production in the water column occurs during OM remineralization. The negative association between water humic content and MeHg concentration is most likely due to humic matter decreasing inorganic mercury (HgII) bioavailability to methylating microbes. With these relationships, we develop a statistical model and use it to calculate MeHg concentrations in late summer nearshore and offshore waters between 2006 and 2016 using measured values for water DOC and humic matter content. We find that MeHg concentrations can vary by up to an order of magnitude between years, highlighting the importance of considering interannual variability in water column MeHg concentrations when interpreting both short and long term MeHg trends in biota.
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Affiliation(s)
- A L Soerensen
- Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden.
| | - A T Schartup
- Harvard University, John A. Paulson School of Engineering and Applied Sciences, Cambridge MA, USA
| | - A Skrobonja
- Umeå University, Department of Chemistry, Umeå, Sweden
| | - E Björn
- Umeå University, Department of Chemistry, Umeå, Sweden
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405
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Reid MC, Maillard J, Bagnoud A, Falquet L, Le Vo P, Bernier-Latmani R. Arsenic Methylation Dynamics in a Rice Paddy Soil Anaerobic Enrichment Culture. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:10546-10554. [PMID: 28825798 DOI: 10.1021/acs.est.7b02970] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Methylated arsenic (As) species represent a significant fraction of the As accumulating in rice grains, and there are geographic patterns in the abundance of methylated arsenic in rice that are not understood. The microorganisms driving As biomethylation in paddy environments, and thus the soil conditions conducive to the accumulation of methylated arsenic, are unknown. We tested the hypothesis that sulfate-reducing bacteria (SRB) are key drivers of arsenic methylation in metabolically versatile mixed anaerobic enrichments from a Mekong Delta paddy soil. We used molybdate and monofluorophosphate as inhibitors of sulfate reduction to evaluate the contribution of SRB to arsenic biomethylation, and developed degenerate primers for the amplification of arsM genes to identify methylating organisms. Enrichment cultures converted 63% of arsenite into methylated products, with dimethylarsinic acid as the major product. While molybdate inhibited As biomethylation, this effect was unrelated to its inhibition of sulfate reduction and instead inhibited the methylation pathway. Based on arsM sequences and the physiological response of cultures to media conditions, we propose that amino acid fermenting organisms are potential drivers of As methylation in the enrichments. The lack of a demethylating capacity may have contributed to the robust methylation efficiencies in this mixed culture.
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Affiliation(s)
- Matthew C Reid
- Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland
| | - Julien Maillard
- Laboratory for Environmental Biotechnology, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland
| | - Alexandre Bagnoud
- Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland
| | - Leia Falquet
- Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland
| | - Phu Le Vo
- Ho Chi Minh City University of Technology - VNU HCM , Ho Chi Minh City, Vietnam
| | - Rizlan Bernier-Latmani
- Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland
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406
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Zhao L, Chen H, Lu X, Lin H, Christensen GA, Pierce EM, Gu B. Contrasting Effects of Dissolved Organic Matter on Mercury Methylation by Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:10468-10475. [PMID: 28806071 DOI: 10.1021/acs.est.7b02518] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Natural dissolved organic matter (DOM) affects mercury (Hg) redox reactions and anaerobic microbial methylation in the environment. Several studies have shown that DOM can enhance Hg methylation, especially under sulfidic conditions, whereas others show that DOM inhibits Hg methylation due to strong Hg-DOM complexation. In this study, we investigated and compared the effects of DOM on Hg methylation by an iron-reducing bacterium Geobacter sulfurreducens PCA and a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under nonsulfidic conditions. The methylation experiment was performed with washed cells either in the absence or presence of DOM or glutathione, both of which form strong complexes with Hg via thiol-functional groups. DOM was found to greatly inhibit Hg methylation by G. Sulfurreducens PCA but enhance Hg methylation by D. desulfuricans ND132 cells with increasing DOM concentration. These strain-dependent opposing effects of DOM were also observed with glutathione, suggesting that thiols in DOM likely played an essential role in affecting microbial Hg uptake and methylation. Additionally, DOM and glutathione greatly decreased Hg sorption by G. sulfurreducens PCA but showed little effect on D. desulfuricans ND132 cells, demonstrating that ND132 has a higher affinity to sorb or take up Hg than the PCA strain. These observations indicate that DOM effects on Hg methylation are bacterial strain specific, depend on the DOM:Hg ratio or site-specific conditions, and may thus offer new insights into the role of DOM in methylmercury production in the environment.
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Affiliation(s)
- Linduo Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Hongmei Chen
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Hui Lin
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Geoff A Christensen
- Biosciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Eric M Pierce
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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407
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Narváez DM, Groot H, Diaz SM, Palma RM, Muñoz N, Cros MP, Hernández-Vargas H. Oxidative stress and repetitive element methylation changes in artisanal gold miners occupationally exposed to mercury. Heliyon 2017; 3:e00400. [PMID: 28948237 PMCID: PMC5602780 DOI: 10.1016/j.heliyon.2017.e00400] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 08/08/2017] [Accepted: 08/30/2017] [Indexed: 12/22/2022] Open
Abstract
Mercury (Hg) exposure is a public health concern due to its persistence in the environment and its high toxicity. Such toxicity has been associated with the generation of oxidative stress in occupationally exposed subjects, such as artisanal gold miners. In this study, we characterize occupational exposure to Hg by measuring blood, urine and hair levels, and investigate oxidative stress and DNA methylation associated with gold mining. To do this, samples from 53 miners and 36 controls were assessed. We show higher levels of oxidative stress marker 8-OHdG in the miners. Differences in LINE1 and Alu(Yb8) DNA methylation between gold miners and control group are present in peripheral blood leukocytes. LINE1 methylation is positively correlated with 8-OHdG levels, while XRCC1 and LINE1 methylation are positively correlated with Hg levels. These results suggest an effect of Hg on oxidative stress and DNA methylation in gold miners that may have an impact on miners' health.
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Affiliation(s)
- Diana M. Narváez
- Human Genetics Laboratory. Universidad de los Andes. Bogotá, Colombia
- Instituto Nacional de Salud (INS). Bogotá, Colombia
- Epigenetics Group. International Agency for Research on Cancer (IARC). Lyon, France
| | - Helena Groot
- Human Genetics Laboratory. Universidad de los Andes. Bogotá, Colombia
| | | | | | | | - Marie-Pierre Cros
- Epigenetics Group. International Agency for Research on Cancer (IARC). Lyon, France
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408
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Ma M, Du H, Wang D, Kang S, Sun T. Biotically mediated mercury methylation in the soils and sediments of Nam Co Lake, Tibetan Plateau. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017; 227:243-251. [PMID: 28475977 DOI: 10.1016/j.envpol.2017.04.037] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 04/10/2017] [Accepted: 04/17/2017] [Indexed: 05/16/2023]
Abstract
Previous research found that methylmercury (MeHg) levels in the fish of Nam Co Lake of Tibetan Plateau were remarkably higher than those obtained from Hg-polluted areas, probably indicating a stronger biomagnification and higher MeHg transfer efficient. Until now, little research has been carried out on the distribution of Hg methylators here, which maybe important to explain the higher fish MeHg levels. MeHg concentrations were remarkably different between the soil and sediment samples in both seasons. Illumina MiSeq sequencing of 16S rRNA gene amplicons showed that species richness estimates of the soil and sediment samples were both quite low based on Ace and Chao estimators. Community composition differed between the sediment and bank soil samples. DsrB gene quantities were relatively high, but the hgcA quantities were low, which indicated that most of the SRB found may not be Hg methylators. It is predicted that strains in Ruminococcaceae may be the main Hg methylators in the sediment, whose Hg methylation abilities were lower comparing with those in δ-proteobacteria. The relative abundances of the genera that contain known Hg methylators were all below 0.8%, which may explain the relatively lower levels of MeHg in the sediment of Nam Co Lake compared to other aquatic systems. This may also reflect that Hg methylators were relatively rare among most clades and abiotically regulated Hg methylation may exert relatively more important role here.
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Affiliation(s)
- Ming Ma
- College of Resources and Environment, Southwest University, Chongqing 400715, China; Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing 400715, China
| | - Hongxia Du
- College of Resources and Environment, Southwest University, Chongqing 400715, China
| | - Dingyong Wang
- College of Resources and Environment, Southwest University, Chongqing 400715, China; Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing 400715, China.
| | - Shichang Kang
- Northeast Institute of Eco-Environment and Resources, CAS, Lanzhou, 730000, China.
| | - Tao Sun
- College of Resources and Environment, Southwest University, Chongqing 400715, China; Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing 400715, China
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409
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Llop S, Tran V, Ballester F, Barbone F, Sofianou-Katsoulis A, Sunyer J, Engström K, Alhamdow A, Love TM, Watson GE, Bustamante M, Murcia M, Iñiguez C, Shamlaye CF, Rosolen V, Mariuz M, Horvat M, Tratnik JS, Mazej D, van Wijngaarden E, Davidson PW, Myers GJ, Rand MD, Broberg K. CYP3A genes and the association between prenatal methylmercury exposure and neurodevelopment. ENVIRONMENT INTERNATIONAL 2017; 105:34-42. [PMID: 28500872 PMCID: PMC5517297 DOI: 10.1016/j.envint.2017.04.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2016] [Revised: 04/26/2017] [Accepted: 04/26/2017] [Indexed: 05/31/2023]
Abstract
BACKGROUND Results on the association between prenatal exposure to methylmercury (MeHg) and child neuropsychological development are heterogeneous. Underlying genetic differences across study populations could contribute to this varied response to MeHg. Studies in Drosophila have identified the cytochrome p450 3A (CYP3A) family as candidate MeHg susceptibility genes. OBJECTIVES We evaluated whether genetic variation in CYP3A genes influences the association between prenatal exposure to MeHg and child neuropsychological development. METHODS The study population included 2639 children from three birth cohort studies: two subcohorts in Seychelles (SCDS) (n=1160, 20 and 30months of age, studied during the years 2001-2012), two subcohorts from Spain (INMA) (n=625, 14months of age, 2003-2009), and two subcohorts from Italy and Greece (PHIME) (n=854, 18months of age, 2006-2011). Total mercury, as a surrogate of MeHg, was analyzed in maternal hair and/or cord blood samples. Neuropsychological development was evaluated using Bayley Scales of Infant Development (BSID). Three functional polymorphisms in the CYP3A family were analyzed: rs2257401 (CYP3A7), rs776746 (CYP3A5), and rs2740574 (CYP3A4). RESULTS There was no association between CYP3A polymorphisms and cord mercury concentrations. The scores for the BSID mental scale improved with increasing cord blood mercury concentrations for carriers of the most active alleles (β[95% CI]:=2.9[1.53,4.27] for CYP3A7 rs2257401 GG+GC, 2.51[1.04,3.98] for CYP3A5 rs776746 AA+AG and 2.31[0.12,4.50] for CYP3A4 rs2740574 GG+AG). This association was near the null for CYP3A7 CC, CYP3A5 GG and CYP3A4 AA genotypes. The interaction between the CYP3A genes and total mercury was significant (p<0.05) in European cohorts only. CONCLUSIONS Our results suggest that the polymorphisms in CYP3A genes may modify the response to dietary MeHg exposure during early life development.
