| 1. |
- Adyari, Bob, et al.
(författare)
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Strong impact of micropollutants on prokaryotic communities at the horizontal but not vertical scales in a subtropical reservoir, China
- 2020
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 721
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Tidskriftsartikel (refereegranskat)abstract
- Micropollutants have become of great concern, because of their disrupting effects on the structure and function of microbial communities. However, little is known about the relative importance of trace micropollutants on the aquatic prokaryotic communities as compared to the traditional physico-chemical characteristics, especially at different spatial dimensions. Here, we investigated free-living (FL) and particle-associated (PA) prokaryotic communities in a subtropical water reservoir, China, across seasons at horizontal (surface water) and vertical (depth-profile) scales by using 16S rRNA gene amplicon sequencing. Our results showed that the shared variances of physico-chemicals and micropollutants explained majority of the spatial variations in prokaryotic communities, suggesting a strong joint effect of the two abiotic categories on reservoir prokaryotic communities. Micropollutants appeared to exert strong independent influence on the core sub-communities (i.e., abundant and wide-spread taxa) than on the satellite (i.e., less abundant and narrow-range taxa) counterparts. The pure effect of micropollutants on both core and satellite sub-communities from FL and PA fractions was similar to 1.5 folds greater than that of physico-chemical factors at the horizontal scale, whereas an opposite effect was observed at the vertical scale. Moreover, eight micropollutants including anti-fungal agents, antibiotics, bisphenol analogues, stimulant and UV-filter were identified as the major disrupting compounds with strong associations with core taxa of typical freshwater prokaryotes. Altogether, we concluded that the ecological disrupting effects of micropollutants on prokaryotic communities may vary along horizontal and vertical dimensions in freshwater ecosystems.
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| 2. |
- Broman, Elias, et al.
(författare)
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Microbial functional genes are driven by gradients in sediment stoichiometry, oxygen, and salinity across the Baltic benthic ecosystem
- 2022
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Ingår i: Microbiome. - : Springer Science and Business Media LLC. - 2049-2618. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Microorganisms in the seafloor use a wide range of metabolic processes, which are coupled to the presence of functional genes within their genomes. Aquatic environments are heterogenous and often characterized by natural physiochemical gradients that structure these microbial communities potentially changing the diversity of functional genes and its associated metabolic processes. In this study, we investigated spatial variability and how environmental variables structure the diversity and composition of benthic functional genes and metabolic pathways across various fundamental environmental gradients. We analyzed metagenomic data from sediment samples, measured related abiotic data (e.g., salinity, oxygen and carbon content), covering 59 stations spanning 1,145 km across the Baltic Sea. Results: The composition of genes and microbial communities were mainly structured by salinity plus oxygen, and the carbon to nitrogen (C:N) ratio for specific metabolic pathways related to nutrient transport and carbon metabolism. Multivariate analyses indicated that the compositional change in functional genes was more prominent across environmental gradients compared to changes in microbial taxonomy even at genus level, and indicate functional diversity adaptation to local environments. Oxygen deficient areas (i.e., dead zones) were more different in gene composition when compared to oxic sediments. Conclusions: This study highlights how benthic functional genes are structured over spatial distances and by environmental gradients and resource availability, and suggests that changes in, e.g., oxygenation, salinity, and carbon plus nitrogen content will influence functional metabolic pathways in benthic habitats. [MediaObject not available: see fulltext.]
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| 3. |
- Chen, Yundai, et al.
