| 1. |
- Locke, Adam E, et al.
(författare)
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Genetic studies of body mass index yield new insights for obesity biology.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 197-401
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (P < 5 × 10(-8)), 56 of which are novel. Five loci demonstrate clear evidence of several independent association signals, and many loci have significant effects on other metabolic phenotypes. The 97 loci account for ∼2.7% of BMI variation, and genome-wide estimates suggest that common variation accounts for >20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
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| 2. |
- Shungin, Dmitry, et al.
(författare)
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New genetic loci link adipose and insulin biology to body fat distribution.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 187-378
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Tidskriftsartikel (refereegranskat)abstract
- Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms.
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| 3. |
- Ried, Janina S., et al.
(författare)
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A principal component meta-analysis on multiple anthropometric traits identifies novel loci for body shape
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Large consortia have revealed hundreds of genetic loci associated with anthropometric traits, one trait at a time. We examined whether genetic variants affect body shape as a composite phenotype that is represented by a combination of anthropometric traits. We developed an approach that calculates averaged PCs (AvPCs) representing body shape derived from six anthropometric traits (body mass index, height, weight, waist and hip circumference, waist-to-hip ratio). The first four AvPCs explain >99% of the variability, are heritable, and associate with cardiometabolic outcomes. We performed genome-wide association analyses for each body shape composite phenotype across 65 studies and meta-analysed summary statistics. We identify six novel loci: LEMD2 and CD47 for AvPC1, RPS6KA5/C14orf159 and GANAB for AvPC3, and ARL15 and ANP32 for AvPC4. Our findings highlight the value of using multiple traits to define complex phenotypes for discovery, which are not captured by single-trait analyses, and may shed light onto new pathways.
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| 4. |
- Surendran, Praveen, et al.
(författare)
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Trans-ancestry meta-analyses identify rare and common variants associated with blood pressure and hypertension
- 2016
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 48:10, s. 1151-1161
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Tidskriftsartikel (refereegranskat)abstract
- High blood pressure is a major risk factor for cardiovascular disease and premature death. However, there is limited knowledge on specific causal genes and pathways. To better understand the genetics of blood pressure, we genotyped 242,296 rare, low-frequency and common genetic variants in up to 192,763 individuals and used -1/4155,063 samples for independent replication. We identified 30 new blood pressure- or hypertension-associated genetic regions in the general population, including 3 rare missense variants in RBM47, COL21A1 and RRAS with larger effects (>1.5 mm Hg/allele) than common variants. Multiple rare nonsense and missense variant associations were found in A2ML1, and a low-frequency nonsense variant in ENPEP was identified. Our data extend the spectrum of allelic variation underlying blood pressure traits and hypertension, provide new insights into the pathophysiology of hypertension and indicate new targets for clinical intervention.
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| 5. |
- Eiler, Alexander, et al.
(författare)
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Unveiling Distribution Patterns of Freshwater Phytoplankton by a Next Generation Sequencing Based Approach
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:1, s. e53516-
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Tidskriftsartikel (refereegranskat)abstract
- The recognition and discrimination of phytoplankton species is one of the foundations of freshwater biodiversity research and environmental monitoring. This step is frequently a bottleneck in the analytical chain from sampling to data analysis and subsequent environmental status evaluation. Here we present phytoplankton diversity data from 49 lakes including three seasonal surveys assessed by next generation sequencing (NGS) of 16S ribosomal RNA chloroplast and cyanobacterial gene amplicons and also compare part of these datasets with identification based on morphology. Direct comparison of NGS to microscopic data from three time-series showed that NGS was able to capture the seasonality in phytoplankton succession as observed by microscopy. Still, the PCR-based approach was only semi-quantitative, and detailed NGS and microscopy taxa lists had only low taxonomic correspondence. This is probably due to, both, methodological constraints and current discrepancies in taxonomic frameworks. Discrepancies included Euglenophyta and Heterokonta that were scarce in the NGS but frequently detected by microscopy and Cyanobacteria that were in general more abundant and classified with high resolution by NGS. A deep-branching taxonomically unclassified cluster was frequently detected by NGS but could not be linked to any group identified by microscopy. NGS derived phytoplankton composition differed significantly among lakes with different trophic status, showing that our approach can resolve phytoplankton communities at a level relevant for ecosystem management. The high reproducibility and potential for standardization and parallelization makes our NGS approach an excellent candidate for simultaneous monitoring of prokaryotic and eukaryotic phytoplankton in inland waters.
