Quantification of Mercury Bioavailability for Methylation Using Diffusive Gradient in Thin-Film Samplers

Ndu, Udonna; Christensen, Geoff A.; Rivera, Nelson; Gionfriddo, Caitlin M.; Deshusses, Marc A.; Elias, Dwayne A.; Hsu‐Kim, Heileen

doi:10.1021/acs.est.8b00647

Cited by 49 publications

(49 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Mesohaline tidal salt marsh sediments were collected from a Phragmites -dominated area of the Global Change Research Wetland on the Rhode River (Edgewater, MD, United States), where soil Hg concentrations averaged 0.17 ± 0.007 mg kg –1 Hg ( Mitchell and Gilmour, 2008 ). Sandy Creek sediments were collected from a freshwater retention pond (Durham, NC, United States) that receives legacy Hg, with sediments averaging 0.05 ± 0.006 mg kg –1 Hg ( Ndu et al, 2018 ). Rice paddy soils were collected during the rice growing season from Yanwuping in Guizhou province, China.…”

Section: Methodsmentioning

confidence: 99%

An Improved hgcAB Primer Set and Direct High-Throughput Sequencing Expand Hg-Methylator Diversity in Nature

et al. 2020

Self Cite

View full text Add to dashboard Cite

The gene pair hgcAB is essential for microbial mercury methylation. Our understanding of its abundance and diversity in nature is rapidly evolving. In this study we developed a new broad-range primer set for hgcAB , plus an expanded hgcAB reference library, and used these to characterize Hg-methylating communities from diverse environments. We applied this new Hg-methylator database to assign taxonomy to hgcA sequences from clone, amplicon, and metagenomic datasets. We evaluated potential biases introduced in primer design, sequence length, and classification, and suggest best practices for studying Hg-methylator diversity. Our study confirms the emerging picture of an expanded diversity of HgcAB-encoding microbes in many types of ecosystems, with abundant putative mercury methylators Nitrospirae and Chloroflexi in several new environments including salt marsh and peat soils. Other common microbes encoding HgcAB included Phycisphaerae , Aminicenantes , Spirochaetes , and Elusimicrobia. Combined with high-throughput amplicon specific sequencing, the new primer set also indentified novel hgcAB sequences similar to Lentisphaerae , Bacteroidetes , Atribacteria , and candidate phyla WOR-3 and KSB1 bacteria. Gene abundance data also corroborate the important role of two “classic” groups of methylators ( Deltaproteobacteria and Methanomicrobia ) in many environments, but generally show a scarcity of hgcAB + Firmicutes . The new primer set was developed to specifically target hgcAB sequences found in nature, reducing degeneracy and providing increased sensitivity while maintaining broad diversity capture. We evaluated mock communities to confirm primer improvements, including culture spikes to environmental samples with variable DNA extraction and PCR amplification efficiencies. For select sites, this new workflow was combined with direct high-throughput hgcAB sequencing. The hgcAB diversity generated by direct amplicon sequencing confirmed the potential for novel Hg-methylators previously identified using metagenomic screens. A new phylogenetic analysis using sequences from freshwater, saline, and terrestrial environments showed Deltaproteobacteria HgcA sequences generally clustered among themselves, while metagenome-resolved HgcA sequences in other phyla tended to cluster by environment, suggesting horizontal gene transfer into many clades. HgcA from marine metagenomes often formed distinct subtrees from those sequenced from freshwater ecosystems. Overall the majority of HgcA sequences branch from a cluster of HgcAB ...

show abstract

Section: Methodsmentioning

confidence: 99%

An Improved hgcAB Primer Set and Direct High-Throughput Sequencing Expand Hg-Methylator Diversity in Nature

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…One advantage of thiol‐based samplers is that they may mimic the dominant MeHg ligands in nature (Zhang et al ; Jeremiason et al ; Liem‐Nguyen et al ) and thus potentially provide a good predictor of the flux to aquatic organisms. As a result, site‐specific uptake by thiol‐based DGT samplers (commonly referred to as C DGT or DGT‐labile) has been used to predict Hg availability for methylation (Ndu et al ), de novo MeHg production (Clarisse et al ), MeHg photodegradation rates (Fernández‐Gómez et al ), and MeHg uptake by biota (Clarisse et al ; Liu et al ; Amirbahman et al ).…”

Section: Introductionmentioning

confidence: 99%

“…Although DGT samplers for Hg or MeHg were originally developed as a method to estimate freely or total dissolved concentrations in porewater (C pw ; Dočekalová and Diviš ; Clarisse and Hintelmann ; Hong et al ), many studies have recognized that DGT samplers instead access a kinetically labile portion of the total Hg or MeHg pool in sediments (Merritt and Amirbahman ; Clarisse et al ; Peijnenburg et al ; Ndu et al ). Thiol‐based DGT samplers have generally behaved as predicted by the general form of the DGT mass accumulation equation, with linear Hg and MeHg uptake through several days, although deviations may occur during longer deployment periods (Gao et al ; Clarisse et al ; Amirbahman et al ) or as a result of the deposition of nanoparticles on sampler membranes (Pham et al ).…”

