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Zhang L, Yin Y, Sun Y, Liang X, Graham DE, Pierce EM, Löffler FE, Gu B. Inhibition of Methylmercury and Methane Formation by Nitrous Oxide in Arctic Tundra Soil Microcosms. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:5655-5665. [PMID: 36976621 PMCID: PMC10100821 DOI: 10.1021/acs.est.2c09457] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 03/03/2023] [Accepted: 03/16/2023] [Indexed: 06/18/2023]
Abstract
Climate warming causes permafrost thaw predicted to increase toxic methylmercury (MeHg) and greenhouse gas [i.e., methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O)] formation. A microcosm incubation study with Arctic tundra soil over 145 days demonstrates that N2O at 0.1 and 1 mM markedly inhibited microbial MeHg formation, methanogenesis, and sulfate reduction, while it slightly promoted CO2 production. Microbial community analyses indicate that N2O decreased the relative abundances of methanogenic archaea and microbial clades implicated in sulfate reduction and MeHg formation. Following depletion of N2O, both MeHg formation and sulfate reduction rapidly resumed, whereas CH4 production remained low, suggesting that N2O affected susceptible microbial guilds differently. MeHg formation strongly coincided with sulfate reduction, supporting prior reports linking sulfate-reducing bacteria to MeHg formation in the Arctic soil. This research highlights complex biogeochemical interactions in governing MeHg and CH4 formation and lays the foundation for future mechanistic studies for improved predictive understanding of MeHg and greenhouse gas fluxes from thawing permafrost ecosystems.
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Affiliation(s)
- Lijie Zhang
- Environmental
Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- Department
of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Yongchao Yin
- Biosciences
Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- Center
for Environmental Biotechnology, University
of Tennessee, Knoxville, Tennessee 37996, United States
- Department
of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Yanchen Sun
- Center
for Environmental Biotechnology, University
of Tennessee, Knoxville, Tennessee 37996, United States
- Department
of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Xujun Liang
- Environmental
Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - David E. Graham
- 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
| | - Frank E. Löffler
- Biosciences
Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- Center
for Environmental Biotechnology, University
of Tennessee, Knoxville, Tennessee 37996, United States
- Department
of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, United States
- Department
of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
- Department
of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Baohua Gu
- Environmental
Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- Department
of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, Tennessee 37996, United States
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2
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Yunda E, Gutensohn M, Ramstedt M, Björn E. Methylmercury formation in biofilms of Geobacter sulfurreducens. Front Microbiol 2023; 14:1079000. [PMID: 36712188 PMCID: PMC9880215 DOI: 10.3389/fmicb.2023.1079000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 01/02/2023] [Indexed: 01/15/2023] Open
Abstract
Introduction Mercury (Hg) is a major environmental pollutant that accumulates in biota predominantly in the form of methylmercury (MeHg). Surface-associated microbial communities (biofilms) represent an important source of MeHg in natural aquatic systems. In this work, we report MeHg formation in biofilms of the iron-reducing bacterium Geobacter sulfurreducens. Methods Biofilms were prepared in media with varied nutrient load for 3, 5, or 7 days, and their structural properties were characterized using confocal laser scanning microscopy, cryo-scanning electron microscopy and Fourier-transform infrared spectroscopy. Results Biofilms cultivated for 3 days with vitamins in the medium had the highest surface coverage, and they also contained abundant extracellular matrix. Using 3 and 7-days-old biofilms, we demonstrate that G. sulfurreducens biofilms prepared in media with various nutrient load produce MeHg, of which a significant portion is released to the surrounding medium. The Hg methylation rate constant determined in 6-h assays in a low-nutrient assay medium with 3-days-old biofilms was 3.9 ± 2.0 ∙ 10-14 L ∙ cell-1 ∙ h-1, which is three to five times lower than the rates found in assays with planktonic cultures of G. sulfurreducens in this and previous studies. The fraction of MeHg of total Hg within the biofilms was, however, remarkably high (close to 50%), and medium/biofilm partitioning of inorganic Hg (Hg(II)) indicated low accumulation of Hg(II) in biofilms. Discussion These findings suggest a high Hg(II) methylation capacity of G. sulfurreducens biofilms and that Hg(II) transfer to the biofilm is the rate-limiting step for MeHg formation in this systems.
