| 1. |
- Beier, Sara, et al.
(författare)
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Global Phylogeography of Chitinase Genes in Aquatic Metagenomes
- 2011
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 77:3, s. 1101-1106
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Tidskriftsartikel (refereegranskat)abstract
- Phylogeny-based analysis of chitinase and 16S rRNA genes from metagenomic data suggests that salinity is a major driver for the distribution of both chitinolytic and total bacterial communities in aquatic systems. Additionally, more acidic chitinase proteins were observed with increasing salinity. Congruent habitat separation was further observed for both genes according to latitude and proximity to the coastline. However, comparison of chitinase and 16S rRNA genes extracted from different geographic locations showed little congruence in distribution. There was no indication that dispersal limited the global distribution of either gene.
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| 2. |
- Eklöf, Karin, et al.
(författare)
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Formation of mercury methylation hotspots as a consequence of forestry operations
- 2018
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 613-614, s. 1069-1078
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Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have shown that boreal forest logging can increase the concentration and export of methylmercury (MeHg) in stream runoff. Here we test whether forestry operations create soil environments of high MeHg net formation associated with distinct microbial communities. Furthermore, we test the hypothesis that Hg methylation hotspots are more prone to form after stump harvest than stem-only harvest, because of more severe soil compaction and soil disturbance. Concentrations of MeHg, percent MeHg of total Hg (THg), and bacterial community composition were determined at 200 soil sampling positions distributed across eight catchments. Each catchment was either stem-only harvested (n = 3), stem-and stump-harvested (n = 2) or left undisturbed (n = 3). In support of our hypothesis, higher MeHg to THg ratios was observed in one of the stump-harvested catchments. While the effects of natural variation could not be ruled out, we noted that most of the highest % MeHg was observed in water-filled cavities created by stump removal or driving damage. This catchment also featured the highest bacterial diversity and highest relative abundance of bacterial families known to include Hg methylators. We propose that water-logged and disturbed soil environments associated with stump harvest can favor methylating microorganisms, which also enhance MeHg formation.
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| 3. |
- Jingying, Xu, 1984-, et al.
(författare)
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Mercury methylating microbial communities of boreal forest soils
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The formation of the potent neurotoxic methylmercury (MeHg) is a microbially mediated process that has raised much concern because MeHg poses threats to wildlife and human health. Since boreal forest soils can be a source of MeHg in aquatic networks, it is crucial to understand the biogeochemical processes involved in the formation of this pollutant. High-throughput sequencing of 16S rRNA and the mercury methyltransferase, hgcA, combined with geochemical characterisation of soils, were used to determine the microbial populations contributing to MeHg formation in forest soils across Sweden. The hgcA sequences obtained were distributed among diverse clades, including Proteobacteria, Firmicutes, and Methanomicrobia, with Deltaproteobacteria, particularly Geobacteraceae, dominating the libraries across all soils examined. Our results also suggest that MeHg formation is linked to the composition of also non-mercury methylating bacterial communities, likely providing growth substrate (e.g. acetate) for the hgcA-carrying microorganisms responsible for the actual methylation process. While previous research focused on mercury methylating microbial communities of wetlands, this study provides some first insights into the diversity of mercury methylating microorganisms in boreal forest soils.
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| 4. |
- Lundqvist, Anna, et al.
(författare)
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Effects of extracellular polymeric and humic substances on chlorpyrifos bioavailability to Chironomus riparius
- 2010
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Ingår i: Ecotoxicology. - : Springer Science and Business Media LLC. - 0963-9292 .- 1573-3017. ; 19:4, s. 614-622
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Tidskriftsartikel (refereegranskat)abstract
- The role of sediment organic matter quality and quantity for chlorpyrifos bioavailability was studied in experiments with Chironomus riparius larvae and with four types of organic matter; (1) commercially available extracellular polymeric substances (EPS), (2) EPS produced by sediment microbes, (3) commercially available humic substances and, (4) humic substances extracted from a boreal lake. The effects of each type of organic matter were assessed at three concentrations. We used a C-14-tracer approach to quantify uptake of chlorpyrifos in the larvae, and the partitioning of the insecticide within the microcosm. Carbon-normalised larval uptake was reduced both by EPS and humic substances. However, the reduction in uptake was much greater for EPS than for humic substances: uptake was reduced by 94 and 88% for commercial and complex EPS, and by 59 and 57% for commercial and complex humic substances, respectively. We also found differences in chlorpyrifos uptake, and sediment concentrations between treatments with commercially available and complex polymers, suggesting that minor differences in the quality of relatively simple organic molecules can affect contaminant behaviour in ecotoxicological studies. Passive uptake in dead controls was 40% of that in living larvae. Therefore, both passive and digestive uptake were important processes for chlorpyrifos uptake by larvae. Our results show that both EPS and humic substances affect chlorpyrifos bioavailability to sediment biota negatively and contribute to the understanding of the processes that regulate organic contaminant bioavailability in aquatic environments.