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Affiliation(s)
- Sabrina Llop
- Epidemiology and Environmental Health Joint Research Unit, FISABIO-Universitat Jaume I-Universitat de València, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Av. Monforte de Lemos, 3-5. Pabellón 11, 28029 Madrid, Spain
| | - Van Tran
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Ferran Ballester
- Epidemiology and Environmental Health Joint Research Unit, FISABIO-Universitat Jaume I-Universitat de València, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Av. Monforte de Lemos, 3-5. Pabellón 11, 28029 Madrid, Spain
| | - Fabio Barbone
- Department of Medical and Biological Sciences, University of Udine, via Colugna 50, 33100 Udine, Italy; Institute for Maternal and Child Health IRCCS "Burlo Garofolo", via dell'Istria 65/1, 34137 Trieste, Italy
| | | | - Jordi Sunyer
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Av. Monforte de Lemos, 3-5. Pabellón 11, 28029 Madrid, Spain; ISGlobal, Centre for Research in Environmental Epidemiology (CREAL), Av. Aiguader 88, 08003 Barcelona, Spain; IMIM (Hospital del Mar Medical Research Institute), Av. Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), Av. Aiguader 88, 08003 Barcelona, Spain
| | - Karin Engström
- Division of Occupational and Environmental Medicine, Lund University, 22185 Lund, Sweden
| | - Ayman Alhamdow
- Institute of Environmental Medicine, Karolinska Institutet, Nobels väg 13, 17177 Stockholm, Sweden
| | - Tanzy M Love
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Gene E Watson
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Mariona Bustamante
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Av. Monforte de Lemos, 3-5. Pabellón 11, 28029 Madrid, Spain; ISGlobal, Centre for Research in Environmental Epidemiology (CREAL), Av. Aiguader 88, 08003 Barcelona, Spain; IMIM (Hospital del Mar Medical Research Institute), Av. Aiguader 88, 08003 Barcelona, Spain; Genomics and Disease Group, Bioinformatics and Genomics Program, Centre for Genomic Regulation (CRG), Av. Aiguader 88, 08003 Barcelona, Spain
| | - Mario Murcia
- Epidemiology and Environmental Health Joint Research Unit, FISABIO-Universitat Jaume I-Universitat de València, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Av. Monforte de Lemos, 3-5. Pabellón 11, 28029 Madrid, Spain
| | - Carmen Iñiguez
- Epidemiology and Environmental Health Joint Research Unit, FISABIO-Universitat Jaume I-Universitat de València, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Av. Monforte de Lemos, 3-5. Pabellón 11, 28029 Madrid, Spain
| | | | - Valentina Rosolen
- Department of Medical and Biological Sciences, University of Udine, via Colugna 50, 33100 Udine, Italy
| | - Marika Mariuz
- Department of Medical and Biological Sciences, University of Udine, via Colugna 50, 33100 Udine, Italy
| | - Milena Horvat
- Department of Environmental Sciences, Jozef Stefan Institute, Jamova cesta 39, Si-1000 Ljubljana, Slovenia
| | - Janja S Tratnik
- Department of Environmental Sciences, Jozef Stefan Institute, Jamova cesta 39, Si-1000 Ljubljana, Slovenia
| | - Darja Mazej
- Department of Environmental Sciences, Jozef Stefan Institute, Jamova cesta 39, Si-1000 Ljubljana, Slovenia
| | - Edwin van Wijngaarden
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Philip W Davidson
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Gary J Myers
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Matthew D Rand
- University of Rochester Medical Center, School of Medicine and Dentistry, 601 Elmwood Ave, Box 671, Rochester, NY 14642, USA
| | - Karin Broberg
- Institute of Environmental Medicine, Karolinska Institutet, Nobels väg 13, 17177 Stockholm, Sweden.
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410
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Gentès S, Taupiac J, Colin Y, André JM, Guyoneaud R. Bacterial periphytic communities related to mercury methylation within aquatic plant roots from a temperate freshwater lake (South-Western France). ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2017; 24:19223-19233. [PMID: 28664497 DOI: 10.1007/s11356-017-9597-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Accepted: 06/20/2017] [Indexed: 06/07/2023]
Abstract
Macrophyte floating roots are considered as hotspots for methylmercury (MeHg) production in aquatic ecosystems through microbial activity. Nevertheless, very little is known about periphyton bacterial communities and mercury (Hg) methylators in such ecological niches. The ability to methylate inorganic Hg is broadly distributed among prokaryotes; however, sulfate-reducers have been reported to be the most important MeHg producers in macrophyte floating roots. In the present work, the periphyton bacterial communities colonizing Ludwigia sp. floating roots were investigated through molecular methods. Among the 244 clones investigated, anaerobic microorganisms associated with the sulfur biogeochemical cycle were identified. Notably, members of the sulfur-oxidizing prokaryotes and the anoxygenic, purple non-sulfur bacteria (Rhodobacteraceae, Comamonadaceae, Rhodocyclaceae, Hyphomicrobiaceae) and the sulfate reducers (Desulfobacteraceae, Syntrophobacteraceae, and Desulfobulbaceae) were detected. In addition, 15 sulfate-reducing strains related to the Desulfovibrionaceae family were isolated and their Hg-methylation capacity was tested using a biosensor. The overall results confirmed that Hg methylation is a strain-specific process since the four strains identified as new Hg-methylators were closely related to non-methylating isolates. This study highlights the potential involvement of periphytic bacteria in Hg methylation when favorable environmental conditions are present in such ecological micro-niches.
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Affiliation(s)
- Sophie Gentès
- Equipe Environnement et Microbiologie, UMR IPREM5254 Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France.
- Université de Bordeaux, EPOC, UMR CNRS 5805, 33120, Arcachon, France.
| | - Julie Taupiac
- Equipe Environnement et Microbiologie, UMR IPREM5254 Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France
| | - Yannick Colin
- Equipe Environnement et Microbiologie, UMR IPREM5254 Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France
| | - Jean-Marc André
- Equipe CIH, IMS UMR 5218, Ecole Nationale Supérieure de Cognitique, 109 Avenue Roul, 33400, Talence, France
| | - Rémy Guyoneaud
- Equipe Environnement et Microbiologie, UMR IPREM5254 Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France
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411
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Amin A, Latif Z. Cloning, Expression, Isotope Labeling, and Purification of Transmembrane Protein MerF from Mercury Resistant Enterobacter sp. AZ-15 for NMR Studies. Front Microbiol 2017; 8:1250. [PMID: 28736549 PMCID: PMC5500634 DOI: 10.3389/fmicb.2017.01250] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Accepted: 06/21/2017] [Indexed: 11/15/2022] Open
Abstract
Mercury resistant (HgR) Enterobacter sp. AZ-15 was isolated from heavy metal polluted industrial wastewater samples near to districts Kasur and Sheikhupura, Pakistan. 16S rDNA ribotyping and phylogentic analysis showed 98% homology with already reported Enterobacter species. The merF gene encoding transmembrane protein-MerF was amplified from genomic DNA and ligated into pET31b+ vector using restriction endonucleases, SphI and XhoI. The genetic codons of merF gene encoding cysteine residues were mutated into codons, translating into serine residues by site-directed mutagenesis. Ketosteroid isomerase (KSI), a fusion tag which is present in pET31b+ vector, was used in the expression of merFm gene. KSI was used to drive the target peptide (MerFm) into inclusion bodies so that the peptide yield and purity were increased. The stable plasmid pET31b+:merFm was transformed into C43(DE3) E.coli cells. The high expression of uniformly 15N isotopically labeled-MerFm protein was induced with 1 mM IPTG. The purification of 15N-MerFm recombinant protein by Ni-NTA and size exclusion chromatography involved an unfolding/refolding procedure. The two-dimensional HSQC NMR spectra of MerFm protein showed the purity and correct number of resonances for each amide. 1H-15N HSQC NMR experiment also confirmed that no modification of the tryptophan residue occurred during cyanogen bromide cleavage. A small scale reservoir of Luria Bertani (LB) medium supplemented with 20 μg/ml of HgCl2 showed 90% detoxification of Hg by Enterobacter sp. AZ-15. The accumulation of Hg on the cell surface of this strain was visualized by scanning electron microscopy (SEM) which confirmed its potential use in Hg-bioremediation.
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Affiliation(s)
- Aatif Amin
- Department of Microbiology and Molecular Genetics, University of the PunjabLahore, Pakistan
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412
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Cesário R, Hintelmann H, Mendes R, Eckey K, Dimock B, Araújo B, Mota AM, Canário J. Evaluation of mercury methylation and methylmercury demethylation rates in vegetated and non-vegetated saltmarsh sediments from two Portuguese estuaries. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017; 226:297-307. [PMID: 28390703 DOI: 10.1016/j.envpol.2017.03.075] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 02/23/2017] [Accepted: 03/31/2017] [Indexed: 06/07/2023]
Abstract
Neurotoxic methylmercury (MMHg) is formed from inorganic divalent mercury (Hg2+). However, it is poorly understood to what extent different mercury (Hg) pools contribute to existent MMHg levels. In this study, ambient concentrations of total Hg (THg) and MMHg as well as rates of methylation and demethylation were measured simultaneously in sediments with and without salt-marsh plant vegetation, which were collected in Guadiana and Tagus estuaries, Portugal. Concurrent processes of Hg methylation and MMHg demethylation were directly monitored and compared by spiking sediments cores with stable isotope tracers of 199Hg2+ and CH3201Hg+ followed by gas chromatographic separation and isotope-specific detection using inductively coupled plasma mass spectrometry. Compared to the Guadiana estuary, where concentrations were comparatively low, THg and MMHg levels varied between vegetated and non-vegetated sediments collected at the Rosário site (ROS) of the Tagus estuary. Methylation (KM) and demethylation rates (KD) were also different between estuaries being dependent on the presence of vegetation. In addition, the type of macrophyte species influenced KM and KD values. In fact, the highest KM value was found in Sarcocornia fruticosa vegetated sediments at the Castro Marim site in Guadiana (CM, 0.160 day-1) and the lowest KM was observed in non-vegetated sediments at the Alcochete site in Tagus (ALC, 0.009 day-1). KD varied by a factor of three among sites with highest rates of demethylation observed in non-vegetated sediments in Guadiana (12 ± 1.3 day-1, corresponding to a half-life of 1.4 ± 0.2 h). This study clearly shows that the presence of vegetation in sediments favors the formation of MMHg. Moreover, this effect might be site specific and further studies are needed to confirm the findings reported here.
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Affiliation(s)
- Rute Cesário
- Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1, 1049-001 Lisboa, Portugal; IPMA-Instituto Português do Mar e Atmosfera, Av. Brasília, 1449-006 Lisboa, Portugal
| | - Holger Hintelmann
- Water Quality Centre, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 0G2, Canada
| | - Ricardo Mendes
- IPMA-Instituto Português do Mar e Atmosfera, Av. Brasília, 1449-006 Lisboa, Portugal
| | - Kevin Eckey
- Institute of Inorganic and Analytical Chemistry, University of Muenster, Schlossplatz 2, 48149 Munster, Germany
| | - Brian Dimock
- Water Quality Centre, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 0G2, Canada
| | - Beatriz Araújo
- Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense, Av. Alberto Lamego, 2000, Horto, Campus dos Goytacazes, Rio de Janeiro, Brazil
| | - Ana Maria Mota
- Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1, 1049-001 Lisboa, Portugal
| | - João Canário
- Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1, 1049-001 Lisboa, Portugal.