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Schwartz GE, Muller KA, Rathore SS, Wilpiszeski RL, Carrell AA, Cregger MA, Elias DA, Podar M, Painter SL, Brooks SC. Incorporating concentration-dependent sediment microbial activity into methylmercury production kinetics modeling. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2022; 24:1392-1405. [PMID: 34727150 DOI: 10.1039/d1em00287b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In anoxic environments, anaerobic microorganisms carrying the hgcAB gene cluster can mediate the transformation of inorganic mercury (Hg(II)) to monomethylmercury (MMHg). The kinetics of Hg(II) transformation to MMHg in periphyton from East Fork Poplar Creek (EFPC) in Oak Ridge, TN have previously been modeled using a transient availability model (TAM). The TAM for Hg(II) methylation combines methylation/demethylation kinetics with kinetic expressions for processes that decrease Hg(II) and MMHg availability for methylation and demethylation (multisite sorption of Hg(II) and MMHg, Hg(II) reduction/Hg(0) oxidation). In this study, the TAM is used for the first time to describe MMHg production in sediment. We assessed MMHg production in sediment microcosms using two different sediment types from EFPC: a relatively anoxic, carbon-rich sediment with higher microbial activity (higher CO2 production from sediment) and a relatively oxic, sandy, carbon-poor sediment with lower microbial activity (lower CO2 production from sediment). Based on 16s rRNA sequencing, the overall microbial community structure in the two sediments was retained during the incubations. However, the hgcA containing methanogenic Euryarchaeota communities differed between sediment types and their growth followed different trajectories over the course of incubations, potentially contributing to the distinct patterns of MMHg production observed. The general TAM paradigm performed well in describing MMHg production in the sediments. However, the MMHg production and ancillary data suggested the need to revise the model structure to incorporate terms for concentration-dependent microbial activity over the course of the incubations. We modified the TAM to include Monod-type kinetics for methylation and demethylation and observed an improved fit for the carbon-rich, microbially active sediment. Overall our work shows that the TAM can be applied to describe Hg(II) methylation in sediments and that including expressions accounting for concentration-dependent microbial activity can improve the accuracy of the model description of the data in some cases.
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Affiliation(s)
- Grace E Schwartz
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
| | - Katherine A Muller
- Earth Systems Science Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Saubhagya S Rathore
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
| | - Regina L Wilpiszeski
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Alyssa A Carrell
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Melissa A Cregger
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Dwayne A Elias
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Mircea Podar
- Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA
| | - Scott L Painter
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
| | - Scott C Brooks
- Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
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4
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Brooks SC, Riscassi AL, Miller CL, Lowe KA, Yin X, Mehlhorn TL. Diel mercury concentration variations in a mercury-impacted stream. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2022; 24:1195-1211. [PMID: 35829655 DOI: 10.1039/d2em00142j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Filtered and particulate mercury (Hg) and methylmercury (MMHg), and associated water chemistry parameters, were evaluated bi-hourly for several 30 h periods during the summer and winter seasons at several distinct locations (downstream forested, midstream urban/suburban, upstream industrial) along a creek contaminated with high levels of inorganic Hg to determine if biogeochemical Hg and MMHg cycles respond to the daily photocycle. In summer particulate Hg and MMHg concentrations doubled overnight (excluding the upstream industrial site) concurrent with increases in turbidity and total suspended sediment; no such pattern was evident in winter. Seasonal and diel changes in the activity of macrobiota affecting the suspension of contaminated sediments are likely responsible for these patterns as other potential explanatory variables (e.g., instrument drift, pH, discharge) could not account for the range and timing of our observations. Diel patterns in filtered Hg (HgD) were significant only at locations and times of the year when channel shading was not present and daytime concentrations increased 22-89% above nighttime minima likely caused by direct and indirect photochemical reactions. Relationships between HgD and dissolved organic carbon (DOC) concentration or character were inconsistent between sites. Unlike HgD, there were significant diel patterns in filtered MMHg (MMHgD) at all sites and times of year, with summer concentrations peaking in mid to late afternoon while the timing differed in winter, with concentrations peaking after sunset. Daily variability in MMHgD concentration ranged between 25 and 75%. The results imply key controls on net methylation occur within the stream or on the stream bed and include factors such as small-scale temperature changes in the water column and photosynthetic activity of stream biofilm. With respect to stream monitoring, results from this study indicate (1) consistent timing in stream Hg and MMHg sampling is required for accurate assessment of long-term trends, (2) in situ measurements of turbidity can be used to quantify diel dynamics of both particulate Hg and MMHg concentrations, and (3) in situ fluorescing dissolved organic matter (FDOM), a potential proxy for DOC, was not capable of resolving diel dynamics of filtered Hg or MMHg.