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| 5. |
- Nota, Kevin, 1993-, et al.
(författare)
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Norway spruce postglacial recolonization of Fennoscandia
- 2022
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Contrasting theories exist regarding how Norway spruce (Picea abies) recolonized Fennoscandia after the last glaciation and both early Holocene establishments from western microrefugia and late Holocene colonization from the east have been postulated. Here, we show that Norway spruce was present in southern Fennoscandia as early as 14.7 ± 0.1 cal. kyr BP and that the millennia-old clonal spruce trees present today in central Sweden likely arrived with an early Holocene migration from the east. Our findings are based on ancient sedimentary DNA from multiple European sites (N = 15) combined with nuclear and mitochondrial DNA analysis of ancient clonal (N = 135) and contemporary spruce forest trees (N = 129) from central Sweden. Our other findings imply that Norway spruce was present shortly after deglaciation at the margins of the Scandinavian Ice Sheet, and support previously disputed finds of pollen in southern Sweden claiming spruce establishment during the Lateglacial.
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| 6. |
- Catalán, Núria, 1985-, et al.
(författare)
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Effects of beaver impoundments on dissolved organic matter quality and biodegradability in boreal riverine systems
- 2017
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 793:1, s. 135-148
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Tidskriftsartikel (refereegranskat)abstract
- Beaver impoundments modify the structure of river reaches and lead to changes in ecosystem function and biogeochemical processes. Here, we assessed the changes in dissolved organic matter (DOM) quality and the biodegradation patterns in a set of beaver systems across Sweden. As the effect of beaver impoundments might be transient and local, we compared DOM quality and biodegradability of both pond and upstream sections of differentially aged beaver systems. Newly established dams shifted the sources and DOM biodegradability patterns. In particular, humic-like DOM, most likely leached from surrounding soils, characterized upstream sections of new beaver impoundments. In contrast, autochthonous and processed compounds, with both higher biodegradation rates and a broader spectrum of reactivities, differentiated DOM in ponds. DOM in recently established ponds seemed to be more humic and less processed compared to older ponds, but system idiosyncrasies determined by catchment particularities influenced this ageing effect.
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| 7. |
- Hu, Haiyan, et al.
(författare)
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Shifts in mercury methylation across a peatland chronosequence : From sulfate reduction to methanogenesis and syntrophy
- 2020
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Ingår i: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 387
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Tidskriftsartikel (refereegranskat)abstract
- Peatlands are globally important ecosystems where inorganic mercury is converted to bioaccumulating and highly toxic methylmercury, resulting in high risks of methylmercury exposure in adjacent aquatic ecosystems. Although biological mercury methylation has been known for decades, there is still a lack of knowledge about the organisms involved in mercury methylation and the drivers controlling their methylating capacity. In order to investigate the metabolisms responsible for mercury methylation and methylmercury degradation as well as the controls of both processes, we studied a chronosequence of boreal peatlands covering fundamentally different biogeochemical conditions. Potential mercury methylation rates decreased with peatland age, being up to 53 times higher in the youngest peatland compared to the oldest. Methylation in young mires was driven by sulfate reduction, while methanogenic and syntrophic metabolisms became more important in older systems. Demethylation rates were also highest in young wetlands, with a gradual shift from biotic to abiotic methylmercury degradation along the chronosequence. Our findings reveal how metabolic shifts drive mercury methylation and its ratio to demethylation as peatlands age.
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| 8. |
- Jingying, Xu, 1984-, et al.