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| 6. |
- Graham, Emily B., et al.
(författare)
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Microbes as Engines of Ecosystem Function : When Does Community Structure Enhance Predictions of Ecosystem Processes?
- 2016
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Microorganisms are vital in mediating the earth's biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: 'When do we need to understand microbial community structure to accurately predict function?' We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology.
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| 7. |
- Kritzberg, Emma S., et al.
(författare)
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Influence of dissolved organic matter source on lake bacterioplankton community structure and function : implications for seasonal dynamics of community structure.
- 2006
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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 56:3, s. 406-417
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that autochthonous (internally produced) organic carbon and allochthonous (externally produced) organic carbon are utilized by phylogenetically different bacterioplankton. We examined the relationship between the source of organic matter and the structure and function of lake bacterial communities. Differences and seasonal changes in bacterial community composition in two lakes differing in their source of organic matter were followed in relation to environmental variables. We also performed batch culture experiments with amendments of various organic substrates, namely fulvic acids, leachates from algae, and birch and maple leaves. Differences in bacterial community composition between the lakes, analysed by terminal restriction fragment length polymorphism, correlated with variables related to the relative loading of autochthonous and allochthonous carbon (water colour, dissolved organic carbon, nutrients, and pH). Seasonal changes correlated with temperature, chlorophyll and dissolved organic carbon in both lakes. The substrate amendments led to differences in both structure and function, i.e. production, respiration and growth yield, of the bacterial community. In conclusion, our results suggest that the source of organic matter influences community composition both within and among lakes and that there may be a coupling between the structure and function of the bacterial community.
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| 8. |
- Pearce, David A., et al.
(författare)
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First evidence for a bipolar distribution of dominant freshwater lake bacterioplankton
- 2007
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Ingår i: Antarctic Science. - 0954-1020 .- 1365-2079. ; 19:2, s. 245-252
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Tidskriftsartikel (refereegranskat)abstract
- As a result of the recent application of DNA based technology to the investigation of maritime Antarctic freshwater lakes, patterns have begun to emerge in the bacterioplankton communities that dominate these systems. In this study, the bacterioplankton communities of five Antarctic and five Arctic freshwater lakes were assessed and compared with existing data in the literature, to determine whether emerging patterns in Antarctic lakes also applied to Arctic systems. Such a bipolar comparison is particularly timely, given the current interest in biogeography, the global distribution of microorganisms and the controversy over the global ubiquity hypothesis. In addition, it has recently been discovered that commonly encountered bacterial sequences, often originating from uncultivated bacteria obtained on different continents, form coherent phylogenetic freshwater clusters. In this study we encountered both identical sequences and sequences with a high degree of similarity among the bacterioplankton in lake water from both poles. In addition, Arctic freshwater lakes appeared to be dominated by some of the same groups of bacterioplankton thought to be dominant in Antarctic lakes, the vast majority of which represented uncultivated groups.
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| 9. |
- Wallman, J. K., et al.