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413
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Clark IC, Abate AR. Finding a helix in a haystack: nucleic acid cytometry with droplet microfluidics. LAB ON A CHIP 2017; 17:2032-2045. [PMID: 28540956 PMCID: PMC6005652 DOI: 10.1039/c7lc00241f] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Nucleic acids encode the information of life, programming cellular functions and dictating many biological outcomes. Differentiating between cells based on their nucleic acid programs is, thus, a powerful way to unravel the genetic bases of many phenotypes. This is especially important considering that most cells exist in heterogeneous populations, requiring them to be isolated before they can be studied. Existing flow cytometry techniques, however, are unable to reliably recover specific cells based on nucleic acid content. Nucleic acid cytometry is a new field built on droplet microfluidics that allows robust identification, sorting, and sequencing of cells based on specific nucleic acid biomarkers. This review highlights applications that immediately benefit from the approach, biological questions that can be addressed for the first time with it, and considerations for building successful workflows.
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Affiliation(s)
- Iain C Clark
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, USA.
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414
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Lu X, Gu W, Zhao L, Farhan Ul Haque M, DiSpirito AA, Semrau JD, Gu B. Methylmercury uptake and degradation by methanotrophs. SCIENCE ADVANCES 2017; 3:e1700041. [PMID: 28580426 PMCID: PMC5451197 DOI: 10.1126/sciadv.1700041] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 03/30/2017] [Indexed: 05/22/2023]
Abstract
Methylmercury (CH3Hg+) is a potent neurotoxin produced by certain anaerobic microorganisms in natural environments. Although numerous studies have characterized the basis of mercury (Hg) methylation, no studies have examined CH3Hg+ degradation by methanotrophs, despite their ubiquitous presence in the environment. We report that some methanotrophs, such as Methylosinus trichosporium OB3b, can take up and degrade CH3Hg+ rapidly, whereas others, such as Methylococcus capsulatus Bath, can take up but not degrade CH3Hg+. Demethylation by M. trichosporium OB3b increases with increasing CH3Hg+ concentrations but was abolished in mutants deficient in the synthesis of methanobactin, a metal-binding compound used by some methanotrophs, such as M. trichosporium OB3b. Furthermore, addition of methanol (>5 mM) as a competing one-carbon (C1) substrate inhibits demethylation, suggesting that CH3Hg+ degradation by methanotrophs may involve an initial bonding of CH3Hg+ by methanobactin followed by cleavage of the C-Hg bond in CH3Hg+ by the methanol dehydrogenase. This new demethylation pathway by methanotrophs indicates possible broader involvement of C1-metabolizing aerobes in the degradation and cycling of toxic CH3Hg+ in the environment.
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Affiliation(s)
- Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Wenyu Gu
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Linduo Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Muhammad Farhan Ul Haque
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Alan A. DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jeremy D. Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Corresponding author.
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415
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Boczulak SA, Vanderwel MC, Hall BD. Survey of mercury in boreal chorus frog (Pseudacris maculata) and wood frog (Rana sylvatica) tadpoles from wetland ponds in the Prairie Pothole Region of Canada. Facets (Ott) 2017. [DOI: 10.1139/facets-2016-0041] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Tadpoles are important prey items for many aquatic organisms and often represent the largest vertebrate biomass in many fishless wetland ecosystems. Neurotoxic mercury (Hg) can, at elevated levels, decrease growth, lower survival, and cause developmental instability in amphibians. We compared total Hg (THg) body burden and concentration in boreal chorus frog ( Pseudacris maculata) and wood frog ( Rana sylvatica) tadpoles. Overall, body burden and concentration were lower in boreal chorus frog tadpoles than wood frog tadpoles, as expected, because boreal chorus frog tadpoles consume at lower trophic levels. The variables species, stage, and mass explained 21% of total variation for body burden in our models but had negligible predictive ability for THg concentration. The vast majority of the remaining variation in both body burden and THg concentration was attributable to differences among ponds; tadpoles from ponds in three areas had considerably higher THg body burden and concentration. The pond-to-pond differences were not related to any water chemistry or physical parameter measured, and we assumed that differences in wetland geomorphology likely played an important role in determining Hg levels in tadpoles. This is the first report of Hg in frog tadpoles in the Prairie Pothole Region of North America.
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Affiliation(s)
- Stacy A. Boczulak
- Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
| | - Mark C. Vanderwel
- Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
| | - Britt D. Hall
- Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
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416
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Paranjape AR, Hall BD. Recent advances in the study of mercury methylation in aquatic systems. Facets (Ott) 2017. [DOI: 10.1139/facets-2016-0027] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
With increasing input of neurotoxic mercury to environments as a result of anthropogenic activity, it has become imperative to examine how mercury may enter biotic systems through its methylation to bioavailable forms in aquatic environments. Recent development of stable isotope-based methods in methylation studies has enabled a better understanding of the factors controlling methylation in aquatic systems. In addition, the identification and tracking of the hgcAB gene cluster, which is necessary for methylation, has broadened the range of known methylators and methylation-conducive environments. Study of abiotic factors in methylation with new molecular methods (the use of stable isotopes and genomic methods) has helped elucidate the confounding influences of many environmental factors, as these methods enable the examination of their direct effects instead of merely correlative observations. Such developments will be helpful in the finer characterization of mercury biogeochemical cycles, which will enable better predictions of the potential effects of climate change on mercury methylation in aquatic systems and, by extension, the threat this may pose to biota.
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Affiliation(s)
- Avnee R. Paranjape
- Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
| | - Britt D. Hall
- Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
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417
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Thomas SA, Gaillard JF. Cysteine Addition Promotes Sulfide Production and 4-Fold Hg(II)-S Coordination in Actively Metabolizing Escherichia coli. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:4642-4651. [PMID: 28353340 DOI: 10.1021/acs.est.6b06400] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The bacterial uptake of mercury(II), Hg(II), is believed to be energy-dependent and is enhanced by cysteine in diverse species of bacteria under aerobic and anaerobic conditions. To gain insight into this Hg(II) biouptake pathway, we have employed X-ray absorption spectroscopy (XAS) to investigate the relationship between exogenous cysteine, cellular metabolism, cellular localization, and Hg(II) coordination in aerobically respiring Escherichia coli (E. coli). We show that cells harvested in exponential growth phase consistently display mixtures of 2-fold and 4-fold Hg(II) coordination to sulfur (Hg-S2 and Hg-S4), with added cysteine enhancing Hg-S4 formation. In contrast, cells in stationary growth phase or cells treated with a protonophore causing a decrease in cellular ATP predominantly contain Hg-S2, regardless of cysteine addition. Our XAS results favor metacinnabar (β-HgS) as the Hg-S4 species, which we show is associated with both the cell envelope and cytoplasm. Additionally, we observe that added cysteine abiotically oxidizes to cystine and exponentially growing E. coli degrade high cysteine concentrations (100-1000 μM) into sulfide. Thermodynamic calculations confirm that cysteine-induced sulfide biosynthesis can promote the formation of dissolved and particulate Hg(II)-sulfide species. This report reveals new complexities arising in Hg(II) bioassays with cysteine and emphasizes the need for considering changes in chemical speciation as well as growth stage.
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Affiliation(s)
- Sara A Thomas
- Department of Civil and Environmental Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Jean-François Gaillard
- Department of Civil and Environmental Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States
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418
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Liem-Nguyen V, Skyllberg U, Björn E. Thermodynamic Modeling of the Solubility and Chemical Speciation of Mercury and Methylmercury Driven by Organic Thiols and Micromolar Sulfide Concentrations in Boreal Wetland Soils. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:3678-3686. [PMID: 28248107 DOI: 10.1021/acs.est.6b04622] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Boreal wetlands have been identified as environments in which inorganic divalent mercury (HgII) is transformed to methylmercury (MeHg) by anaerobic microbes. In order to understand this transformation and the mobility and transport of HgII and MeHg, factors and conditions in control of the solubility and chemical speciation of HgII and MeHg need to be clarified. Here we explore the ability of thermodynamic models to simulate measured solubility of HgII and MeHg in different types of boreal wetland soils. With the input of measured concentrations of MeHg, sulfide, eight low molecular mass thiols and thiol groups associated with natural organic matter (NOM), as determined by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and Hg LIII-edge extended X-ray absorption fine structure spectroscopy (EXAFS), the model could accurately predict porewater concentrations of MeHg in the wetlands. A similar model for HgII successfully predicted the average level of its concentration in the porewaters, but the variability among samples, driven mainly by the concentration of aqueous inorganic sulfide, was predicted to be larger than measurements. The smaller than predicted variability in HgII solubility is discussed in light of possible formation of colloidal HgS(s) passing the 0.22 μm filters used to define the aqueous phase. The chemical speciation of the solid/adsorbed and aqueous phases were dominated by NOM associated thiol complexes for MeHg and by an equal contribution from NOM associated thiols and HgS(s) for HgII.
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Affiliation(s)
- Van Liem-Nguyen
- Department of Chemistry, Umeå University , SE-901 87 Umeå, Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences , SE-901 83 Umeå, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University , SE-901 87 Umeå, Sweden
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419
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Selenocystine against methyl mercury cytotoxicity in HepG2 cells. Sci Rep 2017; 7:147. [PMID: 28273949 PMCID: PMC5428050 DOI: 10.1038/s41598-017-00231-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 02/15/2017] [Indexed: 12/25/2022] Open
Abstract
Methyl mercury (MeHg) is a highly toxic substance and the effect of selenium against MeHg toxicity is a hot topic. Until now, no related works have been reported from the view of the point of elemental speciation which is promising to study the mechanism at the molecular level. In this work, to reveal the effect of selenocystine (SeCys2) against MeHg cytotoxicity in HepG2 cells, a comprehensive analytical platform for speciation study of mercury and selenium in MeHg incubated or MeHg and SeCys2 co-incubated HepG2 cells was developed by integrating liquid chromatography (LC) - inductively coupled plasma mass spectrometry (ICP-MS) hyphenated techniques and chip-based pretreatment method. Interesting phenomenon was found that the co-incubation of MeHg with SeCys2 promoted the uptake of MeHg in HepG2 cells, but reduced the cytotoxicity of MeHg. Results obtained by ICP-MS based hyphenated techniques revealed a possible pathway for the incorporation and excretion of mercury species with the coexistence of SeCys2. The formation of MeHg and SeCys2 aggregation promotes the uptake of MeHg; majority of MeHg transforms into small molecular complexes (MeHg-glutathione (GSH) and MeHg-cysteine (Cys)) in HepG2 cells; and MeHg-GSH is the elimination species which results in reducing the cytotoxicity of MeHg.