(författare)
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Treatment Trends, Effectiveness, and Safety of Statins on Lipid Goal Attainment in Chinese Percutaneous Coronary Intervention Patients : a Multicenter, Retrospective Cohort Study
- 2017
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Ingår i: Clinical Therapeutics. - : ELSEVIER. - 0149-2918 .- 1879-114X. ; 39:9, s. 1827-1839
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Limited data exist on the use of statins in Chinese patients with coronary artery disease (CAD) treated with percutaneous coronary intervention (PCI). We therefore conducted this study to observe the usage trend and the effectiveness of statins on LDL-C goal attainment and other lipid parameters among PCI-treated patients.Methods: This multicenter, retrospective, observational, longitudinal cohort study was conducted in PCI-treated patients with CAD between July 1, 2011, and February 28, 2015. Primary study outcomes included statin treatment pattern after PCI and proportion of patients achieving target (LDL-C) levels 1 month after PCI and initiating statin therapy.Findings: Data were analyzed for 2708 patients (mean age, 59 [10] years; median body mass index, 25.6 [4.0] kg/m(2)). From baseline to the end of 1 month, atorvastatin and rosuvastatin were the most prescribed statins; 20 mg and 10 mg were the most prescribed doses and therefore chosen for efficacy comparisons. In patients without dose changes, LDL-C reduction with rosuvastatin 10 mg was significantly greater compared with atorvastatin 20 mg (-0.67 mmol/L [from 2.44 mmol/L to 1.77 mmol/L] vs 0.54 mmol/L [from 2.40 mmol/L to 1.86 mmol/L]; P = 0.008). However, there was no difference in HDL-C, triglyceride, or total cholesterol values between groups. Age and LDL-C levels at baseline were significantly associated with target LDL-C achievement.
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| 4. |
- Deng, Min, et al.
(författare)
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Genome-wide association analyses in Han Chinese identify two new susceptibility loci for amyotrophic lateral sclerosis
- 2013
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 45:6, s. 697-
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Tidskriftsartikel (refereegranskat)abstract
- To identify susceptibility genes for amyotrophic lateral sclerosis (ALS), we conducted a genome-wide association study (GWAS) in 506 individuals with sporadic ALS and 1,859 controls of Han Chinese ancestry. Ninety top SNPs suggested by the current GWAS and 6 SNPs identified by previous GWAS were analyzed in an independent cohort of 706 individuals with ALS and 1,777 controls of Han Chinese ancestry. We discovered two new susceptibility loci for ALS at 1q32 (CAMK1G, rs6703183, P-combined = 2.92 x 10(-8), odds ratio (OR) = 1.31) and 22p11 (CABIN1 and SUSD2, rs8141797, P-combined = 2.35 x 10(-9), OR = 1.52). These two loci explain 12.48% of the overall variance in disease risk in the Han Chinese population. We found no association evidence for the previously reported loci in the Han Chinese population, suggesting genetic heterogeneity of disease susceptibility for ALS between ancestry groups. Our study identifies two new susceptibility loci and suggests new pathogenic mechanisms of ALS.
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| 5. |
- Iburg, Sven, et al.
(författare)
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Effects of Recreational Boating on Microbial and Meiofauna Diversity in Coastal Shallow Ecosystems of the Baltic Sea
- 2021
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Ingår i: mSphere. - 2379-5042. ; 6:5
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Tidskriftsartikel (refereegranskat)abstract
- Recreational boating can impact benthic ecosystems in coastal waters. Reduced height and cover of aquatic vegetation in shallow Baltic Sea inlets with high boat traffic have raised concerns about cascading effects on benthic communities in these ecosystems. Here, we characterized the diversity and composition of sediment-associated microbial and meiofaunal communities across five bays subjected to low and high degrees of boating activity and examined the community-environment relationships and association with bay morphometry. We found that recreational boating activity altered meiofauna alpha diversity and the composition of both micro- and meiobenthic communities, and there were strong correlations between community structure and morphometric variables like topographic openness, wave exposure, water surface area, and total phosphorous concentrations. Inlets with high boat traffic showed an increase of bacterial taxa like Hydrogenophilaceae and Burkholderiaceae. Several meiofauna taxa previously reported to respond positively to high levels of suspended organic matter were found in higher relative abundances in the bays with high boat traffic. Overall, our results show that morphometric characteristics of inlets are the strongest drivers of benthic diversity in shallow coastal environments. However, while the effects were small, we found significant effects of recreational boating on benthic community structure that should be considered when evaluating the new mooring projects.IMPORTANCE With the increase of recreational boating activity and development of boating infrastructure in shallow, wave-protected areas, there is growing concern for their impact on coastal ecosystems. In order to properly assess the effects and consider the potential for recovery, it is important to investigate microbial and meiofaunal communities that underpin the functioning of these ecosystems. Here, we present the first study that uses DNA metabarcoding to assess how benthic biodiversity in shallow coastal areas is impacted by recreational boating. Our study shows a relatively small, but significant, effect of recreational boating both on meiofauna alpha diversity and meiofauna and bacterial community composition. However, both meiofauna and bacterial community composition in shallow benthic habitats is mediated to a higher degree by abiotic variables, such as topographic openness, area or size of the inlets, and wave exposure. Despite the fact that the effects were small, such impacts on benthic biodiversity should be considered in the management of coastal shallow habitats.