(författare)
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Validity of clinical psoriatic arthritis diagnoses made by rheumatologists in the Swedish National Patient Register
- 2023
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Ingår i: Scandinavian Journal of Rheumatology. - : Informa UK Limited. - 0300-9742 .- 1502-7732. ; 52:4, s. 374-384
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Tidskriftsartikel (refereegranskat)abstract
- Objectives : Knowledge of the correspondence between clinical ICD diagnoses and classification criteria fulfilment is crucial to interpret studies identifying cases via ICD codes. We assessed the degree to which patients registered with ICD-10 diagnoses of psoriatic arthritis (PsA) in the Swedish National Patient Register (NPR) fulfil established PsA classification criteria. Method Four hundred patients with at least one outpatient visit to one of five rheumatology or internal medicine departments (three university/two county departments across Sweden) in 2013-2015, with a main ICD-10 diagnosis of PsA (L40.5-M07.3), were randomly selected (80 cases/site). Through a structured medical record review, positive predictive values (PPVs) for fulfilment of the following classification criteria were assessed: CASPAR, Moll and Wright, Vasey and Espinoza, and modified ESSG criteria for PsA. A subset analysis regarding CASPAR fulfilment was also performed among cases with available rheumatoid factor and peripheral X-ray status (central CASPAR items; n = 227). Results Of the 400 patients with a main ICD-10 diagnosis of PsA, 343 (86%) fulfilled at least one of the four PsA classification criteria. PPVs for the different criteria were: CASPAR 69% (82% in the subset analysis), Moll and Wright 51%, Vasey and Espinoza 76%, and modified ESSG 64%. Overall, only 6.5% of the 400 PsA diagnoses were judged as clearly incorrect by the medical record reviewers. Conclusion The validity of rheumatologist-made, clinical ICD-10 diagnoses for PsA in the Swedish NPR is good, with PPVs of 69-82% for CASPAR fulfilment and 86% for meeting any established PsA classification criteria.
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| 10. |
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| 11. |
- Andersson, Martin G. I., et al.
(författare)
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Effects of sterilization on dissolved organic carbon (DOC) composition and bacterial utilization of DOC from lakes
- 2018
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 82:2, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- Sterilization of dissolved organic carbon (DOC) is an essential step in research on interactions between DOC and organisms, for example where the effect of different microbial communities on DOC is studied or vice versa. However, few studies have gone beyond acknowledging that sterilization of DOC influences its characteristics. Here, we aimed to provide further knowledge that enables scientists to better tailor their sterilization methods to their research question. To meet this aim, we conducted a sterilization experiment with DOC from 4 boreal lakes treated with 4 sterilization methods, i.e. 2 filtrations (0.2 µm, 0.1 µm) and 2 autoclaving approaches (single and double autoclaving with a single pH adjustment). Quantity and spectroscopic properties of DOC, before and after sterilization, were studied, and DOC was further tested as a substrate for bacterial growth. We found that the filtration methods better preserved the different DOC measures. In contrast, autoclaving caused major inconsistent shifts in both qualitative and quantitative measures of DOC, as well as an increase of the maximum abundance of bacteria in growth experiments. Nonetheless, there remains a trade-off between retaining the quality of DOC and achieving sterile conditions. Therefore, the sterilization method of choice should be guided by the scientific question at hand.
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| 12. |
- Andersson, Martin, et al.
(författare)
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The spatial structure of bacterial communities is influenced by historical environmental conditions
- 2014
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 95:5, s. 1134-1140
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Tidskriftsartikel (refereegranskat)abstract
- The spatial structure of ecological communities, including that of bacteria, is often influenced by species sorting by contemporary environmental conditions. Moreover, historical processes, i.e., ecological and evolutionary events that have occurred at some point in the past, such as dispersal limitation, drift, priority effects, or selection by past environmental conditions, can be important, but are generally investigated much less. Here, we conducted a field study using 16 rock pools, where we specifically compared the importance of past vs. contemporary environmental conditions for bacterial community structure by correlating present differences in bacterial community composition among pools to environmental conditions measured on the same day, as well as to those measured 2, 4, 6, and 8 d earlier. The results prove that selection by past environmental conditions exists, since we were able to show that bacterial communities are, to a greater extent, an imprint of past compared to contemporary environmental conditions. We suggest that this is the result of a combination of different mechanisms, including priority effects that cause rapid adaptation to new environmental conditions of taxa that have been initially selected by past environmental conditions, and slower rates of turnover in community composition compared to environmental conditions.
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| 13. |
- Beisner, Beatrix E., et al.
