| 1. |
- Capo, Eric, et al.
(författare)
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Deltaproteobacteria andSpirochaetes-Like Bacteria AreAbundant Putative MercuryMethylators in Oxygen-DeficientWater and Marine Particles in theBaltic Sea
- 2020
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; , s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Methylmercury (MeHg), a neurotoxic compound biomagnifying in aquatic food webs, can be a threat to human health via fish consumption. However, the compositionand distribution of the microbial communities mediating the methylation of mercury (Hg) to MeHg in marine systems remain largely unknown. In order to fill this knowledge gap, we used the Baltic Sea Reference Metagenome (BARM) dataset to study the abundance and distribution of the genes involved in Hg methylation (the hgcAB gene cluster). We determined the relative abundance of the hgcAB genes and their taxonomic identity in 81 brackish metagenomes that cover spatial,seasonal and redox variability in the Baltic Sea water column. The hgcAB genes were predominantly detected in anoxic water, but some hgcAB genes were alsodetected in hypoxic and normoxic waters. Phylogenetic analysis identified putative Hg methylators within Deltaproteobacteria, in oxygen-deficient water layers, but also Spirochaetes-like and Kiritimatiellaeota-like bacteria. Higher relative quantities of hgcAB genes were found in metagenomes from marine particles compared to free-living communities in anoxic water, suggesting that such particles are hotspot habitats for Hg methylators in oxygen-depleted seawater. Altogether, our work unveils the diversityof the microorganisms with the potential to mediate MeHg production in the BalticSea and pinpoint the important ecological niches for these microorganisms within themarine water column.
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| 2. |
- Capo, Eric, et al.
(författare)
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Expression Levels of hgcAB Genes and Mercury Availability Jointly Explain Methylmercury Formation in Stratified Brackish Waters
- 2022
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:18, s. 13119-13130
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Tidskriftsartikel (refereegranskat)abstract
- Neurotoxic methylmercury (MeHg) is formed by microbial methylation of inorganic divalent Hg (Hg-II) and constitutes severe environmental and human health risks. The methylation is enabled by hgcA and hgcB genes, but it is not know nif the associated molecular-level processes are rate-limiting or enable accurate prediction of MeHg formation in nature. In this study, we investigated the relationships between hgc genes and MeHg across redox-stratified water columns in the brackish Baltic Sea. We showed, for the first time, that hgc transcript abundance and the concentration of dissolved Hg-II-sulfide species were strong predictors of both the Hg-II methylation rate and MeHg concentration, implying their roles as principal joint drivers of MeHg formation in these systems. Additionally, we characterized the metabolic capacities of hgc(+) microorganisms by reconstructing their genomes from metagenomes (i.e., hgc(+) MAGs), which highlighted the versatility of putative Hg-II methylators in the water column of the Baltic Sea. In establishing relationships between hgc transcripts and the Hg-II methylation rate, we advance the fundamental understanding of mechanistic principles governing MeHg formation in nature and enable refined predictions of MeHg levels in coastal seas in response to the accelerating spread of oxygen-deficientzones.
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| 3. |
- Huynh, Khoa, et al.
(författare)
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Quantification of total concentration of thiol functional groups in environmental samples by titration with monobromo(trimethylammonio) bimane and determination with tandem mass spectrometry
- 2020
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Ingår i: Talanta. - : Elsevier. - 0039-9140 .- 1873-3573. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- Thiol compounds (R–SH) have many important biological functions and are principal controls of the speciation of several toxic metals in the environment. However, determining the concentration of thiols associated with environmental matrices is challenging due to the compounds’ low abundance and interferences from non-thiol compounds for many available methods. Here a novel method has been developed and validated to quantify the total concentration of thiol functional groups in aqueous samples using derivatization with monobromo(trimethylammonio)bimane (qBBr) and quantification with tandem mass spectrometry. The thiol concentration was determined by titration of the sample with qBBr, which reacts selectively with thiols, and quantification of the residual qBBr. We systematically evaluated potential interferences from various organic compounds, inorganic ions (including sea water matrices), sulfide and mercury (Hg) species, and demonstrate that the method is highly sensitive, selective and robust. The limit of detection (LOD) for total thiols is in the nanomolar concentration range (~6 nM). The method performance was also demonstrated by determination of the total thiol concentration in different natural samples including boreal stream water (1.16 μM), wetland porewater (0.96 μM) and the Suwanee River natural organic matter (NOM) reference material SR101 N (7.9 μmol g−1). The developed method represents a combination of low LOD and high selectivity and robustness that is unsurpassed for total thiol concentration measurements.
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