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| 6. |
- Izabel-Shen, Dandan, et al.
(författare)
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Abundance-Occupancy Relationships Along Taxonomic Ranks Reveal a Consistency of Niche Differentiation in Marine Bacterioplankton With Distinct Lifestyles
- 2021
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Abundance-occupancy relationships (AORs) are an important determinant of biotic community dynamics and habitat suitability. However, little is known about their role in complex bacterial communities, either within a phylogenetic framework or as a function of niche breadth. Based on data obtained in a field study in the St. Lawrence Estuary, we used 16S rRNA gene sequencing to examine the vertical patterns, strength, and character of AORs for particle-attached and free-living bacterial assemblages. Free-living communities were phylogenetically more diverse than particle-attached communities. The dominant taxa were consistent in terms of their presence/absence but population abundances differed in surface water vs. the cold intermediate layer. Significant, positive AORs characterized all of the surveyed communities across all taxonomic ranks of bacteria, thus demonstrating an ecologically conserved trend for both free-living and particle-attached bacteria. The strength of the AORs was low at the species level but higher at and above the genus level. These results demonstrate that an assessment of the distributions and population densities of finely resolved taxa does not necessarily improve determinations of apparent niche differences in marine bacterioplankton communities at regional scales compared with the information inferred from a broad taxonomic classification.
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| 7. |
- Izabel-Shen, Dandan, et al.
(författare)
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Quality of phytoplankton deposition structures bacterial communities at the water-sediment interface
- 2021
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Ingår i: Molecular Ecology. - : John Wiley & Sons. - 0962-1083 .- 1365-294X. ; 30:14, s. 3515-3529
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Tidskriftsartikel (refereegranskat)abstract
- Phytoplankton comprises a large fraction of the vertical carbon flux to deep water via the sinking of particulate organic matter (POM). However, despite the importance of phytoplankton in the coupling of benthic-pelagic productivity, the extent to which its deposition in the sediment affects bacterial dynamics at the water-sediment interface is poorly understood. Here, we conducted a microcosm experiment in which varying mixtures of diatom and cyanobacteria, representing phytoplankton-derived POM of differing quality, served as inputs to sediment cores. Characterization of 16S rRNA gene of the bacterial communities at the water-sediment interface showed that bacterial alpha-diversity was not affected by POM addition, while bacterial beta-diversity changed significantly along the POM quality gradient, with the variation driven by changes in relative abundance rather than in taxon replacement. Analysing individual taxa abundances across the POM gradient revealed two distinct bacterial responses, in which taxa within either diatom- or cyanobacteria-favoured groups were more phylogenetically closely related to one another than other taxa found in the water. Moreover, there was little overlap in taxon identity between sediment and water communities, suggesting the minor role played by sediment bacteria in influencing the observed changes in bacterial communities in the overlying water. Together, these results showed that variability in phytoplankton-originated POM can impact bacterial dynamics at the water-sediment interface. Our findings highlight the importance of considering the potential interactions between phytoplankton and bacteria in benthic-pelagic coupling in efforts to understand the structure and function of bacterial communities under a changing climate.