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420
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Boyd ES, Yu RQ, Barkay T, Hamilton TL, Baxter BK, Naftz DL, Marvin-DiPasquale M. Effect of salinity on mercury methylating benthic microbes and their activities in Great Salt Lake, Utah. THE SCIENCE OF THE TOTAL ENVIRONMENT 2017; 581-582:495-506. [PMID: 28057343 DOI: 10.1016/j.scitotenv.2016.12.157] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Revised: 12/22/2016] [Accepted: 12/22/2016] [Indexed: 06/06/2023]
Abstract
Surface water and biota from Great Salt Lake (GSL) contain some of the highest documented concentrations of total mercury (THg) and methylmercury (MeHg) in the United States. In order to identify potential biological sources of MeHg and controls on its production in this ecosystem, THg and MeHg concentrations, rates of Hg(II)-methylation and MeHg degradation, and abundances and compositions of archaeal and bacterial 16 rRNA gene transcripts were determined in sediment along a salinity gradient in GSL. Rates of Hg(II)-methylation were inversely correlated with salinity and were at or below the limits of detection in sediment sampled from areas with hypersaline surface water. The highest rates of Hg(II)-methylation were measured in sediment with low porewater salinity, suggesting that benthic microbial communities inhabiting less saline environments are supplying the majority of MeHg in the GSL ecosystem. The abundance of 16S rRNA gene transcripts affiliated with the sulfate reducer Desulfobacterium sp. was positively correlated with MeHg concentrations and Hg(II)-methylation rates in sediment, indicating a potential role for this taxon in Hg(II)-methylation in low salinity areas of GSL. Reactive inorganic Hg(II) (a proxy used for Hg(II) available for methylation) and MeHg concentrations were inversely correlated with salinity. Thus, constraints imposed by salinity on Hg(II)-methylating populations and the availability of Hg(II) for methylation are inferred to result in higher MeHg production potentials in lower salinity environments. Benthic microbial MeHg degradation was also most active in lower salinity environments. Collectively, these results suggest an important role for sediment anoxia and microbial sulfate reducers in the production of MeHg in low salinity GSL sub-habitats and may indicate a role for salinity in constraining Hg(II)-methylation and MeHg degradation activities by influencing the availability of Hg(II) for methylation.
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Affiliation(s)
- Eric S Boyd
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, United States.
| | - Ri-Qing Yu
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ 08901, United States
| | - Tamar Barkay
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ 08901, United States
| | - Trinity L Hamilton
- Department of Biological Sciences, University of Cincinnati, Cincinnati, OH 45221, United States
| | - Bonnie K Baxter
- Department of Biology, Westminster College, Salt Lake City, UT 84105, United States
| | - David L Naftz
- United States Geological Survey, Helena, MT 59601, United States
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421
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Dharampal PS, Findlay RH. Mercury levels in largemouth bass (Micropterus salmoides) from regulated and unregulated rivers. CHEMOSPHERE 2017; 170:134-140. [PMID: 27984776 DOI: 10.1016/j.chemosphere.2016.11.162] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 11/29/2016] [Accepted: 11/30/2016] [Indexed: 06/06/2023]
Abstract
Within areas of comparable atmospheric mercury deposition rates methylmercury burden in largemouth bass populations vary significantly between regulated and unregulated rivers. To investigate if trophic dynamics strongly influenced pollutant body load, we sampled largemouth bass from two adjacent rivers, one regulated and one unregulated, and applied a suite of biochemical and stable isotope assays to compare their trophic dynamics. Total mercury burden in the bass from the unregulated Sipsey River (Elrod, AL, USA) and the regulated Black Warrior River (Demopolis, AL, USA) averaged 0.87 mg kg-1 and 0.19 mg kg-1 wet weight, respectively. For both populations, age, weight, and length were positively correlated with muscle mercury concentration. Compound specific stable isotope analysis of amino acids showed the trophic position of both populations was just under four. Quantitative and isotopic analysis of neutral lipid fatty acid of Sipsey River bass indicated a greater reliance upon the detrital component of the food web compared to Demopolis Reservoir bass which fed within the autochthonous, pelagic component of the food web. Since the close proximity of the rivers makes differences in atmospheric deposition unlikely and both populations had similar trophic position, our findings indicate that food web dynamics should be included among the factors that can strongly influence mercury concentration in fish.
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Affiliation(s)
- Prarthana S Dharampal
- Department of Biological Sciences, Box 870344, University of Alabama, Tuscaloosa, AL 35487, United States
| | - Robert H Findlay
- Department of Biological Sciences, Box 870344, University of Alabama, Tuscaloosa, AL 35487, United States.
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422
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Kabir KM, Ippolito SJ, Kandjani AE, Sabri YM, Bhargava SK. Nano-engineered surfaces for mercury vapor sensing: Current state and future possibilities. Trends Analyt Chem 2017. [DOI: 10.1016/j.trac.2016.12.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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423
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Bigham GN, Murray KJ, Masue-Slowey Y, Henry EA. Biogeochemical controls on methylmercury in soils and sediments: Implications for site management. INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT 2017; 13:249-263. [PMID: 27427265 DOI: 10.1002/ieam.1822] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Revised: 05/10/2016] [Accepted: 06/28/2016] [Indexed: 05/25/2023]
Abstract
Management of Hg-contaminated sites poses particular challenges because methylmercury (MeHg), a potent bio-accumulative neurotoxin, is formed in the environment, and concentrations are not generally predictable based solely on total Hg (THg) concentrations. In this review, we examine the state of knowledge regarding the chemical, biological, and physical controls on MeHg production and identify those most critical for contaminated site assessment and management. We provide a list of parameters to assess Hg-contaminated soils and sediments with regard to their potential to be a source of MeHg to biota and therefore a risk to humans and ecological receptors. Because some measurable geochemical parameters (e.g., DOC) can have opposing effects on Hg methylation, we recommend focusing first on factors that describe the potential for Hg bio-accumulation: site characteristics, Hg and MeHg concentrations, Hg availability, and microbial activity, where practical. At some sites, more detailed assessment of biogeochemistry may be required to develop a conceptual site model for remedial decision making. Integr Environ Assess Manag 2017;13:249-263. © 2016 SETAC.
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Bailey LT, Mitchell CPJ, Engstrom DR, Berndt ME, Coleman Wasik JK, Johnson NW. Influence of porewater sulfide on methylmercury production and partitioning in sulfate-impacted lake sediments. THE SCIENCE OF THE TOTAL ENVIRONMENT 2017; 580:1197-1204. [PMID: 28024742 DOI: 10.1016/j.scitotenv.2016.12.078] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 12/12/2016] [Accepted: 12/12/2016] [Indexed: 06/06/2023]
Abstract
In low-sulfate and sulfate-limited freshwater sediments, sulfate loading increases the production of methylmercury (MeHg), a potent and bioaccumulative neurotoxin. Sulfate loading to anoxic sediments leads to sulfide production that can inhibit mercury methylation, but this has not been commonly observed in freshwater lakes and wetlands. In this study, sediments were collected from sulfate-impacted, neutral pH, surface water bodies located downstream from ongoing and historic mining activities to examine how chronic sulfate loading produces porewater sulfide, and influences MeHg production and transport. Sediments were collected over two years, during several seasons from lakes with a wide range of overlying water sulfate concentration. Samples were characterized for in-situ solid phase and porewater MeHg, Hg methylation potentials via incubations with enriched stable Hg isotopes, and sulfur, carbon, and iron content and speciation. Porewater sulfide reflected historic sulfur loading and was strongly related to the extractable iron content of sediment. Overall, methylation potentials were consistent with the accumulation of MeHg on the solid phase, but both methylation potentials and MeHg were significantly lower at chronically sulfate-impacted sites with a low solid-phase Fe:S ratio. At these heavily sulfate-impacted sites that also contained elevated porewater sulfide, both MeHg production and partitioning are influenced: Hg methylation potentials and sediment MeHg concentrations are lower, but occasionally porewater MeHg concentrations in sediment are elevated, particularly in the spring. The dual role of sulfide as a ligand for inorganic mercury (decreasing bioavailability) and methylmercury (increasing partitioning into porewater) means that elucidating the role of iron and sulfur loads as they define porewater sulfide is key to understanding sulfate's influence on MeHg production and partitioning in sulfate-impacted freshwater sediment.
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Affiliation(s)
- Logan T Bailey
- Water Resources Science Program, University of Minnesota, United States
| | - Carl P J Mitchell
- Department of Physical and Environmental Sciences, University of Toronto Scarborough, Canada
| | - Daniel R Engstrom
- St. Croix Watershed Research Station, Science Museum of Minnesota, United States
| | - Michael E Berndt
- Minnesota Department of Natural Resources, Division of Lands and Minerals, United States
| | - Jill K Coleman Wasik
- St. Croix Watershed Research Station, Science Museum of Minnesota, United States
| | - Nathan W Johnson
- Water Resources Science Program, University of Minnesota, United States; Department of Civil Engineering, University of Minnesota Duluth, United States.
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425
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Molecular composition of organic matter controls methylmercury formation in boreal lakes. Nat Commun 2017; 8:14255. [PMID: 28181492 PMCID: PMC5309796 DOI: 10.1038/ncomms14255] [Citation(s) in RCA: 148] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 12/13/2016] [Indexed: 11/08/2022] Open
Abstract
A detailed understanding of the formation of the potent neurotoxic methylmercury is needed to explain the large observed variability in methylmercury levels in aquatic systems. While it is known that organic matter interacts strongly with mercury, the role of organic matter composition in the formation of methylmercury in aquatic systems remains poorly understood. Here we show that phytoplankton-derived organic compounds enhance mercury methylation rates in boreal lake sediments through an overall increase of bacterial activity. Accordingly, in situ mercury methylation defines methylmercury levels in lake sediments strongly influenced by planktonic blooms. In contrast, sediments dominated by terrigenous organic matter inputs have far lower methylation rates but higher concentrations of methylmercury, suggesting that methylmercury was formed in the catchment and imported into lakes. Our findings demonstrate that the origin and molecular composition of organic matter are critical parameters to understand and predict methylmercury formation and accumulation in boreal lake sediments. Neurotoxic methylmercury can be found in high levels in aquatic systems, but the role of organic matter in methylmercury formation is not well understood. Here, Bravo et al. show that plankton-derived organic compounds enhance formation rates in boreal lakes.
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426
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Vitamin B 12 in the spotlight again. Curr Opin Chem Biol 2017; 37:63-70. [PMID: 28167430 DOI: 10.1016/j.cbpa.2017.01.013] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 01/07/2017] [Accepted: 01/17/2017] [Indexed: 11/21/2022]
Abstract
The ability of cobalamin to coordinate different upper axial ligands gives rise to a diversity of reactivity. Traditionally, adenosylcobalamin is associated with radical-based rearrangements, and methylcobalamin with methyl cation transfers. Recently, however, a new role for adenosylcobalamin has been discovered as a light sensor, and a methylcobalamin-dependent enzyme has been identified that is suggested to transfer a methyl anion. Additionally, recent studies have provided a wealth of new information about a third class of cobalamin-dependent enzymes that do not appear to use an upper ligand. They function in reductive dehalogenations and epoxide reduction reactions. Finally, mechanistic details are beginning to emerge about the cobalamin-dependent S-adenosylmethionine radical enzyme superfamily for which the role of cobalamin has been largely enigmatic.
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427
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Du H, Ma M, Sun T, Dai X, Yang C, Luo F, Wang D, Igarashi Y. Mercury-methylating genes dsrB and hgcA in soils/sediments of the Three Gorges Reservoir. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2017; 24:5001-5011. [PMID: 28000068 DOI: 10.1007/s11356-016-8213-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 12/06/2016] [Indexed: 05/04/2023]
Abstract
Previous research found that the water-level fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR) was an Hg-sensitive area. However, little research has been conducted on the distribution of Hg-methylating microorganisms in this area. The goal of this research was to provide an initial description of the distribution of the dsrB (for sulfate-reducing bacteria) and hgcA (one gene confirmed for Hg methylation) genes. Different types of soil were selected to analyze the abundance of the dsrB and hgcA in different periods, in inundated soil (SI, ≤155 m, which becomes sediment during the wet period, SS) and in non-inundated soil (≥175 m, SN) from Shibao, a typical WLFZ of the TGR. A significant positive correlation was observed between dsrB and hgcA abundance and MeHg concentrations, suggesting that microorganisms with these genes contribute to Hg methylation. Principal component analysis (PCA) indicated that dsrB diversity was highest in SI, followed by SS; SS had the highest diversity of hcgA. Six phylogenetic trees were constructed and showed that more strains were present in SI than in SS. HgcA sequences in SS were confined to three evolutionarily distant clades, δ-Proteobacteria, a methanogen group, and a Clostridia group, which was relatively rare among most clades.