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Affiliation(s)
- Scott C Brooks
- Oak Ridge National Laboratory, Environmental Sciences Division, PO Box 2008, MS 6038, Oak Ridge, TN, 37831-6038, USA.
| | - Ami L Riscassi
- University of Virginia, Environmental Sciences Department, 291 McCormick Rd., Charlottesville, VA, USA
| | - Carrie L Miller
- Theoretical and Applied Science, Ramapo College of New Jersey, Mahwah, New Jersey, USA
| | - Kenneth A Lowe
- Oak Ridge National Laboratory, Environmental Sciences Division, PO Box 2008, MS 6038, Oak Ridge, TN, 37831-6038, USA.
| | - Xiangping Yin
- Oak Ridge National Laboratory, Environmental Sciences Division, PO Box 2008, MS 6038, Oak Ridge, TN, 37831-6038, USA.
| | - Tonia L Mehlhorn
- Oak Ridge National Laboratory, Environmental Sciences Division, PO Box 2008, MS 6038, Oak Ridge, TN, 37831-6038, USA.
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5
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Yin X, Wang L, Liang X, Zhang L, Zhao J, Gu B. Contrary effects of phytoplankton Chlorella vulgaris and its exudates on mercury methylation by iron- and sulfate-reducing bacteria. JOURNAL OF HAZARDOUS MATERIALS 2022; 433:128835. [PMID: 35398798 DOI: 10.1016/j.jhazmat.2022.128835] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2022] [Revised: 03/29/2022] [Accepted: 03/30/2022] [Indexed: 06/14/2023]
Abstract
Mercury (Hg) is a pervasive environmental pollutant and poses serious health concerns as inorganic Hg(II) can be converted to the neurotoxin methylmercury (MeHg), which bioaccumulates and biomagnifies in food webs. Phytoplankton, representing the base of aquatic food webs, can take up Hg(II) and influence MeHg production, but currently little is known about how and to what extent phytoplankton may impact Hg(II) methylation by itself or by methylating bacteria it harbors. This study investigated whether some species of phytoplankton could produce MeHg and how the live or dead phytoplankton cells and excreted algal organic matter (AOM) impact Hg(II) methylation by several known methylators, including iron-reducing bacteria (FeRB), Geobacter anodireducens SD-1 and Geobacter sulfurreducens PCA, and the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans ND132 (or Pseudodesulfovibrio mercurii). Our results indicate that, among the 4 phytoplankton species studied, none were capable of methylating Hg(II). However, the presence of phytoplankton cells (either live or dead) from Chlorella vulgaris (CV) generally inhibited Hg(II) methylation by FeRB but substantially enhanced methylation by SRB D. desulfuricans ND132. Enhanced methylation was attributed in part to CV-excreted AOM, which increased Hg(II) complexation and methylation by ND132 cells. In contrast, inhibition of methylation by FeRB was attributed to these bacteria incapable of competing with phytoplankton for Hg(II) binding and uptake. These observations suggest that phytoplankton could play different roles in affecting Hg(II) methylation by the two groups of anaerobic bacteria, FeRB and SRB, and thus shed additional light on how phytoplankton blooms may modulate MeHg production and bioaccumulation in the aquatic environment.
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Affiliation(s)
- Xixiang Yin
- Shandong Jinan Eco-environmental Monitoring Center, Jinan 250014, China; Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Ten 37831, United States
| | - Lihong Wang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Ten 37831, United States; Qilu University of Technology (Shandong Academy of Sciences), Shandong Analysis and Test Center, Jinan 250014, China
| | - Xujun Liang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Ten 37831, United States
| | - Lijie Zhang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Ten 37831, United States
| | - Jiating Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Ten 37831, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Ten 37831, United States; Department of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, Ten 37996, United States.