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| 8. |
- Izabel-Shen, Dandan
(författare)
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Understanding response of microbial communities to saltwater intrusion through microcosms
- 2021
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Ingår i: Computational and Structural Biotechnology Journal. - : Elsevier BV. - 2001-0370. ; 19, s. 929-933
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Tidskriftsartikel (refereegranskat)abstract
- A central pursuit of microbial ecology is to accurately describe and explain the shifts in microbial community composition and function that occur in response to environmental changes. This goal requires a thorough understanding of the individual responses of different species and of the processes guiding the assembly of microbial populations similar in their response traits and corresponding functional traits. These research topics are addressed and synthesized in this Highlights, in four studies applying a traitbased framework to assess how environmental change affected the composition and functional performance of bacterioplankton of natural origin in microcosm experiments. The salinity of many aquatic environments is currently changing, due to climate change and anthropogenic activities. The mechanisms by which salinity influences community assembly, functional redundancy and functional genes involved in nitrogen cycle, and how dispersal modifies community outcome are explored in the four studies. Together, the findings of these case studies demonstrate the feasibility of using novel experiments in combination with integrative analyses of 16S rRNA and meta-'omic' data to address ecological questions. This combined approach has the potential to elucidate both the processes contributing to bacterial community assembly and the possible links between the compositional and functional changes that occur under shifting environmental conditions.
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| 9. |
- Lobo, Leonor Q., et al.
(författare)
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Salinity and resource availability as drivers of Baltic benthic fungal diversity
- 2024
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Ingår i: Environmental DNA. - : John Wiley & Sons. - 2637-4943. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Marine biodiversity consists of a complex network of organisms responsible for keeping the ecosystem's balance. Fungi are an understudied group of organisms despite their recognized importance for ecosystem processes and diversity. How fungi respond to environmental change remains poorly understood, especially in marine benthic habitats. The Baltic Sea is a brackish coastal ecosystem with steep environmental gradients in a relatively limited geographical area and is therefore a particularly good system to investigate the impact of different abiotic factors on benthic fungal diversity. This study used environmental DNA (eDNA) metabarcoding to analyze the spatial dynamics of benthic fungal diversity in the Baltic Sea and quantify the environmental drivers that shape these dynamics. Based on 59 stations spreading over 1145 km the results showed that benthic fungal communities were dominated by the phylum Chytridiomycota, and the fungal species Alphamyces chaetifer and Operculomyces laminatus from this phylum were the main drivers of the community structure dissimilarities observed between regions. Water depth and salinity were the main predictors of the benthic fungal community composition. The impact of nutrient availability was also significant, possibly related to the known role of Chytridiomycota species such as A. chaetifer and O. laminatus in nutrient cycling. Our results indicate that the benthic fungal diversity of the Baltic Sea is shaped by salinity gradients and nutrient availability and highlights that the current fungal biodiversity is at risk of species shift or decline with predicted changes in salinity due to climate change and intensified eutrophication.
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| 10. |
- Rocca, Jennifer D., et al.
(författare)
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Guided by Microbes : Applying Community Coalescence Principles for Predictive Microbiome Engineering
- 2021
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Ingår i: mSystems. - 2379-5077. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- Every seed germinating in soils, wastewater treatment, and stream confluence exemplify microbial community coalescence—the blending of previously isolated communities. Here, we present theoretical and experimental knowledge on how separated microbial communities mix, with particular focus on managed ecosystems. We adopt the community coalescence framework, which integrates metacommunity theory and meta-ecosystem dynamics, and highlight the prevalence of these coalescence events within microbial systems. Specifically, we (i) describe fundamental types of community coalescences using naturally occurring and managed examples, (ii) offer ways forward to leverage community coalescence in managed systems, and (iii) emphasize the importance of microbial ecological theory to achieving desired coalescence outcomes. Further, considering the massive dispersal events of microbiomes and their coalescences is pivotal to better predict microbial community dynamics and responses to disturbances. We conclude our piece by highlighting some challenges and unanswered question yet to be tackled.
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| 11. |
- Rodríguez-Gijón, Alejandro, 1996-, et al.