(författare)
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The role of environmental and spatial processes in structuring lake communities from bacteria to fish
- 2006
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 87:12, s. 2985-2991
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Tidskriftsartikel (refereegranskat)abstract
- We assessed the relative roles of local environmental conditions and dispersal on community structure in a landscape of lakes for the major trophic groups. We use taxonomic presence–absence and abundance data for bacteria, phytoplankton, zooplankton, and fish from 18 lakes in southern Quebec, Canada. The question of interest was whether communities composed of organisms with more limited dispersal abilities, because of size and life history (zooplankton and fish) would show a different effect of lake distribution than communities composed of good dispersers (bacteria and phytoplankton). We examine the variation in structure attributable to local environmental (i.e., lake chemical and physical variables) vs. dispersal predictors (i.e., overland and watercourse distances between lakes) using variation partitioning techniques. Overall, we show that less motile species (crustacean zooplankton and fish) are better predicted by spatial factors than by local environmental ones. Furthermore, we show that for zooplankton abundances, both overland and watercourse dispersal pathways are equally strong, though they may select for different components of the community, while for fish, only watercourses are relevant dispersal pathways. These results suggest that crustacean zooplankton and fish are more constrained by dispersal and therefore more likely to operate as a metacommunity than are bacteria and phytoplankton within this studied landscape.
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| 14. |
- Berga, Mercè, et al.
(författare)
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Combined effects of zooplankton grazing and dispersal on the diversity and assembly mechanisms of bacterial metacommunities
- 2015
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 17:7, s. 2275-2287
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Tidskriftsartikel (refereegranskat)abstract
- Effects of dispersal and the presence of predators on diversity, assembly and functioning of bacterial communities are well studied in isolation. In reality, however, dispersal and trophic interactions act simultaneously and can therefore have combined effects, which are poorly investigated. We performed an experiment with aquatic metacommunities consisting of three environmentally different patches and manipulated dispersal rates among them as well as the presence or absence of the keystone species Daphnia magna. Daphnia magnareduced both local and regional diversity, whereas dispersal increased local diversity but decreased beta-diversity having no net effect on regional diversity. Dispersal modified the assembly mechanisms of bacterial communities by increasing the degree of determinism. Additionally, the combination of the D. magna and dispersal increased the importance of deterministic processes, presumably because predator-tolerant taxa were spread in the metacommunity via dispersal. Moreover, the presence of D. magna affected community composition, increased community respiration rates but did not affect bacterial production or abundance, whereas dispersal slightly increased bacterial production. In conclusion, our study suggests that predation by a keystone species such as D. magna and dispersal additively influence bacterial diversity, assembly processes and ecosystem functioning.
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| 15. |
- Bergman, Ingrid, et al.
(författare)
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Ciliate Grazing on the Bloom-Forming Microalga Gonyostomum semen
- 2024
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Ingår i: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 87
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Tidskriftsartikel (refereegranskat)abstract
- The freshwater raphidophyte Gonyostomum semen forms extensive summer blooms in northern European humic lakes. The development of these blooms might be facilitated by a lack of natural top-down control, as few zooplankton species are able to prey on these large algal cells (up to 100 mu m) that expel trichocysts upon physical stress. In this study, we describe a small ciliate species (< 17 mu m) that preys on G. semen by damaging the cell membrane until cytoplasm and organelles spill out. Sequencing of clonal cultures of the ciliate tentatively identified it as the prostomatid species Urotricha pseudofurcata. Grazing experiments illustrated that feeding by U. cf. pseudofurcata can significantly reduce cell concentrations of the microalga. However, differences in cell size and growth rate between two investigated ciliate strains resulted in noticeably different grazing pressure. Environmental sequencing data from five different lakes supported potential interactions between the two species. Urotricha cf. pseudofurcata might, thus, play an important role in aquatic ecosystems that are regularly dominated by G. semen, reducing the abundance of this bloom-forming microalga and enabling transfer of organic carbon to higher trophic levels.
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| 16. |
- Bergström, Ann-Kristin, et al.