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Liang X, Zhu N, Johs A, Chen H, Pelletier DA, Zhang L, Yin X, Gao Y, Zhao J, Gu B. Mercury Reduction, Uptake, and Species Transformation by Freshwater Alga Chlorella vulgaris under Sunlit and Dark Conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:4961-4969. [PMID: 35389633 DOI: 10.1021/acs.est.1c06558] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
As a major entry point of mercury (Hg) to aquatic food webs, algae play an important role in taking up and transforming Hg species in aquatic ecosystems. However, little is known how and to what extent Hg reduction, uptake, and species transformations are mediated by algal cells and their exudates, algal organic matter (AOM), under either sunlit or dark conditions. Here, using Chlorella vulgaris (CV) as one of the most prevalent freshwater model algal species, we show that solar irradiation could enhance the reduction of mercuric Hg(II) to elemental Hg(0) by both CV cells and AOM. AOM reduced more Hg(II) than algal cells themselves due to cell surface adsorption and uptake of Hg(II) inside the cells under solar irradiation. Synchrotron radiation X-ray absorption near-edge spectroscopy (SR-XANES) analyses indicate that sunlight facilitated the transformation of Hg to less bioavailable species, such as β-HgS and Hg-phytochelatins, compared to Hg(Cysteine)2-like species formed in algal cells in the dark. These findings highlight important functional roles and potential mechanisms of algae in Hg reduction and immobilization under varying lighting conditions and how these processes may modulate Hg cycling and bioavailability in the aquatic environment.
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Affiliation(s)
- Xujun Liang
- CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- School of Resources and Environment Science, Quanzhou Normal University, Quanzhou 362000, China
| | - Nali Zhu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China
| | - 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
| | - Dale A Pelletier
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Lijie Zhang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Xixiang Yin
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Yuxi Gao
- CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Jiating Zhao
- CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- 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
- Department of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, Tennessee 37996, United States
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7
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Zhang L, Philben M, Taş N, Johs A, Yang Z, Wullschleger SD, Graham DE, Pierce EM, Gu B. Unravelling biogeochemical drivers of methylmercury production in an Arctic fen soil and a bog soil. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2022; 299:118878. [PMID: 35085651 DOI: 10.1016/j.envpol.2022.118878] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 01/19/2022] [Accepted: 01/20/2022] [Indexed: 06/14/2023]
Abstract
Arctic tundra soils store a globally significant amount of mercury (Hg), which could be transformed to the neurotoxic methylmercury (MeHg) upon warming and thus poses serious threats to the Arctic ecosystem. However, our knowledge of the biogeochemical drivers of MeHg production is limited in these soils. Using substrate addition (acetate and sulfate) and selective microbial inhibition approaches, we investigated the geochemical drivers and dominant microbial methylators in 60-day microcosm incubations with two tundra soils: a circumneutral fen soil and an acidic bog soil, collected near Nome, Alaska, United States. Results showed that increasing acetate concentration had negligible influences on MeHg production in both soils. However, inhibition of sulfate-reducing bacteria (SRB) completely stalled MeHg production in the fen soil in the first 15 days, whereas addition of sulfate in the low-sulfate bog soil increased MeHg production by 5-fold, suggesting prominent roles of SRB in Hg(II) methylation. Without the addition of sulfate in the bog soil or when sulfate was depleted in the fen soil (after 15 days), both SRB and methanogens contributed to MeHg production. Analysis of microbial community composition confirmed the presence of several phyla known to harbor microorganisms associated with Hg(II) methylation in the soils. The observations suggest that SRB and methanogens were mainly responsible for Hg(II) methylation in these tundra soils, although their relative contributions depended on the availability of sulfate and possibly syntrophic metabolisms between SRB and methanogens.