(författare)
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Linking prokaryotic genome size variation to metabolic potential and environment
- 2023
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Ingår i: ISME Communications. - : Springer Science and Business Media LLC. - 2730-6151. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- While theories and models have appeared to explain genome size as a result of evolutionary processes, little work has shown that genome sizes carry ecological signatures. Our work delves into the ecological implications of microbial genome size variation in benthic and pelagic habitats across environmental gradients of the brackish Baltic Sea. While depth is significantly associated with genome size in benthic and pelagic brackish metagenomes, salinity is only correlated to genome size in benthic metagenomes. Overall, we confirm that prokaryotic genome sizes in Baltic sediments (3.47 Mbp) are significantly bigger than in the water column (2.96 Mbp). While benthic genomes have a higher number of functions than pelagic genomes, the smallest genomes coded for a higher number of module steps per Mbp for most of the functions irrespective of their environment. Some examples of this functions are amino acid metabolism and central carbohydrate metabolism. However, we observed that nitrogen metabolism was almost absent in pelagic genomes and was mostly present in benthic genomes. Finally, we also show that Bacteria inhabiting Baltic sediments and water column not only differ in taxonomy, but also in their metabolic potential, such as the Wood-Ljungdahl pathway or the presence of different hydrogenases. Our work shows how microbial genome size is linked to abiotic factors in the environment, metabolic potential and taxonomic identity of Bacteria and Archaea within aquatic ecosystems.
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| 12. |
- Sandberg, Henrik, et al.
(författare)
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NEMOte BARCODing : Förbättrad miljöövervakning av Östersjöns bentiska ekosystem
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Förändringar av ekosystem och hot mot biologisk mångfald, samt de på denna mångfald vilande ekosystemtjänsterna, har skapat ett behov av mer robusta och kostnadseffektiva miljöövervakningsmetoder. Projektet NEMOte BARCODing har undersökt om de frilevande nematoderna kan hjälpa oss att fylla detta behov. Metastreckkodning (metabarcoding på engelska), en av de moderna DNA-metoderna, har möjliggjort att meiofauna-organismer som nematoder effektiv kan provtas. Nematoderna är en av de mest mångfaldshaltiga organismgrupperna i världen, och de har visat sig vara bra indikatorer på ekosystems hälsa och förändringar i miljön. I Östersjön, där traditionellt enbart större organismer, makrofauna, har använts, kan nematoderna tillföra värdefull information. Då antal makrofauna-arter i Östersjön är lågt har bedömningar av ekosystemhälsa baserat på makrofauna mindre upplösning än bedömningar baserat på de mer mångfaldiga och abundanta nematod-samhället. Det finns dock hinder för DNA-streckkodning ska för att övervaka nematoder i Östersjön: 1. Bristande täckning av nematod-arter i nuvarande referensdatabaser. 2. Bristande kunskap om streckkodningsmetoders förmåga att kvantifiera nematod-samhället och återspegla samhällskompositionen i miljöerna som provtas. Och 3. Bristen på verktyg för att bedöma ekosystemhälsa och ekologiska status från data över nematod-samhället. NEMOte BARCODing har bidragit till att överkomma dessa brister och därigenom till att möjliggöra miljöövervakning av Östersjöns nematoder. I Arbetspaktet 1 förbättrade NEMOte BARCODing existerande referensdatabaser genom att ladda upp referenssekvenser av 18S och 28S rRNA-markörgenerna för 110 av Östersjöns nematod-arter. I Arbetspaket 2 utvärderades sekvenseringsmetoders lämplighet för miljöövervakning. 18S-streckkodning med TAReuk primerparen fungerade bäst av de testade metoderna, gav en god bild av nematod-samhället, och rekommenderas därav för nematod-övervakning i Östersjön. I Arbetspaket 3 har NEMOte BARCODing utvecklat ett verktyg för statusklassning med nematod-data, Nematod-BQI (BQInem), med utgångspunkt i det BQI som används inom svensk miljöövervakning. Andra potentiella verktyg för nematod-övervakning utforskades även och en karta ritades för Nematod-BQI:s framtida utvecklingen, med potentiell inkludering av fler meiofauna-grupper som ett alternativ. Slutligen så förslogs ett pilotprogram för streckkodningsbaserad nematod-övervakning, med rekommenderade metoder, provtagningsupplägg och status klassningsverktyg (BQInem). De frilevande nematoderna kan säga oss mycket om ekosystemens hälsa och arbetet inom NEMOte BARCODing har förhoppningsvis bidragit till att denna information förmedlas.
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| 13. |
- Shen, Dandan, et al.