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Affiliation(s)
- Hongxia Du
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China
- Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing, 400715, China
| | - Ming Ma
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China
- Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400715, China
| | - Tao Sun
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China
- Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400715, China
| | - Xianzhu Dai
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China
- Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing, 400715, China
| | - Caiyun Yang
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China
- Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing, 400715, China
| | - Feng Luo
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China
- Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing, 400715, China
| | - Dingyong Wang
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China.
- Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400715, China.
| | - Yasuo Igarashi
- College of Resources and Environment, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing, 400715, People's Republic of China.
- Research Center of Bioenergy and Bioremediation, Southwest University, Chongqing, 400715, China.
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428
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Zhang D, Yin Y, Li Y, Cai Y, Liu J. Critical role of natural organic matter in photodegradation of methylmercury in water: Molecular weight and interactive effects with other environmental factors. THE SCIENCE OF THE TOTAL ENVIRONMENT 2017; 578:535-541. [PMID: 27839761 DOI: 10.1016/j.scitotenv.2016.10.222] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 10/29/2016] [Accepted: 10/30/2016] [Indexed: 06/06/2023]
Abstract
Photodegradation is the main depletion pathway of methylmercury (MeHg) in surface water. However, the underlying mechanism of MeHg photodegradation is still not well understood. In this study, the critical role of natural organic matter (NOM) from Suwannee River natural organic matter of the International Humic Substance Society, especially its molecular weight, and the impacts of other related environmental factors in MeHg photodegradation were investigated. We observed that MeHg cannot photo-degrade in de-ionized water, excluding the direct photodegradation of MeHg. While either NOM or Fe3+ alone induced MeHg photodegradation, co-existing NOM significantly inhibited the Fe3+-induced degradation, highlighting the critical and complex role of NOM in MeHg photodegradation. Additionally, MeHg exhibited different photodegradation rates in the presence of molecular weight fractionated natural organic matter (Mf-NOM). More importantly, high concentration of NOM caused light attenuation significantly inhibited the photodegradation of MeHg, which was more significant for high molecular weight Mf-NOM. In the presence of Mf-NOM, MeHg photodegradation was also affected by light quality, pH and co-existing Cl- and NO3-. The study is helpful for a better understanding of the critical role of NOM and other environmental factors on MeHg photodegradation in surface water.
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Affiliation(s)
- Dan Zhang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yongguang Yin
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Yanbin Li
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
| | - Yong Cai
- Institute of Environment and Health, Jianghan University, Wuhan 430056, China
| | - Jingfu Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
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429
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Draft Genome Sequence of Desulfovibrio BerOc1, a Mercury-Methylating Strain. GENOME ANNOUNCEMENTS 2017; 5:5/3/e01483-16. [PMID: 28104657 PMCID: PMC5255934 DOI: 10.1128/genomea.01483-16] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Desulfovibrio BerOc1 is a sulfate-reducing bacterium isolated from the Berre lagoon (French Mediterranean coast). BerOc1 is able to methylate and demethylate mercury. The genome size is 4,081,579 bp assembled into five contigs. We identified the hgcA and hgcB genes involved in mercury methylation, but not those responsible for mercury demethylation.
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430
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Jonsson S, Andersson A, Nilsson MB, Skyllberg U, Lundberg E, Schaefer JK, Åkerblom S, Björn E. Terrestrial discharges mediate trophic shifts and enhance methylmercury accumulation in estuarine biota. SCIENCE ADVANCES 2017; 3:e1601239. [PMID: 28138547 PMCID: PMC5271591 DOI: 10.1126/sciadv.1601239] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 11/27/2016] [Indexed: 05/03/2023]
Abstract
The input of mercury (Hg) to ecosystems is estimated to have increased two- to fivefold during the industrial era, and Hg accumulates in aquatic biota as neurotoxic methylmercury (MeHg). Escalating anthropogenic land use and climate change are expected to alter the input rates of terrestrial natural organic matter (NOM) and nutrients to aquatic ecosystems. For example, climate change has been projected to induce 10 to 50% runoff increases for large coastal regions globally. A major knowledge gap is the potential effects on MeHg exposure to biota following these ecosystem changes. We monitored the fate of five enriched Hg isotope tracers added to mesocosm scale estuarine model ecosystems subjected to varying loading rates of nutrients and terrestrial NOM. We demonstrate that increased terrestrial NOM input to the pelagic zone can enhance the MeHg bioaccumulation factor in zooplankton by a factor of 2 to 7 by inducing a shift in the pelagic food web from autotrophic to heterotrophic. The terrestrial NOM input also enhanced the retention of MeHg in the water column by up to a factor of 2, resulting in further increased MeHg exposure to pelagic biota. Using mercury mass balance calculations, we predict that MeHg concentration in zooplankton can increase by a factor of 3 to 6 in coastal areas following scenarios with 15 to 30% increased terrestrial runoff. The results demonstrate the importance of incorporating the impact of climate-induced changes in food web structure on MeHg bioaccumulation in future biogeochemical cycling models and risk assessments of Hg.
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Affiliation(s)
- Sofi Jonsson
- Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden
- Umeå Marine Sciences Centre, Umeå University, SE-910 20 Hörnefors, Sweden
| | - Agneta Andersson
- Umeå Marine Sciences Centre, Umeå University, SE-910 20 Hörnefors, Sweden
- Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
| | - Mats B. Nilsson
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
| | - Erik Lundberg
- Umeå Marine Sciences Centre, Umeå University, SE-910 20 Hörnefors, Sweden
| | - Jeffra K. Schaefer
- Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA
| | - Staffan Åkerblom
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden
- Corresponding author.
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431
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Majumder ELW, Wall JD. Uranium Bio-Transformations: Chemical or Biological Processes? ACTA ACUST UNITED AC 2017. [DOI: 10.4236/ojic.2017.72003] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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432
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Luo HW, Yin X, Jubb AM, Chen H, Lu X, Zhang W, Lin H, Yu HQ, Liang L, Sheng GP, Gu B. Photochemical reactions between mercury (Hg) and dissolved organic matter decrease Hg bioavailability and methylation. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017; 220:1359-1365. [PMID: 27836473 DOI: 10.1016/j.envpol.2016.10.099] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Revised: 10/04/2016] [Accepted: 10/31/2016] [Indexed: 06/06/2023]
Abstract
Atmospheric deposition of mercury (Hg) to surface water is one of the dominant sources of Hg in aquatic environments and ultimately drives methylmercury (MeHg) toxin accumulation in fish. It is known that freshly deposited Hg is more readily methylated by microorganisms than aged or preexisting Hg; however the underlying mechanism of this process is unclear. We report that Hg bioavailability is decreased by photochemical reactions between Hg and dissolved organic matter (DOM) in water. Photo-irradiation of Hg-DOM complexes results in loss of Sn(II)-reducible (i.e. reactive) Hg and up to an 80% decrease in MeHg production by the methylating bacterium Geobacter sulfurreducens PCA. Loss of reactive Hg proceeded at a faster rate with a decrease in the Hg to DOM ratio and is attributed to the possible formation of mercury sulfide (HgS). These results suggest a new pathway of abiotic photochemical formation of HgS in surface water and provide a mechanism whereby freshly deposited Hg is readily methylated but, over time, progressively becomes less available for microbial uptake and methylation.
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Affiliation(s)
- Hong-Wei Luo
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China
| | - Xiangping Yin
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Aaron M Jubb
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Hongmei Chen
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Weihua Zhang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, 510006, China
| | - Hui Lin
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Han-Qing Yu
- Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China
| | - Liyuan Liang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA
| | - Guo-Ping Sheng
- Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
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433
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Martín-Doimeadios RCR, Mateo R, Jiménez-Moreno M. Is gastrointestinal microbiota relevant for endogenous mercury methylation in terrestrial animals? ENVIRONMENTAL RESEARCH 2017; 152:454-461. [PMID: 27321709 DOI: 10.1016/j.envres.2016.06.018] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Revised: 06/03/2016] [Accepted: 06/09/2016] [Indexed: 06/06/2023]
Abstract
The active role of gastrointestinal microbiota in mercury (Hg) methylation has been investigated in different terrestrial organisms from insects or annelids to rats and mammals, including the human beings. Some findings reveal the animal digestive tracts as new potential niches for Hg methylation especially in terrestrial invertebrates. However, contradictory results have been reported so far and there is still a long way to fully understand how important the MeHg production in this habitat could be, as well as its implications on the toxicity and biomagnification of MeHg within terrestrial food chains. It is important to know what has been studied in the past and discuss the previous results according to the new perspectives opened in this field. Therefore, the aim of this work is to review the present state of knowledge about the potential capability of gastrointestinal microbiota in Hg methylation with special emphasis in terrestrial animals and to propose new approaches profiting the new and powerful molecular and analytical tools.
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Affiliation(s)
- R C Rodríguez Martín-Doimeadios
- Departamento de Química Analítica y Tecnología de Alimentos, Instituto de Ciencias Ambientales, Universidad de Castilla-La Mancha, 45071 Toledo, Spain.
| | - R Mateo
- Instituto de Recursos Cinegéticos IREC-CSIC-UCLM, 13071 Ciudad Real, Spain
| | - M Jiménez-Moreno
- Departamento de Química Analítica y Tecnología de Alimentos, Instituto de Ciencias Ambientales, Universidad de Castilla-La Mancha, 45071 Toledo, Spain
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434
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Liu YR, Lu X, Zhao L, An J, He JZ, Pierce EM, Johs A, Gu B. Effects of Cellular Sorption on Mercury Bioavailability and Methylmercury Production by Desulfovibrio desulfuricans ND132. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:13335-13341. [PMID: 27993064 DOI: 10.1021/acs.est.6b04041] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Microbial conversion of inorganic mercury (IHg) to methylmercury (MeHg) is a significant environmental concern because of the bioaccumulation and biomagnification of toxic MeHg in the food web. Laboratory incubation studies have shown that, despite the presence of large quantities of IHg in cell cultures, MeHg biosynthesis often reaches a plateau or a maximum within hours or a day by an as yet unexplained mechanism. Here we report that mercuric Hg(II) can be taken up rapidly by cells of Desulfovibrio desulfuricans ND132, but a large fraction of the Hg(II) is unavailable for methylation because of strong cellular sorption. Thiols, such as cysteine, glutathione, and penicillamine, added either simultaneously with Hg(II) or after cells have been exposed to Hg(II), effectively desorb or mobilize the bound Hg(II), leading to a substantial increase in MeHg production. The amount of thiol-desorbed Hg(II) is strongly correlated to the amount of MeHg produced (r = 0.98). However, cells do not preferentially take up Hg(II)-thiol complexes, but Hg(II)-ligand exchange between these complexes and the cell-associated proteins likely constrains Hg(II) uptake and methylation. We suggest that, aside from aqueous chemical speciation of Hg(II), binding and exchange of Hg(II) between cells and complexing ligands such as thiols and naturally dissolved organics in solution is an important controlling mechanism of Hg(II) bioavailability, which should be considered when predicting MeHg production in the environment.