(författare)
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Composition and dispersal of riverine and lake phytoplankton communities in connected systems with different hydraulic retention times
- 2008
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 53:12, s. 2520-2529
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Tidskriftsartikel (refereegranskat)abstract
- 1. Lake phytoplankton community structure may be influenced by both internal factors (predation, competition, resource constraints) and external ones, such as dispersal of materials and cells between connected habitats. However, little is known about the importance of cell dispersal for phytoplankton community structure in lakes. 2. We investigated the abundance and dispersal of phytoplankton cells between connected rivers and lakes, and analysed whether similarities in phytoplankton community composition between rivers and lakes were primarily related to cell import rates or to characteristics of the local habitat. We focused on lakes along a gradient of theoretical water retention times (TWRT). Two data sets from Swedish lakes were used; a seasonal study of two connected boreal forest lakes, differing in TWRT, and a multi-lake study of 13 lakes with a continuous range of TWRTs. 3. Phytoplankton cells were transported and dispersed in all investigated rivers. In the seasonal study, cell import rates and similarities in phytoplankton community composition between the lake and its inlet(s) were much higher in the lake with a shorter TWRT. Phytoplankton community structure in different habitats was associated with total organic carbon (TOC). This indicates that local habitat characteristics may be important in determining lake phytoplankton community composition, even in the presence of substantial cell import. 4. The multi-lake study also showed a negative relationship between TWRT and similarities in phytoplankton community composition between inlets and lakes. Moreover, similarity in community structure was related to both cell import rates from inlet to lake and differences in habitat characteristics between inlet and lake. However, the variable most strongly correlated with community structure was TOC, indicating that species sorting rather than a mass effect was the most important mechanism underlying the correlation between community structure and retention time. 5. Overall, our data suggest that local habitat characteristics may play a key role in determining community similarity in this set of lakes covering a large range of habitat connectedness. Due to the strong co-variations between cell dispersal and TOC, it was hard to unequivocally disentangle the different mechanisms; hence, there is a need for further studies of the role of dispersal for phytoplankton community structures
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| 17. |
- Besemer, Katharina, et al.
(författare)
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Unraveling assembly of stream biofilm communities
- 2012
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Ingår i: The ISME Journal: multidisciplinary journal of microbial ecology. - : Springer Science and Business Media LLC. - 1751-7362. ; 6:8, s. 1459-1468
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Tidskriftsartikel (refereegranskat)abstract
- Microbial biofilms assemble from cells that attach to a surface, where they develop into matrix-enclosed communities. Mechanistic insights into community assembly are crucial to better understand the functioning of natural biofilms, which drive key ecosystem processes in numerous aquatic habitats. We studied the role of the suspended microbial community as the source of the biofilm community in three streams using terminal-restriction fragment length polymorphism and 454 pyrosequencing of the 16S ribosomal RNA (rRNA) and the 16S rRNA gene (as a measure for the active and the bulk community, respectively). Diversity was consistently lower in the biofilm communities than in the suspended stream water communities. We propose that the higher diversity in the suspended communities is supported by continuous inflow from various sources within the catchment. Community composition clearly differed between biofilms and suspended communities, whereas biofilm communities were similar in all three streams. This suggests that biofilm assembly did not simply reflect differences in the source communities, but that certain microbial groups from the source community proliferate in the biofilm. We compared the biofilm communities with random samples of the respective community suspended in the stream water. This analysis confirmed that stochastic dispersal from the source community was unlikely to shape the observed community composition of the biofilms, in support of species sorting as a major biofilm assembly mechanism. Bulk and active populations generated comparable patterns of community composition in the biofilms and the suspended communities, which suggests similar assembly controls on these populations.
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| 18. |
- Comte, Jerome, et al.
(författare)
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Contribution of different bacterial dispersal sources to lakes : Population and community effects in different seasons
- 2017
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Ingår i: Environmental Microbiology. - : Wiley-Blackwell. - 1462-2912 .- 1462-2920. ; 19:6, s. 2391-2404
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Tidskriftsartikel (refereegranskat)abstract
- The diversity and composition of lake bacterial communities are driven by the interplay between local contemporary environmental conditions and dispersal of cells from the surroundings, i.e. the metacommunity. Still, a conceptual understanding of the relative importance of the two types of factors is lacking. For instance, it is unknown which sources of dispersal are most important and under which circumstances. Here, we investigated the seasonal variation in the importance of dispersal from different sources (mixing, precipitation, surface runoff and sediment resuspension) for lake bacterioplankton community and population dynamics. For that purpose, two small forest lakes and their dispersal sources were sampled over a period of 10 months. The influence of dispersal on communities and populations was determined by 454 sequencing of the 16S rRNA gene and SourceTracker analysis. On the community level direct effects of dispersal were questionable from all sources. Instead we found that the community of the preceding sampling occasion, representing growth of resident bacteria, was of great importance. On the population level, however, dispersal of individual taxa from the inlet could be occasionally important even under low water flow. The effect of sediment resuspension and precipitation appeared small.
