| 1. |
- Bravo, Andrea Garcia, et al.
(författare)
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Geobacteraceae are important members of mercury-methylating microbial communities of sediments impacted by waste water releases
- 2018
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 12, s. 802-812
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Tidskriftsartikel (refereegranskat)abstract
- Microbial mercury (Hg) methylation in sediments can result in bioaccumulation of the neurotoxin methylmercury (MMHg) in aquatic food webs. Recently, the discovery of the gene hgcA, required for Hg methylation, revealed that the diversity of Hg methylators is much broader than previously thought. However, little is known about the identity of Hg-methylating microbial organisms and the environmental factors controlling their activity and distribution in lakes. Here, we combined high-throughput sequencing of 16S rRNA and hgcA genes with the chemical characterization of sediments impacted by a waste water treatment plant that releases significant amounts of organic matter and iron. Our results highlight that the ferruginous geochemical conditions prevailing at 1–2 cm depth are conducive to MMHg formation and that the Hgmethylating guild is composed of iron and sulfur-transforming bacteria, syntrophs, and methanogens. Deltaproteobacteria, notably Geobacteraceae, dominated the hgcA carrying communities, while sulfate reducers constituted only a minor component, despite being considered the main Hg methylators in many anoxic aquatic environments. Because iron is widely applied in waste water treatment, the importance of Geobacteraceae for Hg methylation and the complexity of Hgmethylating communities reported here are likely to occur worldwide in sediments impacted by waste water treatment plant discharges and in iron-rich sediments in general.
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| 2. |
- Bravo, Andrea G., et al.
(författare)
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Persistent Hg contamination and occurrence of Hg-methylating transcript (hgcA) downstream of a chlor-alkali plant in the Olt River (Romania)
- 2016
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Ingår i: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 23:11, s. 10529-10541
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Tidskriftsartikel (refereegranskat)abstract
- Chlor-alkali plants using mercury (Hg) cell technology are acute point sources of Hg pollution in the aquatic environment. While there have been recent efforts to reduce the use of Hg cells, some of the emitted Hg can be transformed to neurotoxic methylmercury (MeHg). Here, we aimed (i) to study the dispersion of Hg in four reservoirs located downstream of a chlor-alkali plant along the Olt River (Romania) and (ii) to track the activity of bacterial functional genes involved in Hg methylation. Total Hg (THg) concentrations in water and sediments decreased successively from the initial reservoir to downstream reservoirs. Suspended fine size particles and seston appeared to be responsible for the transport of THg into downstream reservoirs, while macrophytes reflected the local bioavailability of Hg. The concentration and proportion of MeHg were correlated with THg, but were not correlated with bacterial activity in sediments, while the abundance of hgcA transcript correlated with organic matter and Cl- concentration, indicating the importance of Hg bioavailability in sediments for Hg methylation. Our data clearly highlights the importance of considering Hg contamination as a legacy pollutant since there is a high risk of continued Hg accumulation in food webs long after Hg-cell phase out.
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| 3. |
- Capo, Eric, et al.
(författare)
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A consensus protocol for the recovery of mercury methylation genes from metagenomes
- 2023
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Ingår i: Molecular Ecology Resources. - : John Wiley & Sons. - 1755-098X .- 1755-0998. ; 23:1, s. 190-204
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) methylation genes (hgcAB) mediate the formation of the toxic methylmercury and have been identified from diverse environments, including freshwater and marine ecosystems, Arctic permafrost, forest and paddy soils, coal-ash amended sediments, chlor-alkali plants discharges and geothermal springs. Here we present the first attempt at a standardized protocol for the detection, identification and quantification of hgc genes from metagenomes. Our Hg-cycling microorganisms in aquatic and terrestrial ecosystems (Hg-MATE) database, a catalogue of hgc genes, provides the most accurate information to date on the taxonomic identity and functional/metabolic attributes of microorganisms responsible for Hg methylation in the environment. Furthermore, we introduce "marky-coco", a ready-to-use bioinformatic pipeline based on de novo single-metagenome assembly, for easy and accurate characterization of hgc genes from environmental samples. We compared the recovery of hgc genes from environmental metagenomes using the marky-coco pipeline with an approach based on coassembly of multiple metagenomes. Our data show similar efficiency in both approaches for most environments except those with high diversity (i.e., paddy soils) for which a coassembly approach was preferred. Finally, we discuss the definition of true hgc genes and methods to normalize hgc gene counts from metagenomes.