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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 100085, China
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Linduo Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Jing An
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Ji-Zheng He
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, China
- Department of Veterinary and Agricultural Sciences, the University of Melbourne , Melbourne, Victoria 3010, Australia
| | - Eric M Pierce
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Alexander Johs
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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435
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Rothenberg SE, Anders M, Ajami NJ, Petrosino JF, Balogh E. Water management impacts rice methylmercury and the soil microbiome. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 572:608-617. [PMID: 27450246 PMCID: PMC5099098 DOI: 10.1016/j.scitotenv.2016.07.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 07/03/2016] [Accepted: 07/03/2016] [Indexed: 05/24/2023]
Abstract
Rice farmers are pressured to grow rice using less water. The impacts of water-saving rice cultivation methods on rice methylmercury concentrations are uncertain. Rice (Oryza sativa L. cv. Nipponbare) was cultivated in fields using four water management treatments, including flooded (no dry-downs), alternating wetting and drying (AWD) (with one or three dry-downs), and furrow-irrigated fields (nine dry-downs) (n=16 fields). Anoxic bulk soil was collected from rice roots during the rice maturation phase, and rice grain was harvested after fields were dried. Total mercury and methylmercury concentrations were determined in soil and polished rice samples, and the soil microbiome was analyzed using 16S (v4) rRNA gene profiling. Soil total mercury did not differ between fields. However, compared to continuously flooded fields, soil and rice methylmercury concentrations averaged 51% and 38% lower in the AWD fields, respectively, and 95% and 96% lower in the furrow-irrigated fields, respectively. Compared to flooded fields, grain yield was reduced on average by <1% in the AWD fields and 34% in the furrow-irrigated fields. Additionally, using 16S (v4) rRNA gene profiling, the relative abundance of genera (i.e., highest resolution via this method) known to contain mercury methylators averaged 2.9-fold higher in flooded and AWD fields compared to furrow-irrigated fields. These results reinforce the benefits of AWD in reducing rice methylmercury concentrations with minimal changes in rice production yields. In the furrow-irrigated fields, a lower relative abundance of genera known to contain mercury methylators suggests an association between lower concentrations of soil and rice methylmercury and specific soil microbiomes.
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Affiliation(s)
- Sarah E Rothenberg
- Department of Environmental Health Sciences, University of South Carolina, Columbia, SC, USA.
| | - Merle Anders
- Department of Crop, Soil and Environmental Sciences, University of Arkansas Rice Research & Extension Center, Stuttgart, AR, USA.
| | - Nadim J Ajami
- The Alkek Center for Metagenomics and Microbiome Research, Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA.
| | - Joseph F Petrosino
- The Alkek Center for Metagenomics and Microbiome Research, Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA.
| | - Erika Balogh
- Department of Biological Sciences, University of South Carolina, Columbia, SC, USA.
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436
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Mazrui NM, Jonsson S, Thota S, Zhao J, Mason RP. Enhanced availability of mercury bound to dissolved organic matter for methylation in marine sediments. GEOCHIMICA ET COSMOCHIMICA ACTA 2016; 194:153-162. [PMID: 28127088 PMCID: PMC5257343 DOI: 10.1016/j.gca.2016.08.019] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The forms of inorganic mercury (HgII) taken up and methylated by bacteria in sediments still remain largely unknown. From pure cultures studies, it has been suggested that dissolved organic matter (DOM) may facilitate the uptake either by acting as a shuttle molecule, transporting the HgII atom to divalent metal transporters, or by binding HgII and then being transported into the cell as a carbon source. Enhanced availability of Hg complexed to DOM has however not yet been demonstrated in natural systems. Here, we show that HgII complexed with DOM of marine origin was up to 2.7 times more available for methylation in sediments than HgII added as a dissolved inorganic complex (HgII(aq)). We argue that the DOM used to complex HgII directly facilitated the bacterial uptake of HgII whereas the inorganic dissolved HgII-complex adsorbed to the sediment matrix before forming bioavailable dissolved HgII complexes. We further demonstrate that differences in net methylation in sediments with high and low organic carbon content may be explained by differences in the availability of carbon to stimulate the activity of Hg methylating bacteria rather than, as previously proposed, be due to differences in HgII binding capacities between sediments.
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Affiliation(s)
- Nashaat M. Mazrui
- Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT 06340, USA
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA
| | - Sofi Jonsson
- Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT 06340, USA
- Center for Environment and Sustainability, University of Gothenburg, Box 170, SE-405 30,Gothenburg, Sweden
| | - Sravan Thota
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA
| | - Jing Zhao
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA
| | - Robert P. Mason
- Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT 06340, USA
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA
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437
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Mercury alters the bacterial community structure and diversity in soil even at concentrations lower than the guideline values. Appl Microbiol Biotechnol 2016; 101:2163-2175. [PMID: 27873000 DOI: 10.1007/s00253-016-7965-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 10/26/2016] [Accepted: 10/31/2016] [Indexed: 12/13/2022]
Abstract
This study evaluated the effect of inorganic mercury (Hg) on bacterial community and diversity in different soils. Three soils-neutral, alkaline and acidic-were spiked with six different concentrations of Hg ranging from 0 to 200 mg kg-1 and aged for 90 days. At the end of the ageing period, 18 samples from three different soils were investigated for bacterial community structure and soil physicochemical properties. Illumina MiSeq-based 16s ribosomal RNA (rRNA) amplicon sequencing revealed the alteration in the bacterial community between un-spiked control soils and Hg-spiked soils. Among the bacterial groups, Actinobacteria (22.65%) were the most abundant phyla in all samples followed by Proteobacteria (21.95%), Bacteroidetes (4.15%), Firmicutes (2.9%) and Acidobacteria (2.04%). However, the largest group showing increased abundance with higher Hg doses was the unclassified group (45.86%), followed by Proteobacteria. Mercury had a considerable negative impact on key soil functional bacteria such as ammonium oxidizers and nitrifiers. Canonical correspondence analysis (CCA) indicated that among the measured soil properties, Hg had a major influence on bacterial community structure. Furthermore, nonlinear regression analysis confirmed that Hg significantly decreased soil bacterial alpha diversity in lower organic carbon containing neutral and alkaline soils, whereas in acidic soil with higher organic carbon there was no significant correlation. EC20 values obtained by a nonlinear regression analysis indicated that Hg significantly decreased soil bacterial diversity in concentrations lower than several guideline values.
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438
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Schwartz GE, Redfern LK, Ikuma K, Gunsch CK, Ruhl LS, Vengosh A, Hsu-Kim H. Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2016; 18:1427-1439. [PMID: 27722355 DOI: 10.1039/c6em00458j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Mercury (Hg) associated with coal ash is an environmental concern, particularly if the release of coal ash to the environment is associated with the conversion of inorganic Hg to methylmercury (MeHg), a bioaccumulative form of Hg that is produced by anaerobic microorganisms. In this study, sediment slurry microcosm experiments were performed to understand how spilled coal ash might influence MeHg production in anaerobic sediments of an aquatic ecosystem. Two coal ash types were used: (1) a weathered coal ash; and (2) a freshly collected, unweathered fly ash that was relatively enriched in sulfate and Hg compared to the weathered ash. These ash samples were added to anaerobic sediment slurries constructed with a relatively pristine sediment (containing 0.03 mg kg-1 Hg) and a Hg-contaminated sediment (containing 0.29 mg kg-1 Hg). The results of these experiments showed negligible net production of MeHg in microcosms with no ash and in microcosms amended with the low sulfate/low Hg ash. In contrast, slurry microcosms amended with high sulfate/high Hg ash showed increases in total MeHg content that was 2 to 3 times greater than control microcosms without ash (p < 0.001). 16S amplicon sequencing of microbial communities in the slurries indicated that the coal ash addition generally increased the relative abundance of the methylating microbial community, including sulfate-reducing bacteria and iron-reducing bacteria species that are known to be efficient methylators of Hg. The stimulation of these microorganisms was likely caused by the release of substrates (sulfate and Fe) originating from the ash. Overall, the results highlight the need to incorporate both environmental parameters and coal ash characteristics into risk assessments that guide coal ash management and disposal.
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Affiliation(s)
- Grace E Schwartz
- Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA.
| | - Lauren K Redfern
- Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA.
| | - Kaoru Ikuma
- Iowa State University, Department of Civil, Construction, and Environmental Engineering, Ames, Iowa 50011, USA
| | - Claudia K Gunsch
- Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA.
| | - Laura S Ruhl
- University of Arkansas-Little Rock, Department of Earth Sciences, Little Rock, Arkansas 72204, USA
| | - Avner Vengosh
- Duke University, Division of Earth and Ocean Sciences, Nicholas School of the Environment, Durham, North Carolina, USA
| | - Heileen Hsu-Kim
- Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA.
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439
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Liu YR, Dong JX, Zhang QG, Wang JT, Han LL, Zeng J, He JZ. Longitudinal occurrence of methylmercury in terrestrial ecosystems of the Tibetan Plateau. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2016; 218:1342-1349. [PMID: 27613323 DOI: 10.1016/j.envpol.2016.08.093] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Revised: 08/31/2016] [Accepted: 08/31/2016] [Indexed: 06/06/2023]
Abstract
Methylmercury (MeHg), a neurotoxin, is a global concern because of its potential risk to human and ecological health. Elevated mercury (Hg) concentrations were recently reported in the Tibetan Plateau (TP) due to increasing Hg input from distant regions, yet little is known about MeHg production and distribution in the terrestrial ecosystems of the TP. Here, we report longitudinal occurrence of MeHg and the factors regulating net MeHg production in 23 grassland sites from eastern to western TP. The soil MeHg content varied from 0.002 to 0.058 ng g-1, with different distribution patterns between the eastern and western TP. There was a positive correlation between the MeHg concentration and the longitude after 90 °E, which is similar to the distribution patterns of the total mercury (THg), water and organic carbon in this region. Average MeHg concentration in topsoil is generally higher than that in subsoil. Our results show that MeHg concentration in soils of the TP is directly affected by soil water, potential microbial methylators and THg, while indirectly regulated by soil organic carbon through the microbial community and the longitude-dependent precipitation through soil water. Our study suggests that soil water is the most important driver regulating net MeHg production in the grasslands of the TP. These findings have important implications for unraveling the mechanism of net production of MeHg in high-altitude environments.
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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 100085, China.
| | - Ji-Xin Dong
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Qiang-Gong Zhang
- Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Jun-Tao Wang
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Li-Li Han
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Jun Zeng
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Ji-Zheng He
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville 3010, Victoria, Australia
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440
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Gascón Díez E, Loizeau JL, Cosio C, Bouchet S, Adatte T, Amouroux D, Bravo AG. Role of Settling Particles on Mercury Methylation in the Oxic Water Column of Freshwater Systems. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:11672-11679. [PMID: 27670225 DOI: 10.1021/acs.est.6b03260] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
As the methylation of inorganic mercury to neurotoxic methylmercury has been attributed to the activity of anaerobic bacteria, the formation of methylmercury in the oxic water column of marine ecosystems has puzzled scientists over the past years. Here we show for the first time that methylmercury can be produced in particles sinking through oxygenated water column of lakes. Total mercury and methylmercury concentrations were measured in the settling particles and in surface sediments of the largest freshwater lake in Western Europe (Lake Geneva). While total mercury concentration differences between sediments and settling particles were not significant, methylmercury concentrations were about ten-fold greater in settling particles. Methylmercury demethylation rate constants (kd) were of similar magnitude in both compartments. In contrast, mercury methylation rate constants (km) were one order of magnitude greater in settling particles. The net potential for methylmercury formation, assessed by the ratio between the two rate constants (km kd-1), was therefore up to ten fold greater in settling particles, denoting that in situ transformations likely contributed to the high methylmercury concentration found in settling particles. Mercury methylation was inhibited (∼80%) in settling particles amended with molybdate, demonstrating the prominent role of biological sulfate-reduction in the process.
