Relative contributions of mercury bioavailability and microbial growth rate on net methylmercury production by anaerobic mixed cultures

Kucharzyk, Katarzyna H.; Deshusses, Marc A.; Porter, Kaitlyn A.; Hsu‐Kim, Heileen

doi:10.1039/c5em00174a

Cited by 22 publications

(26 citation statements)

References 42 publications

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“…Recent developments of the use of stable isotope tracers and geonomic work have begun to examine the synergies of multiple factors. For example, Keucharzyk et al (2015) found that methylation rates in marine sediments were highest when mixed cell cultures were amended with carbon, regardless of whether inorganic Hg was added as dissolved nitrate salt or as nanoparticles of HgS (as also observed by Graham et al (2013); see above). Similarly, nutrient loading that stimulated microbial activity indirectly by increasing phytoplankton biomass was as important as bioavailability of Hg available to methylators (Liem-Nguyen et al 2016).…”

Section: How Do We Deal With So Many Confounding Factors?mentioning

confidence: 70%

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: How Do We Deal With So Many Confounding Factors?mentioning

confidence: 70%

Recent advances in the study of mercury methylation in aquatic systems

Paranjape

Hall

2017

FACETS

121

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“…The MeHg production potential (MPP) by microbial communities is also impacted by geochemistry (e.g., pH) ( 19 ), hydrology ( 47 ), Hg and MeHg concentrations and bioavailability, and net accumulation of MeHg ( 48 ). MPP is the amount of MeHg produced per day (micrograms of MeHg per kilogram of THg spiked per day).…”

Section: Methodsmentioning

confidence: 99%

Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments

Christensen

Somenahally

Moberly

et al. 2018

Appl Environ Microbiol

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Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the genes hgcAB, but it is unknown how organic substrate and electron acceptor availability impacts the distribution and abundance of these organisms. We evaluated the impact of organic substrate amendments on mercury (Hg) methylation rates, microbial community structure, and the distribution of hgcAB+ microbes with sediments. Sediment slurries were amended with short-chain fatty acids, alcohols, or a polysaccharide. Minimal increases in MeHg were observed following lactate, ethanol, and methanol amendments, while a significant decrease (∼70%) was observed with cellobiose incubations. Postincubation, microbial diversity was assessed via 16S rRNA amplicon sequencing. The presence of hgcAB+ organisms was assessed with a broad-range degenerate PCR primer set for both genes, while the presence of microbes in each of the three dominant clades of methylators (Deltaproteobacteria, Firmicutes, and methanogenic Archaea) was measured with clade-specific degenerate hgcA quantitative PCR (qPCR) primer sets. The predominant microorganisms in unamended sediments consisted of Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. Clade-specific qPCR identified hgcA+ Deltaproteobacteria and Archaea in all sites but failed to detect hgcA+ Firmicutes. Cellobiose shifted the communities in all samples to ∼90% non-hgcAB-containing Firmicutes (mainly Bacillus spp. and Clostridium spp.). These results suggest that either expression of hgcAB is downregulated or, more likely given the lack of 16S rRNA gene presence after cellobiose incubation, Hg-methylating organisms are largely outcompeted by cellobiose degraders or degradation products of cellobiose. These results represent a step toward understanding and exploring simple methodologies for controlling MeHg production in the environment.IMPORTANCE Methylmercury (MeHg) is a neurotoxin produced by microorganisms that bioacummulates in the food web and poses a serious health risk to humans. Currently, the impact that organic substrate or electron acceptor availability has on the mercury (Hg)-methylating microorganisms is unclear. To study this, we set up microcosm experiments exposed to different organic substrates and electron acceptors and assayed for Hg methylation rates, for microbial community structure, and for distribution of Hg methylators. The sediment and groundwater was collected from East Fork Poplar Creek in Oak Ridge, TN. Amendment with cellobiose (a lignocellulosic degradation by-product) led to a drastic decrease in the Hg methylation rate compared to that in an unamended control, with an associated shift in the microbial community to mostly nonmethylating Firmicutes. This, along with previous Hg-methylating microorganism identification methods, will be important for identifying strategies to control MeHg production and inform future remediation strategies.

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“…These changes affect redox gradients which can result in increased MeHg production (Driscoll et al 1995 ; Slotton et al 1995 ; Watras et al 1995 ; Herrin et al 1998 ; Eckley and Hintelmann 2006 ; Merritt and Amirbahman 2008 ). Chelation of inorganic Hg(II) by NOM has the potential to lower the bioavailability of Hg for methylation; however, this effect might be masked by stimulation of Hg methylators, depending on the type of NOM (Drott et al 2007 ; Kim et al 2011 ; Gascón Díez et al 2016 ; Mazrui et al 2016 ; Bravo et al 2017 ) and the limiting factor for net Hg methylation (e.g., Hg speciation, productivity of methylators, or demethylation processes) (Jonsson et al 2012 ; Zhang et al 2014b ; Kucharzyk et al 2015 ; Liem-Nguyen et al 2016 ). Organic matter loads also influence the structure of pelagic food webs, with secondary impacts on MeHg biomagnification (Jonsson et al 2017 ).…”

Section: Altered Surface Loadingsmentioning

confidence: 99%

Challenges and opportunities for managing aquatic mercury pollution in altered landscapes

Hsu‐Kim

Eckley

Achá

et al. 2018

Ambio

Self Cite

208

115

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The environmental cycling of mercury (Hg) can be affected by natural and anthropogenic perturbations. Of particular concern is how these disruptions increase mobilization of Hg from sites and alter the formation of monomethylmercury (MeHg), a bioaccumulative form of Hg for humans and wildlife. The scientific community has made significant advances in recent years in understanding the processes contributing to the risk of MeHg in the environment. The objective of this paper is to synthesize the scientific understanding of how Hg cycling in the aquatic environment is influenced by landscape perturbations at the local scale, perturbations that include watershed loadings, deforestation, reservoir and wetland creation, rice production, urbanization, mining and industrial point source pollution, and remediation. We focus on the major challenges associated with each type of alteration, as well as management opportunities that could lessen both MeHg levels in biota and exposure to humans. For example, our understanding of approximate response times to changes in Hg inputs from various sources or landscape alterations could lead to policies that prioritize the avoidance of certain activities in the most vulnerable systems and sequestration of Hg in deep soil and sediment pools. The remediation of Hg pollution from historical mining and other industries is shifting towards in situ technologies that could be less disruptive and less costly than conventional approaches. Contemporary artisanal gold mining has well-documented impacts with respect to Hg; however, significant social and political challenges remain in implementing effective policies to minimize Hg use. Much remains to be learned as we strive towards the meaningful application of our understanding for stakeholders, including communities living near Hg-polluted sites, environmental policy makers, and scientists and engineers tasked with developing watershed management solutions. Site-specific assessments of MeHg exposure risk will require new methods to predict the impacts of anthropogenic perturbations and an understanding of the complexity of Hg cycling at the local scale.Electronic supplementary materialThe online version of this article (10.1007/s13280-017-1006-7) contains supplementary material, which is available to authorized users.

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Relative contributions of mercury bioavailability and microbial growth rate on net methylmercury production by anaerobic mixed cultures

Cited by 22 publications

References 42 publications

Recent advances in the study of mercury methylation in aquatic systems

Recent advances in the study of mercury methylation in aquatic systems

Carbon Amendments Alter Microbial Community Structure and Net Mercury Methylation Potential in Sediments

Challenges and opportunities for managing aquatic mercury pollution in altered landscapes

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