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Affiliation(s)
- Lijie Zhang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA; Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, USA
| | - Michael Philben
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Neslihan Taş
- Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, USA
| | - Alexander Johs
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Ziming Yang
- Department of Chemistry, Oakland University, Rochester, MI, 48309, USA
| | - Stan D Wullschleger
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - David E Graham
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Eric M Pierce
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
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8
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Carrell AA, Schwartz GE, Cregger MA, Gionfriddo CM, Elias DA, Wilpiszeski RL, Klingeman DM, Wymore AM, Muller KA, Brooks SC. Nutrient Exposure Alters Microbial Composition, Structure, and Mercury Methylating Activity in Periphyton in a Contaminated Watershed. Front Microbiol 2021; 12:647861. [PMID: 33815336 PMCID: PMC8017159 DOI: 10.3389/fmicb.2021.647861] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 02/22/2021] [Indexed: 01/04/2023] Open
Abstract
The conversion of mercury (Hg) to monomethylmercury (MMHg) is a critical area of concern in global Hg cycling. Periphyton biofilms may harbor significant amounts of MMHg but little is known about the Hg-methylating potential of the periphyton microbiome. Therefore, we used high-throughput amplicon sequencing of the 16S rRNA gene, ITS2 region, and Hg methylation gene pair (hgcAB) to characterize the archaea/bacteria, fungi, and Hg-methylating microorganisms in periphyton communities grown in a contaminated watershed in East Tennessee (United States). Furthermore, we examined how nutrient amendments (nitrate and/or phosphate) altered periphyton community structure and function. We found that bacterial/archaeal richness in experimental conditions decreased in summer and increased in autumn relative to control treatments, while fungal diversity generally increased in summer and decreased in autumn relative to control treatments. Interestingly, the Hg-methylating communities were dominated by Proteobacteria followed by Candidatus Atribacteria across both seasons. Surprisingly, Hg methylation potential correlated with numerous bacterial families that do not contain hgcAB, suggesting that the overall microbiome structure of periphyton communities influences rates of Hg transformation within these microbial mats. To further explore these complex community interactions, we performed a microbial network analysis and found that the nitrate-amended treatment resulted in the highest number of hub taxa that also corresponded with enhanced Hg methylation potential. This work provides insight into community interactions within the periphyton microbiome that may contribute to Hg cycling and will inform future research that will focus on establishing mixed microbial consortia to uncover mechanisms driving shifts in Hg cycling within periphyton habitats.
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Affiliation(s)
- Alyssa A Carrell
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Grace E Schwartz
- Oak Ridge National Laboratory, Environmental Science Division, Oak Ridge, TN, United States.,Department of Chemistry, Wofford College, Spartanburg, SC, United States
| | - Melissa A Cregger
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Caitlin M Gionfriddo
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States.,Smithsonian Environmental Research Center, Edgewater, MD, United States
| | - Dwayne A Elias
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Regina L Wilpiszeski
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Dawn M Klingeman
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Ann M Wymore
- Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, United States
| | - Katherine A Muller
- Pacific Northwest National Laboratory, Earth Systems Science Division, Richland, WA, United States
| | - Scott C Brooks
- Oak Ridge National Laboratory, Environmental Science Division, Oak Ridge, TN, United States
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9
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Leclerc M, Harrison MC, Storck V, Planas D, Amyot M, Walsh DA. Microbial Diversity and Mercury Methylation Activity in Periphytic Biofilms at a Run-of-River Hydroelectric Dam and Constructed Wetlands. mSphere 2021; 6:e00021-21. [PMID: 33731467 PMCID: PMC8546676 DOI: 10.1128/msphere.00021-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 02/24/2021] [Indexed: 01/04/2023] Open
Abstract