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Affiliation(s)
- Elena Gascón Díez
- Department F.-A. Forel for Environmental and Water Sciences, University of Geneva , Boulevard Carl-Vogt 66, 1211 Geneva 4, Switzerland
| | - Jean-Luc Loizeau
- Department F.-A. Forel for Environmental and Water Sciences, University of Geneva , Boulevard Carl-Vogt 66, 1211 Geneva 4, Switzerland
| | - Claudia Cosio
- Department F.-A. Forel for Environmental and Water Sciences, University of Geneva , Boulevard Carl-Vogt 66, 1211 Geneva 4, Switzerland
| | - Sylvain Bouchet
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc , 64053 Pau, France
| | - Thierry Adatte
- Institute of Earth Sciences (ISTE), University of Lausanne , 1015 Lausanne, Switzerland
| | - David Amouroux
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc , 64053 Pau, France
| | - Andrea G Bravo
- Limnology Department, Evolutionary Biology Centre, EBC, Norbyvägen 18D, 75236 Uppsala, Sweden
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441
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Olsen TA, Brandt CC, Brooks SC. Periphyton Biofilms Influence Net Methylmercury Production in an Industrially Contaminated System. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:10843-10850. [PMID: 27617484 DOI: 10.1021/acs.est.6b01538] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Mercury (Hg) methylation and methylmercury (MMHg) demethylation activity of periphyton biofilms from the industrially contaminated East Fork Poplar Creek, Tennessee (EFPC) were measured during 2014-2016 using stable Hg isotopic rate assays. 201HgII and MM202Hg were added to intact periphyton samples in ambient streamwater and the formation of MM201Hg and loss of MM202Hg were monitored over time and used to calculate first-order rate potentials for methylation and demethylation. The influences of location, temperature/season, light exposure and biofilm structure on methylation and demethylation potentials were examined. Between-site differences in net methylation for samples collected from an upstream versus downstream location were driven by differences in the demethylation rate potential (kd). In contrast, the within-site temperature-dependent difference in net methylation was driven by changes in the methylation rate potential (km). Samples incubated in the dark had lower net methylation due to lower km values than those incubated in the light. Disrupting the biofilm structure decreased km and resulted in lower net methylation. Overall, the measured rates resulted in a net excess of MMHg generated which could account for 3.71-7.88 mg d-1 MMHg flux in EFPC and suggests intact, actively photosynthesizing periphyton biofilms harbor zones of MMHg production.
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Affiliation(s)
- Todd A Olsen
- Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008 MS 6038, Oak Ridge, Tennessee 37831-6038, United States
| | - Craig C Brandt
- Biosciences Division, Oak Ridge National Laboratory, P.O. Box 2008 MS 6038, Oak Ridge, Tennessee 37831-6038, United States
| | - Scott C Brooks
- Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008 MS 6038, Oak Ridge, Tennessee 37831-6038, United States
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442
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Ndungu K, Schaanning M, Braaten HFV. Effects of organic matter addition on methylmercury formation in capped and uncapped marine sediments. WATER RESEARCH 2016; 103:401-407. [PMID: 27494695 DOI: 10.1016/j.watres.2016.07.055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 06/09/2016] [Accepted: 07/22/2016] [Indexed: 06/06/2023]
Abstract
In situ subaqueous capping (ISC) of contaminated marine sediments is frequently proposed as a feasible and effective mitigation option. However, though effective in isolating mercury species migration into overlying water, capping can also alter the location and extent of biogeochemical zones and potentially enhance methylmercury (MeHg) formation in Hg-contaminated marine sediments. We carried out a boxcosm study to investigate whether the addition of organic carbon (OC) to Hg-contaminated marine sediments beneath an in situ cap would initiate and/or enhance MeHg formation of the inorganic Hg present. The study was motivated by ongoing efforts to remediate ca. 30,000 m(2) of Hg-contaminated seabed sediments from a Hg spill from the U864 WWII submarine wreck. By the time of sinking, the submarine is assumed to have been holding a cargo of ca. 65 tons of liquid Hg. Natural organic matter and petroleum hydrocarbons from fuels and lubricants in the wreck are potential sources of organic carbon that could potentially fuel MeHg formation beneath a future cap. The results of our study clearly demonstrated that introduction of algae OC to Hg-contaminated sediments, triggered high rates of MeHg production as long a there was sufficient OC. Thus, MeHg production was limited by the amount of organic carbon available. The study results also confirmed that, within the six-month duration of the study and in the absence of bioturbating fauna, a 3-cm sediment clay cap could effectively reduce fluxes of Hg species to the overlying water and isolate the Hg-contaminated sediments from direct surficial deposition of organic matter that could potentially fuel methylation.
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Affiliation(s)
- Kuria Ndungu
- Norwegian Institute for Water Research-NIVA, Gaustadalleen 21, 0349, Oslo, Norway.
| | - Morten Schaanning
- Norwegian Institute for Water Research-NIVA, Gaustadalleen 21, 0349, Oslo, Norway
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443
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Eagles-Smith CA, Wiener JG, Eckley CS, Willacker JJ, Evers DC, Marvin-DiPasquale M, Obrist D, Fleck JA, Aiken GR, Lepak JM, Jackson AK, Webster JP, Stewart AR, Davis JA, Alpers CN, Ackerman JT. Mercury in western North America: A synthesis of environmental contamination, fluxes, bioaccumulation, and risk to fish and wildlife. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 568:1213-1226. [PMID: 27320732 DOI: 10.1016/j.scitotenv.2016.05.094] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 05/12/2016] [Accepted: 05/13/2016] [Indexed: 05/25/2023]
Abstract
Western North America is a region defined by extreme gradients in geomorphology and climate, which support a diverse array of ecological communities and natural resources. The region also has extreme gradients in mercury (Hg) contamination due to a broad distribution of inorganic Hg sources. These diverse Hg sources and a varied landscape create a unique and complex mosaic of ecological risk from Hg impairment associated with differential methylmercury (MeHg) production and bioaccumulation. Understanding the landscape-scale variation in the magnitude and relative importance of processes associated with Hg transport, methylation, and MeHg bioaccumulation requires a multidisciplinary synthesis that transcends small-scale variability. The Western North America Mercury Synthesis compiled, analyzed, and interpreted spatial and temporal patterns and drivers of Hg and MeHg in air, soil, vegetation, sediments, fish, and wildlife across western North America. This collaboration evaluated the potential risk from Hg to fish, and wildlife health, human exposure, and examined resource management activities that influenced the risk of Hg contamination. This paper integrates the key information presented across the individual papers that comprise the synthesis. The compiled information indicates that Hg contamination is widespread, but heterogeneous, across western North America. The storage and transport of inorganic Hg across landscape gradients are largely regulated by climate and land-cover factors such as plant productivity and precipitation. Importantly, there was a striking lack of concordance between pools and sources of inorganic Hg, and MeHg in aquatic food webs. Additionally, water management had a widespread influence on MeHg bioaccumulation in aquatic ecosystems, whereas mining impacts where relatively localized. These results highlight the decoupling of inorganic Hg sources with MeHg production and bioaccumulation. Together the findings indicate that developing efforts to control MeHg production in the West may be particularly beneficial for reducing food web exposure instead of efforts to simply control inorganic Hg sources.
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Affiliation(s)
- Collin A Eagles-Smith
- U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331, USA.
| | - James G Wiener
- University of Wisconsin La Crosse, River Studies Center, 1725 State Street, La Crosse, WI 54601, USA
| | - Chris S Eckley
- U.S. Environmental Protection Agency, Region-10, 2100 6th Ave., Suite 900, Seattle, WA 98101, USA
| | - James J Willacker
- U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331, USA
| | - David C Evers
- Biodiversity Research Institute, 276 Canco Road, Portland, ME 04103, USA
| | | | - Daniel Obrist
- Desert Research Institute, Division of Atmospheric Sciences, 2215 Raggio Parkway, Reno, NV 89512, USA
| | - Jacob A Fleck
- U.S. Geological Survey, California Water Science Center, 6000 J St., Placer Hall, Sacramento, CA 95819, USA
| | - George R Aiken
- U.S. Geological Survey, National Research Program, 3215 Marine St., Boulder, CO 80303, USA
| | - Jesse M Lepak
- Colorado Parks and Wildlife, 317 West Prospect Road, Fort Collins, CO 80526, USA
| | - Allyson K Jackson
- Oregon State University, Department of Fisheries and Wildlife, 104 Nash Hall, Corvallis, OR 97331, USA
| | - Jackson P Webster
- University of Colorado, Civil, Environmental, and Architectural Engineering, Boulder, CO 80309, USA
| | - A Robin Stewart
- U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA
| | - Jay A Davis
- San Francisco Estuary Institute, 4911 Central Ave., Richmond, CA 94804, USA
| | - Charles N Alpers
- U.S. Geological Survey, California Water Science Center, 6000 J St., Placer Hall, Sacramento, CA 95819, USA
| | - Joshua T Ackerman
- U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Dixon, CA 95620, USA
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444
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Økelsrud A, Lydersen E, Fjeld E. Biomagnification of mercury and selenium in two lakes in southern Norway. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 566-567:596-607. [PMID: 27236625 DOI: 10.1016/j.scitotenv.2016.05.109] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Revised: 04/28/2016] [Accepted: 05/16/2016] [Indexed: 06/05/2023]
Abstract
We have investigated bioaccumulation and trophic transfer of both mercury (Hg) and selenium (Se) in two lakes in southern Norway to reveal a suggested mitigating effect of Se on Hg biota accumulation. The study included analysis of total Se (Se), total Hg (Hg), and methyl-mercury (MeHg) in water, littoral and pelagic invertebrates and perch (Perca fluviatilis), together with stable isotope analysis (δ(15)N and δ(13)C) in biota. Mean dissolved Se ranged from 22 to 59ngL(-1), while Hg and MeHg in lake water ranged from 1 to 3ngL(-1) and 0.01 to 0.06ngL(-1). Biota Se and Hg concentrations (dry weight) ranged from 0.41mgSekg(-1) and 0.06mgHgkg(-1) in primary littoral invertebrates and up to 2.9mg Sekg(-1) and 3.6mgHgkg(-1) in perch. Both Hg and Se biomagnified in the food web, with a trophic magnification factor (TMF) of 4.64 for Hg and 1.29 for Se. The reported positive transfer of Se in the food web, despite the low measured dissolved Se, suggest that a major proportion of the Se in these lakes are both highly bioavailable and bioaccumulative. However, we did not find support for a Se-facilitated inhibition in the accumulation of Hg in perch, as Se and Hg concentrations in perch muscle correlated positively and Se did not explain any variations in Hg after we controlled for the effects of other important covariates. We postulate that this may be a result of insufficient concentrations of dissolved Se and subsequently in biota in our studied lakes for an efficient Hg sequestration up the food web.