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| 4. |
- Capo, Eric, et al.
(författare)
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Anaerobic mercury methylators inhabit sinking particles of oxic water columns
- 2023
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Ingår i: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- Increased concentration of mercury, particularly methylmercury, in the environment is a worldwide concern because of its toxicity in severely exposed humans. Although the formation of methylmercury in oxic water columns has been previously suggested, there is no evidence of the presence of microorganisms able to perform this process, using the hgcAB gene pair (hgc+ microorganisms), in such environments. Here we show the prevalence of hgc+ microorganisms in sinking particles of the oxic water column of Lake Geneva (Switzerland and France) and its anoxic bottom sediments. Compared to anoxic sediments, sinking particles found in oxic waters exhibited relatively high proportion of hgc+genes taxonomically assigned to Firmicutes. In contrast hgc+members from Nitrospirae, Chloroflexota and PVC superphylum were prevalent in anoxic sediment while hgc+ Desulfobacterota were found in both environments. Altogether, the description of the diversity of putative mercury methylators in the oxic water column expand our understanding on MeHg formation in aquatic environments and at a global scale.
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| 5. |
- Garcia Bravo, Andrea, et al.
(författare)
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Extremely elevated methyl mercury levels in water, sediment and organisms in a Romanian reservoir affected by release of mercury from a chlor-alkali plant
- 2014
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 49, s. 391-405
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Tidskriftsartikel (refereegranskat)abstract
- We examined mercury (Hg) biogeochemistry and biomagnification in the Babeni Reservoir, a system strongly affected by the release of Hg from a chlor-alkali plant. Total mercury (THg) concentrations in river water reached 88 ng L−1 but decreased rapidly in the reservoir (to 9 ng L−1). In contrast, monomethylmercury (MMHg) concentrations increased from the upstream part of the reservoir to the central part (0.7 ng L−1), suggesting high methylation within the reservoir. Moreover, vertical water column profiles of THg and MMHg indicated that Hg methylation mainly occurred deep in the water column and at the sediment–water interface. The discharge of Hg from a chlor-alkali plant in Valcea region caused the highest MMHg concentrations ever found in non-piscivorous fish worldwide. MMHg concentrations and bioconcentration factors (BCF) of plankton and macrophytes revealed that the highest biomagnification of MMHg takes place in primary producers.
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| 6. |
- Gascon Diez, Elena, et al.
(författare)
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Role of settling particles on mercury methylation in the oxic water 1 column of freshwater systems
- 2016
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 50:21, s. 11672-11679
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Tidskriftsartikel (refereegranskat)abstract
- As the methylation of inorganic divalent mercury (HgII) to neurotoxic methylmercury (MeHg) has been attributed to the activity of anaerobic bacteria, the formation of MeHg in the oxic water column of marine ecosystems has puzzled scientists over the past years. Here we show for the first time that MeHg can be produced in particles sinking through oxygenated water column of lakes. Total mercury (THg) and MeHg concentrations were measured in settling particles and in surface sediments of the largest freshwater lake in Western Europe (Lake Geneva). Whilst THg concentration differences between sediments and settling particles were not significant, MeHg concentrations were up to ten-fold greater in settling particles. MeHg demethylation rate constants (kd) were of similar magnitude in both compartments. In contrast, Hg methylation rate constants (km) were one order of magnitude greater in settling particles. The net potential for MeHg formation, assessed by the ratio between the two rate constants (km kd-1), was therefore up to ten times higher in settling particles, denoting that in situ transformations likely contributed to the high MeHg concentrations found in settling particles. Hg 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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