Periphytic biofilms have the potential to greatly influence the microbial production of the neurotoxicant monomethylmercury in freshwaters although few studies have simultaneously assessed periphyton mercury methylation and demethylation rates and the microbial communities associated with these transformations. We performed a field study on periphyton from a river affected by run-of-river power plants and artificial wetlands in a boreal landscape (Québec, Canada). In situ incubations were performed on three sites using environmental concentrations of isotopically enriched monomethylmercury (MM198Hg) and inorganic mercury (200Hg) for demethylation and methylation rate measurements. Periphytic microbial communities were investigated through 16S rRNA gene analyses and metagenomic screenings for the hgcA gene, involved in mercury methylation. Positive mercury methylation rates ([5.9 ± 3.4] × 10-3 day-1) were observed only in the wetlands, and demethylation rates averaged 1.78 ± 0.21 day-1 for the three studied sites. The 16S rRNA gene analyses revealed Proteobacteria as the most abundant phylum across all sites (36.3% ± 1.4%), from which families associated with mercury methylation were mostly found in the wetland site. Metagenome screening for HgcA identified 24 different hgcA sequences in the constructed wetland site only, associated with 8 known families, where the iron-reducing Geobacteraceae were the most abundant. This work brings new information on mercury methylation in periphyton from habitats of impacted rivers, associating it mostly with putative iron-reducing bacteria.IMPORTANCE Monomethylmercury (MMHg) is a biomagnifiable neurotoxin of global concern with risks to human health mostly associated with fish consumption. Hydroelectric reservoirs are known to be sources of MMHg many years after their impoundment. Little is known, however, on run-of-river dams flooding smaller terrestrial areas, although their numbers are expected to increase considerably worldwide in decades to come. Production of MMHg is associated mostly with anaerobic processes, but Hg methylation has been shown to occur in periphytic biofilms located in oxic zones of the water column. Therefore, in this study, we investigated in situ production of MMHg by periphytic communities in habitats impacted by the construction of a run-of-river dam by combining transformation rate measurements with genomic approaches targeting hgcAB genes, responsible for mercury methylation. These results provide extended knowledge on mercury methylators in river ecosystems impacted by run-of-river dams in temperate habitats.
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Affiliation(s)
- Maxime Leclerc
- GRIL, Département de Sciences Biologiques, Université de Montréal, Montréal, Québec, Canada
- GRIL, Département de Sciences Biologiques, Université du Québec à Montréal, Montréal, Québec, Canada
| | | | - Veronika Storck
- GRIL, Département de Sciences Biologiques, Université de Montréal, Montréal, Québec, Canada
- Department of Biology, Concordia University, Montréal, Québec, Canada
| | - Dolors Planas
- GRIL, Département de Sciences Biologiques, Université du Québec à Montréal, Montréal, Québec, Canada
| | - Marc Amyot
- GRIL, Département de Sciences Biologiques, Université de Montréal, Montréal, Québec, Canada
| | - David A Walsh
- Department of Biology, Concordia University, Montréal, Québec, Canada
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Liem-Nguyen V, Skyllberg U, Björn E. Methylmercury formation in boreal wetlands in relation to chemical speciation of mercury(II) and concentration of low molecular mass thiols. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 755:142666. [PMID: 33059147 DOI: 10.1016/j.scitotenv.2020.142666] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 09/22/2020] [Accepted: 09/22/2020] [Indexed: 06/11/2023]
Abstract
Methylmercury (MeHg) is a neurotoxin formed from inorganic divalent mercury (HgII) via microbial methylation, and boreal wetlands have been identified as major sources of MeHg. There is however a lack of studies investigating the relationship between the chemical speciation of HgII and MeHg formation in such environments, in particular regarding to role of thiol compounds. We determined HgII methylation potentials, kmeth, in boreal wetland soils using two HgII isotope tracers: 198Hg(OH)2(aq) and HgII bonded to thiol groups in natural organic matter, 200HgII-NOM(ads), representing HgII sources with high and low availability for methylation. The 198Hg(OH)2(aq) tracer was consistently methylated to a 5-fold higher extent than 200HgII-NOM(ads), independent of environmental conditions. This suggests that the concentration of HgII in porewater was a decisive factor for HgII methylation. A comprehensive thermodynamic speciation model (including HgII complexes with inorganic sulfide (H2S), polysulfides (H2Sn), thiols associated with natural organic matter (NOM-RSH) and specific low molecular mass thiols (LMM-RSH) provided new insights on the speciation of HgII in boreal wetland porewaters, but did not demonstrate any clear relationship between kmeth and the calculated chemical speciation. In contrast, significant positive relationships were observed between kmeth and the sum of LMM thiol compounds of biological origin. We suggest two possible mechanisms underlying these correlations: 1) LMM thiols kinetically control the size and composition of the HgII pool available for microbial uptake, and/or 2) LMM thiols are produced by microbes such that the correlation reflects a relation between microbial activity and MeHg formation.
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Affiliation(s)
- Van Liem-Nguyen
- Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden; Laboratory of Advanced Materials Chemistry, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Viet Nam
| | - 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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