(författare)
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Mercury Methylating Microbial Community Structure in Boreal Wetlands Explained by Local Physicochemical Conditions
- 2021
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Ingår i: Frontiers in Environmental Science. - : Frontiers Media S.A.. - 2296-665X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The potent neurotoxin methylmercury (MeHg) is a major concern due to its negative effects on wildlife and human health. Boreal wetlands play a crucial role in Hg cycling on a global scale, and therefore, it is crucial to understand the biogeochemical processes involved in MeHg formation in this landscape element. By combining high-throughput hgcA amplicon sequencing with molecular barcoding, we reveal diverse clades of potential Hg-II methylators in a wide range of wetland soils. Among Bacteria, Desulfuromonadota (14% of total reads), Desulfurobacterota_A, and Desulfurobacterota (up to 6% of total reads), previously classified as Deltaproteobacteria, were important members of the hgcA+ microbial community in the studied wetlands. We also identified Actinobacteriota (9.4% of total reads), Bacteroidota (2% of total reads), and Firmicutes (1.2% of total reads) as members of the hgcA+ microbial community. Within Archaea, Methanosarcinales represented up to 2.5% of the total reads. However, up to half of the hgcA+ community could not be resolved beyond domain Bacteria. Our survey also shows that local physicochemical conditions, such as pH, nutrient concentrations, water content, and prevailing redox states, are important for shaping the hgcA+ microbial community structure across the four studied wetlands. Furthermore, we observed a significant correlation between Hg-II methylation rate constants and the structure of the hgcA+ microbial community. Our findings expand the current knowledge on the hgcA+ microbial community composition in wetlands and the physicochemical factors underpinning spatial heterogeneity in such communities.
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| 9. |
- Segura, Javier, et al.
(författare)
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Microbial utilization of simple carbon substrates in boreal peat soils at low temperatures
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 135, s. 438-448
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Tidskriftsartikel (refereegranskat)abstract
- Boreal peatlands are key high-latitude ecosystem types and act as a carbon (C) sink storing an estimated 25% of the world's soil C. These environments are currently seeing the most substantial changing climate, especially during the winter. CO2 emissions during the winter can correspond to 80% of the growing season's net CO2 assimilation. Yet, our conceptual understanding of the controls on microbial metabolic activity in peat soils at temperatures ≤0 °C is poor. We used stable isotope probing of peat samples and tracked the fate of 13C-glucose using 13C-NMR. We show that microorganisms in frozen boreal peat soils utilize monomeric C-substrates to sustain both catabolic and anabolic metabolism at temperatures down to −5 °C. The 13C-substrate was transformed into 13C–CO2, different metabolites, and incorporated into membrane phospholipid fatty acids. The 16S rRNA-based community analyses revealed the activity at −3 °C changes the composition of the bacterial community over relevant timescales. Below 0 °C, small temperature changes have strong effects on process rates and small differences in winter soil temperature may affect C dynamics of northern peatlands. Understanding biological processes at low and below zero temperatures are central for the overall functioning of these systems representing one of the world's major soil C pools.
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| 10. |
- Söderqvist, Karin, et al.
(författare)
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Emerging microbiota during cold storage and temperature abuse of ready-to-eat salad
- 2017
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Ingår i: Infection Ecology & Epidemiology. - : Informa UK Limited. - 2000-8686 .- 2000-8686. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Ready-to-eat (RTE) leafy vegetables have a natural leaf microbiota that changes during different processing and handling steps from farm to fork. The objectives of this study were (i) to compare the microbiota of RTE baby spinach and mixed-ingredient salad before and after seven days of storage at 8°C or 15°C; (ii) to explore associations between bacterial communities and the foodborne pathogens Listeria monocytogenes, pathogenic Yersinia enterocolitica, and pathogen model organism Escherichia coli O157:H7 gfp+ when experimentally inoculated into the salads before storage; and (iii) to investigate if bacterial pathogens may be detected in the 16S rRNA amplicon dataset. Material and methods: The microbiota was studied by means of Illumina 16S rRNA amplicon sequencing. Subsets of samples were inoculated with low numbers (50-100 CFU g(-1)) of E. coli O157:H7 gfp+, pathogenic Y. enterocolitica or L. monocytogenes before storage. Results and discussion: The composition of bacterial communities changed during storage of RTE baby spinach and mixed-ingredient salad, with Pseudomonadales as the most abundant order across all samples. Although pathogens were present at high viable counts in some samples, they were only detected in the community-wide dataset in samples where they represented approximately 10% of total viable counts. Positive correlations were identified between viable counts of inoculated strains and the abundance of Lactobacillales, Enterobacteriales, and Bacillales, pointing to positive interactions or similar environmental driver variables that may make it feasible to use such bacterial lineages as indicators of microbial health hazards in leafy vegetables. The data from this study contribute to a better understanding of the bacteria present in RTE salads and may help when developing new types of biocontrol agents.
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