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| 19. |
- Comte, Jérôme, et al.
(författare)
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Contribution of different dispersal sources to the metabolic response of lake bacterioplankton following a salinity change
- 2017
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 19:1, s. 251-260
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Tidskriftsartikel (refereegranskat)abstract
- Dispersal can modify how bacterial community composition (BCC) changes in response to environmental perturbations, yet knowledge about the functional consequences of dispersal is limited. Here we hypothesize that changes in bacterial community production in response to a salinity disturbance depend on the possibility to recruit cells from different dispersal sources. To investigate this, we conducted an in situ mesocosm experiment where bacterial communities of an oligotrophic lake were exposed to different salinities (0, 18, 36 psu) for two weeks and subjected to dispersal of cells originating from sediments, air (mesocosms open to air deposition), both or none. BCC was determined using 454 pyrosequencing of the 16S rRNA gene and bacterial production was measured by 3H leucine uptake. Bacterial production differed significantly among salinity treatments and dispersal treatments, being highest at high salinity. These changes were associated with changes in BCC and it was found that the identity of the main functional contributors differed at different salinities. Our results further showed that after a salinity perturbation, the response of bacterial communities depended on the recruitment of taxa, including marine representatives (e.g. Alphaproteobacteria Loktanella, Erythrobacter and the Gammaproteobacterium Rheiheimera) from dispersal sources, in which atmospheric deposition appeared to play a major role.
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| 20. |
- Exarchou, Sofia, et al.
(författare)
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The National Prevalence of Clinically Diagnosed Psoriatic Arthritis in Sweden in 2017
- 2023
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Ingår i: Journal of Rheumatology. - : The Journal of Rheumatology. - 0315-162X .- 1499-2752. ; 50:6, s. 781-788
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Tidskriftsartikel (refereegranskat)abstract
- Objective. Psoriatic arthritis (PsA) prevalence estimates vary across studies; studies based on national data are few. We aimed to estimate the prevalence of clinically diagnosed PsA in Sweden in 2017, overall and stratified by sex, age, education, and geography, and to quantify disease-modifying antirheumatic drug (DMARD) use among those in contact with specialized rheumatology care between 2015 and 2017.Methods. Individuals who were 18 to 79 years of age, alive and residing in Sweden on December 31, 2017, and had a prior PsA diagnosis were identified from the National Patient Register (NPR) and/or the Swedish Rheumatology Quality Register (SRQ). PsA prevalence was estimated according to a base case (BC) defini-tion (ie, & GE; 1 main PsA International Classification of Diseases code from rheumatology or internal medicine departments in the NPR or a PsA diagnosis in the SRQ), according to 4 sensitivity analysis definitions, and for those seen in specialized rheumatology care between 2015 and 2017. In the latter group, DMARD use during 2017 was also assessed. Data for stratifications were retrieved from national registers.Results. The crude national prevalence of PsA for adults, aged 18 to 79 years, was estimated at 0.39%, according to the BC definition; 0.34% after accounting for diagnostic misclassification; and 0.32% to 0.50% across all sensitivity analyses. The prevalence was lower in males and in those with a higher level of education. The prevalence for those seen in specialized rheumatology care between 2015 and 2017 was estimated at 0.24%. During 2017, 32% of patients in this population received biologic or targeted synthetic DMARDs, and 41% received conventional synthetic DMARDs only.Conclusion. The prevalence of clinically diagnosed PsA in adults, aged 18 to 79 years, in Sweden in 2017 was around 0.35%. Among PsA cases in recent contact with specialized rheumatology care, almost three-fourths received DMARD therapy in 2017.
