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- 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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| 2. |
- Skrobonja, Aleksandra, 1990-
(författare)
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Formation, uptake and bioaccumulation of methylmercury in coastal seas : a baltic sea case study
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methylmercury (MeHg) is a potent neurotoxin which can bioaccumulate to harmful levels in aquatic food webs. Methylmercury formation is a predominantly biotic process which involves phylogenically diverse microorganisms (e.g. iron- or sulfate-reducing bacteria). The formation of MeHg is related to the presence of organic matter (OM) which contains substrates essential for methylating microbes and reduced sulfur ligands (thiols, RSH) that form strong bonds with inorganic mercury (HgII) and affect its bioavailability. In aquatic systems, MeHg is bio-concentrated from the water column to the base of the food web and this step is crucial for MeHg levels found at higher trophic levels. Trophic transfer processes of MeHg in the food web are also of great importance. Discharge of OM in coastal areas affects light conditions needed for phytoplankton growth, and promotes heterotrophy, i.e. bacteria production. This may lead to a shift from the phytoplankton-based to the longer bacteria-based (microbial loop) food web and influence the amount of bioaccumulated MeHg in higher trophic levels. Methylmercury levels in predatory biota is thus affected by the bioavailability of HgII for methylation (studied in Paper I & II), MeHg speciation in the water column, crucial for MeHg incorporation at the base of the food web (Paper III), and the structure of the pelagic food web (Paper IV).In this thesis, it is shown that OM can act as a predictor of dissolved MeHg levels in estuarine and coastal systems. It impacts MeHg levels both by affecting HgII bioavailability (through Hg complexation with humic matter) and the activity of methylating microbes (providing metabolic electron donors) (Paper I). Moreover, elevated concentrations of particulate and dissolved HgII and MeHg, are associated with the presence of pelagic redoxclines in coastal seas. The redoxcline affects HgII speciation in the water column and its bioavailability for methylation (Paper II). It is further shown that the molecular structure of ligands in MeHg complexes affects the kinetics of MeHg uptake in phytoplankton. Rate constants for association of MeHg to the cell surface of a green algae were higher in treatments containing smaller thiol ligands of simpler structure than in treatments with larger thiols and more “branched” structure (Paper III). Finally, it is demonstrated that MeHg bioaccumulation in zooplankton can increase in systems with highly heterotrophic food webs and enhanced loadings of terrestrial OM (Paper IV). Such conditions are expected to occur in northern latitude coastal systems following climate changes.
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