Global prevalence and distribution of genes and microorganisms involved in mercury methylation

Podar, Mircea; Gilmour, Cynthia C.; Brandt, Craig C.; Soren, Ally; Brown, Steven D.; Crable, Bryan R.; Palumbo, Anthony V.; Somenahally, Anil; Elias, Dwayne A.

doi:10.1126/sciadv.1500675

Cited by 379 publications

(482 citation statements)

References 69 publications

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“…Potential environments in which methylation may occur, as suggested by the environments of organisms with the hgcAB gene cluster, include invertebrate digestive tracts, thawing permafrost soils, coastal dead zones, and extreme environmental conditions (Podar et al 2015). In fact, studies using molecular techniques to directly examine potential sites of methylation are currently being published.…”

Section: Why Is Net Methylmercury Production Important and How It Ismentioning

confidence: 99%

“…Known methylators, including SRB and IRB, possess the genes responsible for methylation Parks et al 2013;Sonke et al 2013;Podar et al 2015). This gene pair has already enabled researchers to identify the methylating capacities of certain methanogens as well as Firmicutes (Parks et al 2013), particularly syntrophic, acetogenic, and fermentative varieties , several Proteobacteria, including five Deltaproteobacteria species , and Euryarchaeota of the archaea (Parks et al 2013) ( Table 2).…”

Section: Why Is Net Methylmercury Production Important and How It Ismentioning

confidence: 99%

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Recent advances in the study of mercury methylation in aquatic systems

Paranjape

Hall

2017

FACETS

121

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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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Section: Why Is Net Methylmercury Production Important and How It Ismentioning

confidence: 99%

Section: Why Is Net Methylmercury Production Important and How It Ismentioning

confidence: 99%

Recent advances in the study of mercury methylation in aquatic systems

Paranjape

Hall

2017

FACETS

121

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“…A wide variety of anaerobic microbes have been shown to produce MeHg (Gilmour et al, 2013;Podar et al, 2015;Parks et al, 2013), including Fe-reducing bacteria (FeRB) (Fleming et al, 2006;Kerin et al, 2006), sulfate-reducing bacteria (SRB) (Compeau and Bartha, 1985;Gilmour et al, 1992), methanogens (Hamelin et al, 2011), and syntrophs (Bae et al, 2014). The relative MeHg contribution of these groups can vary depending on the environment (Hamelin et al, 2011;Warner et al, 2003;Yu et al, 2012).…”

mentioning

confidence: 99%

“…Wetland soils, including rice fields, are important sites of MeHg production (Gilmour et al, 1998;Krabbenhoft et al, 1995;Marvin-DiPasquale et al, 2014;Podar et al, 2015;Windham-Myers et al, 2014). Methylmercury produced in rice field soil is accumulated by rice plants more readily than inorganic Hg (Strickman and Mitchell, 2017;Zhang et al, 2010).…”

mentioning

confidence: 99%

“…Methylmercuryis a toxic and highly bioaccumulative form of Hg (World Health Organization, 1990), and it is primarily produced by some groups of anaerobic microbes (Gilmour et al, 2013;Parks et al, 2013;Podar et al, 2015). Wetland soils, including rice fields, are important sites of MeHg production (Gilmour et al, 1998;Krabbenhoft et al, 1995;Marvin-DiPasquale et al, 2014;Podar et al, 2015;Windham-Myers et al, 2014).…”

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confidence: 99%

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Alternate Wetting and Drying Decreases Methylmercury in Flooded Rice (Oryza sativa) Systems