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| 21. |
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| 22. |
- Hessen, Dag O., et al.
(författare)
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Production and food web interactions of Arctic freshwater plankton and responses to increased DOC
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 159:3, s. 289-307
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Tidskriftsartikel (refereegranskat)abstract
- A gradient of dissolved organic carbon (DOC) was added to enclosures in a high Arctic lake (Svalbard, 79 N). The aim was to simulate the effect of increased concentrations of DOC that will be a predicted effect of increased temperature and precipitation. The study aimed to provide information on the overall effects of such increased levels of DOC on the pelagic food-web, as well as the increased attenuation of UV-radiation (UV-R) caused by increased DOC. The biomass development of phytoplankton, heterotrophic bacteria and ciliates from 15. July (shortly after ice-off) to 8. August revealed a consistent pattern across all enclosures. Initial phytoplankton biomass decreased from maxima around 600g Cl-1 towards 50g Cl-1 by the end of July. Similarly, ciliate biomass decreased from ~100 to 5g Cl-1, while heterotrophic bacteria decreased from initially 280 g Cl-1 to biomasses near 100 g Cl-1. Over the same period, zooplankton biomass (almost a monoculture of Daphnia tenebrosa) increased from <40 to some 170g Cl-1. These patterns were reflected also in decreasing absolute production of bacteria and phytoplankton, while production:biomass ratio remained fairly constant. In general, the study demonstrated a very dynamic system over the brief ice-free season, where Daphnia grazing had a strong impact on the unicellular biota. Additions of DOC initially stimulated planktonic production, yet this effect was soon overruled by Daphnia grazing. This stimulating effect could be a result both of increased UV-R attenuation and some growth stimulating effect. Since no corresponding stimulating effect was observed in the bag shielded with Mylar filter to screen off UV-B, the latter cause seems most likely.
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| 23. |
- Hillebrand, Helmut, et al.
(författare)
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Decomposing multiple dimensions of stability in global change experiments
- 2018
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 21:1, s. 21-30
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Tidskriftsartikel (refereegranskat)abstract
- Ecological stability is the central framework to understand an ecosystem's ability to absorb or recover from environmental change. Recent modelling and conceptual work suggests that stability is a multidimensional construct comprising different response aspects. Using two freshwater mesocosm experiments as case studies, we show how the response to single perturbations can be decomposed in different stability aspects (resistance, resilience, recovery, temporal stability) for both ecosystem functions and community composition. We find that extended community recovery is tightly connected to a nearly complete recovery of the function (biomass production), whereas systems with incomplete recovery of the species composition ranged widely in their biomass compared to controls. Moreover, recovery was most complete when either resistance or resilience was high, the latter associated with low temporal stability around the recovery trend. In summary, no single aspect of stability was sufficient to reflect the overall stability of the system.
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| 24. |
- Hunley, Keith, et al.
(författare)
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Genetic and Linguistic Coevolution in Northern Island Melanesia
- 2008
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Ingår i: PLOS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have detailed a remarkable degree of genetic and linguistic diversity in Northern Island Melanesia. Here we utilize that diversity to examine two models of genetic and linguistic coevolution. The first model predicts that genetic and linguistic correspondences formed following population splits and isolation at the time of early range expansions into the region. The second is analogous to the genetic model of isolation by distance, and it predicts that genetic and linguistic correspondences formed through continuing genetic and linguistic exchange between neighboring populations. We tested the predictions of the two models by comparing observed and simulated patterns of genetic variation, genetic and linguistic trees, and matrices of genetic, linguistic, and geographic distances. The data consist of 751 autosomal microsatellites and 108 structural linguistic features collected from 33 Northern Island Melanesian populations. The results of the tests indicate that linguistic and genetic exchange have erased any evidence of a splitting and isolation process that might have occurred early in the settlement history of the region. The correlation patterns are also inconsistent with the predictions of the isolation by distance coevolutionary process in the larger Northern Island Melanesian region, but there is strong evidence for the process in the rugged interior of the largest island in the region (New Britain). There we found some of the strongest recorded correlations between genetic, linguistic, and geographic distances. We also found that, throughout the region, linguistic features have generally been less likely to diffuse across population boundaries than genes. The results from our study, based on exceptionally fine-grained data, show that local genetic and linguistic exchange are likely to obscure evidence of the early history of a region, and that language barriers do not particularly hinder genetic exchange. In contrast, global patterns may emphasize more ancient demographic events, including population splits associated with the early colonization of major world regions.