Section: Introductionmentioning

confidence: 99%

Development of a Novel Equilibrium Passive Sampling Device for Methylmercury in Sediment and Soil Porewaters

Sanders

McBurney

Gilmour

et al. 2020

Enviro Toxic and Chemistry

View full text Add to dashboard Cite

We explored the concept of equilibrium passive sampling for methylmercury (MeHg) using the strategy developed for hydrophobic organic chemicals. Passive sampling should allow prediction of the concentration of the chemically labile fraction of MeHg in sediment porewaters based on equilibrium partitioning into the sampler, without modeling diffusion rates through the sampler material. Our goals were to identify sampler materials with the potential to mimic MeHg partitioning into animals and sediments and provide reversible sorption in a time frame appropriate for in situ samplers. Candidate materials tested included a range of polymers embedded with suitable sorbents for MeHg. The most promising were activated carbon (AC) embedded in agarose, thiol-self-assembled monolayers on mesoporous supports embedded in agarose, and cysteine-functionalized polyethylene terephthalate, which yielded log sampler-water partition coefficients of 2.8 to 5 for MeHgOH and MeHg complexed with dissolved organic matter (Suwannee River humic acid). Sampler equilibration time in sediments was approximately 1 to 2 wk. Investigation of the MeHg accumulation mechanism by AC embedded in agarose suggested that sampling was kinetically influenced by MeHg interactions with AC particles and not limited by diffusion through the gel for this material. Also, AC exhibited relatively rapid desorption of Hg and MeHg, indicating that this sorbent is capable of reversible, equilibrium measurements. In sediment:water microcosms, porewater concentrations made with isotherm-calibrated passive samplers agreed within a factor of 2 (unamended sediment) or 4 (AC-amended sediment) with directly measured concentrations. The present study demonstrates a potential new approach to passive sampling of MeHg. Environ Toxicol Chem 2020;39:323-334.

show abstract

“…Chloride concentrations in Cub Bath were higher than those of typical freshwaters (0.82 mM), and in combination with low pH, could have decreased net Hg methylation rates without impacting the viability of methylating microorganisms (77). Other factors that may influence Hg bioavailability include dissolved organic material (DOM) and thiol-DOM interactions (79–81), and turbidity which likely limits photolytic Hg transformations.…”

Section: Discussionmentioning

confidence: 99%

Genome-resolved metagenomics and detailed geochemical speciation analyses yield new insights into microbial mercury cycling in geothermal springs

Gionfriddo

Stott

Power

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

ABSTRACTGeothermal systems emit substantial amounts of aqueous, gaseous and methylated mercury, but little is known about microbial influences on mercury speciation. Here we report results from genome-resolved metagenomics and mercury speciation analysis of acid warm springs in the Ngawha Geothermal Field (<55 °C, pH < 4.5), Northland Region, Aotearoa (New Zealand). Our aim was to identify the microorganisms genetically equipped for mercury methylation, demethylation, or Hg(II) reduction to volatile Hg(0) in these springs. Dissolved total and methylated mercury concentrations in two adjacent springs with different mercury speciation ranked among the highest reported from natural sources (250–16000 ng L−1 and 0.5–13.9 ng L−1, respectively). Total solid mercury concentrations in spring sediments ranged from 1273 to 7000 µg g−1. In the context of such ultra-high mercury levels, the geothermal microbiome was unexpectedly diverse, and dominated by acidophilic and mesophilic sulfur- and iron-cycling bacteria, mercury- and arsenic-resistant bacteria, and thermophilic and acidophilic archaea. Integrating microbiome structure and metagenomic potential with geochemical constraints, we constructed a conceptual model for biogeochemical mercury cycling in geothermal springs. The model includes abiotic and biotic controls on mercury speciation, and illustrates how geothermal mercury cycling may couple to microbial community dynamics and sulfur and iron biogeochemistry.IMPORTANCELittle is currently known about biogeochemical mercury cycling in geothermal systems. This manuscript presents an important new conceptual model, supported by genome-resolved metagenomic analysis and detailed geochemical measurements. This work provides a framework for studying natural geothermal mercury emissions globally. Specifically, our findings have implications for mercury speciation in wastewaters from geothermal power plants and the potential environmental impacts of microbially and abiotically formed mercury species, particularly where mobilized in spring waters that mix with surface- or ground-waters. Furthermore, in the context of thermophilic origins for microbial mercury volatilisation, this report yields new insights into how such processes may have evolved alongside microbial mercury methylation/demethylation, and the environmental constraints imposed by the geochemistry and mineralogy of geothermal systems.

show abstract

Quantification of Mercury Bioavailability for Methylation Using Diffusive Gradient in Thin-Film Samplers

Cited by 49 publications

References 54 publications

An Improved hgcAB Primer Set and Direct High-Throughput Sequencing Expand Hg-Methylator Diversity in Nature

An Improved hgcAB Primer Set and Direct High-Throughput Sequencing Expand Hg-Methylator Diversity in Nature

Development of a Novel Equilibrium Passive Sampling Device for Methylmercury in Sediment and Soil Porewaters

Genome-resolved metagenomics and detailed geochemical speciation analyses yield new insights into microbial mercury cycling in geothermal springs

Contact Info

Product

Resources

About