Tanner

Windham‐Myers

Marvin-DiPasquale

et al. 2018

Soil Science Soc of Amer J

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In flooded soils, including those found in rice (Oryza sativa L.) fields, microbes convert inorganic Hg to more toxic methylmercury (MeHg). Methylmercury is accumulated in rice grain, potentially affecting health. Methylmercury in rice field surface water can bioaccumulate in wildlife. We evaluated how introducing aerobic periods into an otherwise continuously flooded rice growing season affects MeHg dynamics. Conventional continuously flooded (CF) rice field water management was compared with alternate wetting and drying, where irrigation was stopped twice during the growing season, allowing soil to dry to 35% volumetric moisture content, at which point plots were reflooded ( Abbreviations: %Fe(II), ferrous iron as a percent of total citrate-dithionite extractable Fe; %MeHg, the percentage of total Hg that is methylmercury; AWD, alternate wetting and drying; AWD-35, alternate wetting and drying to 35% volumetric moisture content; CF, continuous flooding; DAP, day after planting; Fe(II) AE , acid-extractable ferrous Fe; (Fe(III) a, amorphous ferric iron; Fe T , total citrate-dithionite extractable Fe; FeRB, Fe-reducing bacteria; MeHg, methylmercury; SRB, sulfate-reducing bacteria; THg, total Mg. R ice is grown on 161 million ha worldwide and is the staple crop for 3.5 billion people globally (Muthayya et al., 2014). Rice is a semiaquatic plant and is usually grown under flooded conditions to help control weeds, increase nutrient availability, and ensure water supply during drought (Kendig et al., 2003). Flooded conditions also allow rice fields to serve as important wildlife habitat (Czech and Parsons, 2002); however, rice production is also associated with several negative impacts. First, rice requires higher water inputs than other cereal crops (Pimentel et al., 2004). Increasing food demand from a growing population and decreasing water availability (Mekonnen and Hoekstra, 2016) are placing pressure on rice growers to reduce the amount of water used for rice production. Second, the global warming potential of rice is elevated compared with other crops, caused in large part by high methane emissions (Linquist et al., 2012;Wassmann et al., 2010). Finally, flooded conditions can also change the speciation and increase the bioavailability of As and k. Christy Tanner* Core Ideas• We studied how alternate wetting and drying (AWd) water management effects methylmercury (MeHg) dynamics in rice fields.• Alternate wetting and drying reduced MeHg concentrations in soil, water, and rice grain.• Iron speciation indicated that AWd oxidized the soil and regenerated electron acceptors.• Rice yield did not differ between AWd and the control over 4 yr.

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Deposition of mercury in forests across a montane elevation gradient: Elevational and seasonal patterns in methylmercury inputs and production

et al. 2017

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Global mercury contamination largely results from direct primary atmospheric and secondary legacy emissions, which can be deposited to ecosystems, converted to methylmercury, and bioaccumulated along food chains. We examined organic horizon soil samples collected across an elevational gradient on Whiteface Mountain in the Adirondack region of New York State, USA to determine spatial patterns in methylmercury concentrations across a forested montane landscape. We found that soil methylmercury concentrations were highest in the midelevation coniferous zone (0.39 ± 0.07 ng/g) compared to the higher elevation alpine zone (0.28 ± 0.04 ng/g) and particularly the lower elevation deciduous zone (0.17 ± 0.02 ng/g), while the percent of total mercury as methylmercury in soils decreased with elevation. We also found a seasonal pattern in soil methylmercury concentrations, with peak methylmercury values occurring in July. Given elevational patterns in temperature and bioavailable total mercury (derived from mineralization of soil organic matter), soil methylmercury concentrations appear to be driven by soil processing of ionic Hg, as opposed to atmospheric deposition of methylmercury. These methylmercury results are consistent with spatial patterns of mercury concentrations in songbird species observed from other studies, suggesting that future declines in mercury emissions could be important for reducing exposure of mercury to montane avian species.

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Global prevalence and distribution of genes and microorganisms involved in mercury methylation

Abstract: A global metagenome assessment reveals a low risk of methylmercury production in humans and a high potential in Arctic permafrost.

Cited by 379 publications

References 69 publications

Recent advances in the study of mercury methylation in aquatic systems

Recent advances in the study of mercury methylation in aquatic systems

Alternate Wetting and Drying Decreases Methylmercury in Flooded Rice (Oryza sativa) Systems

Deposition of mercury in forests across a montane elevation gradient: Elevational and seasonal patterns in methylmercury inputs and production

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