(författare)
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Dispersal Modifies the Diversity and Composition of Active Bacterial Communities in Response to a Salinity Disturbance
- 2018
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Ingår i: Frontiers in Microbiology. - : FRONTIERS MEDIA SA. - 1664-302X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Dispersal can influence the response of bacterial communities to environmental changes and disturbances. However, the extent to which dispersal contributes to the community response in dependence of the character and strength of the disturbance remains unclear. Here, we conducted a transplant experiment using dialysis bags in which bacterioplankton originating from brackish and marine regions of the Saint Lawrence Estuary were reciprocally incubated in the two environments for 5 days. Dispersal treatments were set-up by subjecting half of the microcosms in each environment to an exchange of cells between the marine and brackish assemblages at a daily exchange rate of 6% (v/v), and the other half of microcosms were kept as the nondispersal treatments. Bacterial 16S rRNA sequencing was then used to examine the diversity and composition of the active communities. Alpha diversity of the marine communities that were exposed to the brackish environment was elevated greatly by dispersal, but declined in the absence of dispersal. This indicates that dispersal compensated the loss of diversity in the marine communities after a disturbance by introducing bacterial taxa that were able to thrive and coexist with the remaining community members under brackish conditions. On the contrary, alpha diversity of the brackish communities was not affected by dispersal in either environment. Furthermore, dispersal led to an increase in similarity between marine and brackish communities in both of the environments, with a greater similarity when the communities were incubated in the brackish environment. These results suggest that the higher initial diversity in the brackish than in the marine starting community made the resident community less susceptible to dispersing bacteria. Altogether, this study shows that dispersal modifies the diversity and composition of the active communities in response to a salinity disturbance, and enables the local adjustment of specific bacteria under brackish environmental conditions.
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| 14. |
- Wang, Kui, et al.
(författare)
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Efficient electro-demulsification of O/W emulsions and simultaneous oil removal enabled by a multiscale porous biocarbon electrode
- 2024
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 481
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Tidskriftsartikel (refereegranskat)abstract
- Emulsion wastewater contain substantial amounts of oil and various additives, which pose threats to the environment and human health. Demulsification is a crucial pretreatment stage for wastewater. This study aims to identify a novel electro-demulsification method with high oil removal efficiency and low energy consumption. Modified carbonized birch wood with a unique isotropic multiscale pore structure is used as a self-standing electrode to treat a toluene oil-in-water (O/W) emulsion. The electrode must have a highly porous structure to facilitate efficient water diffusion and oil adsorption. It must also have high electronic conductivity to expedite polarized molecular electrophoresis to realize penetration into the pores and, subsequently, demulsification. Guided by an applied electric field force, polarized O/W droplets are drawn toward the electrode, revealing electrical characteristics distinct from those of polarized organic molecules. This electric field force augments the capture and adhesion of droplets by the electric double layer at the electrode interface. Consequently, adsorbed droplets in close proximity to the electrode rupture due to the combined influence of the electric field force and the electrostatic effects stemming from the electrode's multiscale porous structure. This synergistic action enables demulsification to occur efficiently at low energy consumption levels. This study has revealed that electro-demulsification can effectively treat toluene emulsions stabilized by various surfactants and microemulsion containing toluene. Therefore, this electro-demulsification technology can be further developed for various types of water pollution.
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| 15. |
- Xie, Rongrong, et al.