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Affiliation(s)
- Asle Økelsrud
- Department of Environmental and Health Studies, University College of Southeast Norway, Hallvard Eikas Plass 1, 3800 Bø, Norway.
| | - Espen Lydersen
- Department of Environmental and Health Studies, University College of Southeast Norway, Hallvard Eikas Plass 1, 3800 Bø, Norway
| | - Eirik Fjeld
- Norwegian Institute for Water Research, Gaustadalléen 21, 0349 Oslo, Norway
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445
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446
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Development and Validation of Broad-Range Qualitative and Clade-Specific Quantitative Molecular Probes for Assessing Mercury Methylation in the Environment. Appl Environ Microbiol 2016; 82:6068-78. [PMID: 27422835 PMCID: PMC5038027 DOI: 10.1128/aem.01271-16] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 07/08/2016] [Indexed: 01/07/2023] Open
Abstract
Two genes, hgcA and hgcB, are essential for microbial mercury (Hg) methylation. Detection and estimation of their abundance, in conjunction with Hg concentration, bioavailability, and biogeochemistry, are critical in determining potential hot spots of methylmercury (MeHg) generation in at-risk environments. We developed broad-range degenerate PCR primers spanning known hgcAB genes to determine the presence of both genes in diverse environments. These primers were tested against an extensive set of pure cultures with published genomes, including 13 Deltaproteobacteria, nine Firmicutes, and nine methanogenic Archaea genomes. A distinct PCR product at the expected size was confirmed for all hgcAB+ strains tested via Sanger sequencing. Additionally, we developed clade-specific degenerate quantitative PCR (qPCR) primers that targeted hgcA for each of the three dominant Hg-methylating clades. The clade-specific qPCR primers amplified hgcA from 64%, 88%, and 86% of tested pure cultures of Deltaproteobacteria, Firmicutes, and Archaea, respectively, and were highly specific for each clade. Amplification efficiencies and detection limits were quantified for each organism. Primer sensitivity varied among species based on sequence conservation. Finally, to begin to evaluate the utility of our primer sets in nature, we tested hgcA and hgcAB recovery from pure cultures spiked into sand and soil. These novel quantitative molecular tools designed in this study will allow for more accurate identification and quantification of the individual Hg-methylating groups of microorganisms in the environment. The resulting data will be essential in developing accurate and robust predictive models of Hg methylation potential, ideally integrating the geochemistry of Hg methylation to the microbiology and genetics of hgcAB. IMPORTANCE The neurotoxin methylmercury (MeHg) poses a serious risk to human health. MeHg production in nature is associated with anaerobic microorganisms. The recent discovery of the Hg-methylating gene pair, hgcA and hgcB, has allowed us to design and optimize molecular probes against these genes within the genomic DNA for microorganisms known to methylate Hg. The protocols designed in this study allow for both qualitative and quantitative assessments of pure-culture or environmental samples. With these protocols in hand, we can begin to study the distribution of Hg-methylating organisms in nature via a cultivation-independent strategy.
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447
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Kronberg RM, Jiskra M, Wiederhold JG, Björn E, Skyllberg U. Methyl Mercury Formation in Hillslope Soils of Boreal Forests: The Role of Forest Harvest and Anaerobic Microbes. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:9177-9186. [PMID: 27461938 DOI: 10.1021/acs.est.6b00762] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Final harvest (clear-cutting) of coniferous boreal forests has been shown to increase streamwater concentrations and export of the neurotoxin methyl mercury (MeHg) to freshwater ecosystems. Here, the spatial distribution of inorganic Hg and MeHg in soil as a consequence of clear-cutting is reported. A comparison of soils at similar positions along hillslopes in four 80 years old Norway spruce (Picea abies) stands (REFs) with those in four similar stands subjected to clear-cutting (CCs) revealed significantly (p < 0.05) enhanced MeHg concentrations (ng g(-1)), MeHg areal masses (g ha(-1)), and percent MeHg of HgTOT in O horizons of CCs located between 1 and 41 m from streams. Inorganic Hg measures did not differ between REFs and CCs at any position. The O horizon thickness did not differ between CCs and REFs, but the groundwater table and soil water content were significantly higher at CCs than at REFs. The largest difference in percent MeHg of HgTOT (12 times higher at CCs compared to REFs, p = 0.003) was observed in concert with a significant enhancement in soil water content (p = 0.0003) at intermediate hillslope positions (20-38 m from stream), outside the stream riparian zone. Incubation experiments demonstrated that soils having significantly enhanced soil pools of MeHg after clear-cutting also showed significantly enhanced methylation potential as compared with similarly positioned soils in mature reference stands. The addition of inhibitors demonstrated that sulfate-reducing bacteria (SRB) and methanogens were key methylators. Rates of demethylation did not differ between CCs and REFs. Our results suggest that enhanced water saturation of organic soils providing readily available electron donors stimulate Hg-methylating microbes to net formation and buildup of MeHg in O horizons after forest harvest.
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Affiliation(s)
- Rose-Marie Kronberg
- Department of Forest Ecology and Management, Swedish University Of Agricultural Sciences , SE-901 83 Umeå, Sweden
| | | | | | - Erik Björn
- Department of Chemistry, Umeå University , SE-901 87 Umeå, Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management, Swedish University Of Agricultural Sciences , SE-901 83 Umeå, Sweden
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448
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Qian C, Johs A, Chen H, Mann BF, Lu X, Abraham PE, Hettich RL, Gu B. Global Proteome Response to Deletion of Genes Related to Mercury Methylation and Dissimilatory Metal Reduction Reveals Changes in Respiratory Metabolism in Geobacter sulfurreducens PCA. J Proteome Res 2016; 15:3540-3549. [PMID: 27463218 DOI: 10.1021/acs.jproteome.6b00263] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Geobacter sulfurreducens PCA can reduce, sorb, and methylate mercury (Hg); however, the underlying biochemical mechanisms of these processes and interdependent metabolic pathways remain unknown. In this study, shotgun proteomics was used to compare global proteome profiles between wild-type G. sulfurreducens PCA and two mutant strains: a ΔhgcAB mutant, which is deficient in two genes known to be essential for Hg methylation and a ΔomcBESTZ mutant, which is deficient in five outer membrane c-type cytochromes and thus impaired in its ability for dissimilatory metal ion reduction. We were able to delineate the global response of G. sulfurreducens PCA in both mutants and identify cellular networks and metabolic pathways that were affected by the loss of these genes. Deletion of hgcAB increased the relative abundances of proteins implicated in extracellular electron transfer, including most of the c-type cytochromes, PilA-C, and OmpB, and is consistent with a previously observed increase in Hg reduction in the ΔhgcAB mutant. Deletion of omcBESTZ was found to significantly increase relative abundances of various methyltransferases, suggesting that a loss of dissimilatory reduction capacity results in elevated activity among one-carbon (C1) metabolic pathways and thus increased methylation. We show that G. sulfurreducens PCA encodes only the folate branch of the acetyl-CoA pathway, and proteins associated with the folate branch were found at lower abundance in the ΔhgcAB mutant strain than the wild type. This observation supports the hypothesis that the function of HgcA and HgcB is linked to C1 metabolism through the folate branch of the acetyl-CoA pathway by providing methyl groups required for Hg methylation.
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Affiliation(s)
- Chen Qian
- Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.,Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Alexander Johs
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Hongmei Chen
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Benjamin F Mann
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Paul E Abraham
- Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Robert L Hettich
- Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.,Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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449
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Janssen SE, Schaefer JK, Barkay T, Reinfelder JR. Fractionation of Mercury Stable Isotopes during Microbial Methylmercury Production by Iron- and Sulfate-Reducing Bacteria. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:8077-83. [PMID: 27392249 DOI: 10.1021/acs.est.6b00854] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The biological production of monomethylmercury (MeHg) in soils and sediments is an important factor controlling mercury (Hg) accumulation in aquatic and terrestrial food webs. In this study we examined the fractionation of Hg stable isotopes during Hg methylation in nongrowing cultures of the anaerobic bacteria Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Both organisms showed mass-dependent, but no mass-independent fractionation of Hg stable isotopes during Hg methylation. Despite differences in methylation rates, the two bacteria had similar Hg fractionation factors (αr/p = 1.0009 and 1.0011, respectively). Unexpectedly, δ(202)Hg values of MeHg for both organisms were 0.4‰ higher than the value of initial inorganic Hg after about 35% of inorganic Hg had been methylated. These results indicate that a (202)Hg-enriched pool of inorganic Hg was preferentially utilized as a substrate for methylation by these organisms, but that multiple intra- and/or extracellular pools supplied inorganic Hg for biological methylation. Understanding the controls of the Hg stable isotopic composition of microbially produced MeHg is important to identifying bioavailable Hg in natural systems and the interpretation of Hg stable isotopes in aquatic food webs.
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Affiliation(s)
- Sarah E Janssen
- Department of Environmental Sciences, Rutgers University , 14 College Farm Road, New Brunswick, New Jersey 08901, United States
| | - Jeffra K Schaefer
- Department of Environmental Sciences, Rutgers University , 14 College Farm Road, New Brunswick, New Jersey 08901, United States
| | - Tamar Barkay
- Department of Biochemistry and Microbiology, Rutgers University , 76 Lipman Drive, New Brunswick, New Jersey 08901, United States
| | - John R Reinfelder
- Department of Environmental Sciences, Rutgers University , 14 College Farm Road, New Brunswick, New Jersey 08901, United States
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450
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Gionfriddo CM, Tate MT, Wick RR, Schultz MB, Zemla A, Thelen MP, Schofield R, Krabbenhoft DP, Holt KE, Moreau JW. Microbial mercury methylation in Antarctic sea ice. Nat Microbiol 2016; 1:16127. [PMID: 27670112 DOI: 10.1038/nmicrobiol.2016.127] [Citation(s) in RCA: 102] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Accepted: 06/29/2016] [Indexed: 11/09/2022]
Abstract
Atmospheric deposition of mercury onto sea ice and circumpolar sea water provides mercury for microbial methylation, and contributes to the bioaccumulation of the potent neurotoxin methylmercury in the marine food web. Little is known about the abiotic and biotic controls on microbial mercury methylation in polar marine systems. However, mercury methylation is known to occur alongside photochemical and microbial mercury reduction and subsequent volatilization. Here, we combine mercury speciation measurements of total and methylated mercury with metagenomic analysis of whole-community microbial DNA from Antarctic snow, brine, sea ice and sea water to elucidate potential microbially mediated mercury methylation and volatilization pathways in polar marine environments. Our results identify the marine microaerophilic bacterium Nitrospina as a potential mercury methylator within sea ice. Anaerobic bacteria known to methylate mercury were notably absent from sea-ice metagenomes. We propose that Antarctic sea ice can harbour a microbial source of methylmercury in the Southern Ocean.
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Affiliation(s)
- Caitlin M Gionfriddo
- School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Michael T Tate
- Wisconsin Water Science Center, US Geological Survey, Middleton, Wisconsin 53562, USA
| | - Ryan R Wick
- Centre for Systems Genomics, University of Melbourne, Victoria 3010, Australia.,Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Mark B Schultz
- Centre for Systems Genomics, University of Melbourne, Victoria 3010, Australia.,Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Adam Zemla
- Computation Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550 USA
| | - Michael P Thelen
- Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - Robyn Schofield
- School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia
| | - David P Krabbenhoft
- Wisconsin Water Science Center, US Geological Survey, Middleton, Wisconsin 53562, USA
| | - Kathryn E Holt
- Centre for Systems Genomics, University of Melbourne, Victoria 3010, Australia.,Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - John W Moreau
- School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia
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