(författare)
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Salt intrusion alters nitrogen cycling in tidal reaches as determined in field and laboratory investigations
- 2020
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 729
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Tidskriftsartikel (refereegranskat)abstract
- Salinization is a growing problem throughout the world and poses a threat especially to freshwater ecosystems. However, much remains to be learned about the mechanisms by which salinity impacts microbially mediated biogeochemical processes. Elevated nitrogen (N) concentrations in estuarine ecosystems have led to their eutrophication, but the relationship between N transformation and the functional genes involved in the response to saltwater intrusion is poorly understood. Here, using the Minjiang River, a tidal river in southeastern China as an easily accessible natural laboratory, we conducted a 2-year field survey to investigate N speciation during ebb and flood tides. Then, in a laboratory experiment we simulated the varying degrees of salt intrusion that occur in natural tidal reaches. The microcosm study allowed quantitative assessments of N transformation and functional gene responses. The field surveys showed that concentrations of NH4+ rose during flood tides, while the concentrations of NO3- and total N fluctuated. In the microcosms, NO3- concentrations decreased in response to salt pulses, due to simultaneous declines in the abundance of genes responsible for nitrification and increases in the abundance of those involved in dissimilatory nitrate reduction to ammonium (DNRA). The elevated salinity led to increased yields of NH4+, a response that correlated positively with the abundance of nrfA genes, involved in DNRA. Furthermore, an increase in salinity promoted N2O accumulation during the denitrification process. Altogether, our study suggests that saltwater intrusion leads to a decrease in nitrification while favoring N transformation via denitrification and DNRA and that N2O accumulation in the water is dependent on the strength of the salt pulse.
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| 16. |
- Zhou, Xin, et al.
(författare)
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3D-imaging of selective laser melting defects in a Co-Cr-Mo alloy by synchrotron radiation micro-CT
- 2015
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 98, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure defects set the mechanical property limits for solid Co-Cr-Mo alloy prepared by selective laser melting (SLM). Previous studies were mainly based on 2D SEM images and thus not able to provide information of the 3D morphologies of the complex defects. In this paper, the remaining porosities in Co-Cr-Mo alloy parts prepared by selective laser melting were presented in relation to the laser processing parameters. In order to understand the defect forming mechanism, accurate 3D images of defects inside SLM fabricated Co-Cr-Mo samples were provided by synchrotron radiation micro-CT imaging of 300 pm thick slices cut from a 10 mm cube. With 3D reconstructed images distinctive morphologies of SLM defects spanning across the consolidated powder layers were generated. The faults can be classified as single layer or multi-layers defects. The accidental single layer defects form as gaps between adjacent laser melt tracks or melt track discontinuousness caused by inherent fluid instability under various disturbances. The first formed single layer defect generates often a multi-layer defect spanning for 2-3 subsequent powder layers. By stabilizing the melt pool flow and by reducing the surface roughness through adjusting processing parameters it appears possible to reduce the defect concentrations.
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| 17. |
- Zhou, Xin, et al.
(författare)
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Balling phenomena in selective laser melted tungsten
- 2015
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 222, s. 33-42
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) of pure tungsten was carried out and the relevant consolidation issues were investigated. It was observed that balling of melted droplets at the laser focal points and entrapped cavities hindered the preparation of fully dense parts. An analysis of the balling mechanism reveals that SLM of tungsten is a process where melt spreading and solidification compete with each other and the final result is determined by intrinsic tungsten properties and the set laser processing parameters. Melted tungsten droplets wetted its own solid substrate at a low speed driven by capillary force, but solidified simultaneous at a high speed driven by the existing steep temperature gradient. Melted droplets solidified before spreading completely and kept their globular geometry instead of creating a flat layer. Tungsten bodies reaching a density of 14.8-15.2 g/cm(3) were prepared with an open irregular porosity and surface roughness. With a second laser scanning the balling W droplets were remelted at the building surface resulting in a much smoother appearance with less porosity and indicated a way to further improve relative density, near 16 g/cm(3) (82.9% theoretical density). Oxidation must be avoided, as any oxide contamination enriched preferably around the melt pool edge, changing the surface tension gradient and the thermocapillary convection thereby increasing balling.
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| 18. |
- Zhou, Xin, et al.
(författare)
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Textures formed in a CoCrMo alloy by selective laser melting
- 2015
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 631, s. 153-164
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Tidskriftsartikel (refereegranskat)abstract
- Unique crystal textures formed by selective laser melting of a CoCrMo alloy were characterized by electron backscattered diffraction. Preferred crystallographic orientations were found for individual grains in the solid alloy microstructure. Along the building or radial grain growth direction in the rapidly cooling melt pool the formed columnar grains were not purely < 001 > or < 111 >, as reported before, but a concurrence of < 001 > and < 011 >. Along the scanning direction, a (011) < 100 > texture was limited to the outmost surface whereas in the solid bulk the preferred orientation was a < 001 > fiber texture.
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