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| 25. |
- Hunley, Keith, et al.
(författare)
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Inferring Prehistory from Genetic, Linguistic, and Geographic Variation
- 2007
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Ingår i: Population Genetics, Linguistics, and Culture History in the Southwest Pacific. - : Oxford University Press. ; , s. 141-155
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter investigates the fit of genetic, phenotypic, and linguistic data to two well-known models of population history. The first of these models, termed the population fissions model, emphasizes population splitting, isolation, and independent evolution. It predicts that genetic and linguistic data will be perfectly tree-like. The second model, termed isolation by distance, emphasizes genetic exchange among geographically proximate populations. It predicts a monotonic decline in genetic similarity with increasing geographic distance. While these models are overly simplistic, deviations from them were expected to provide important insights into the population history of northern Island Melanesia. The chapter finds scant support for either model because the prehistory of the region has been so complex. Nonetheless, the genetic and linguistic data are consistent with an early radiation of proto-Papuan speakers into the region followed by a much later migration of Austronesian speaking peoples. While these groups subsequently experienced substantial genetic and cultural exchange, this exchange has been insufficient to erase this history of separate migrations.
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| 26. |
- Jezberova, Jitka, et al.
(författare)
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Ubiquity of Polynucleobacter necessarius ssp asymbioticus in lentic freshwater habitats of a heterogenous 2000 km2 area
- 2010
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 12:3, s. 658-669
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Tidskriftsartikel (refereegranskat)abstract
- We present a survey on the distribution and habitat range of Polynucleobacter necessarius ssp. asymbioticus (PnecC), a numerically and functionally important taxon in the plankton of freshwater systems. We systematically sampled stagnant freshwater habitats in a heterogeneous 2000 km2 area, together with ecologically different habitats outside this area. In total, 137 lakes, ponds and puddles were investigated, which represent an enormous diversity of habitats differing, e.g. in depth (< 10 cm - 171 m) and pH (3.9-8.5). PnecC bacteria were detected by cultivation-independent methods in all investigated habitats, and their presence was confirmed by cultivation of strains from selected habitats representing the whole studied ecological range. The determined relative abundance of the subspecies ranged from values close to the detection limit of FISH (0.2%) to 67% (average 14.5%), and the highest observed absolute abundance was 5.3 x 106 cells ml-1. Statistical analyses revealed that the abundance of PnecC bacteria was partially controlled by factors linked to concentrations of humic substances, which support the hypothesis that these bacteria utilize photodegradation products of humic substances. Based on the revealed statistical relationships, an average relative abundance of this subspecies of 20% in global freshwater habitats was extrapolated. Our study provides important implications for the current debate on ubiquity and biogeography in microorganisms.
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| 27. |
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| 28. |
- Langenheder, Silke, et al.
(författare)
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Factors influencing aquatic and terrestrial bacterial community assembly
- 2019
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Ingår i: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 11:3, s. 306-315
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Forskningsöversikt (refereegranskat)abstract
- During recent years, many studies have shown that different processes including drift, environmental selection and dispersal can be important for the assembly of bacterial communities in aquatic and terrestrial ecosystems. However, we lack a conceptual overview about the ecological context and factors that influence the relative importance of the different assembly mechanisms and determine their dynamics in time and space. Focusing on free-living, i.e., nonhost associated, bacterial communities, this minireview, therefore, summarizes and conceptualizes findings from empirical studies about how (i) environmental factors, such as environmental heterogeneity, disturbances, productivity and trophic interactions; (ii) connectivity and dispersal rates (iii) spatial scale, (iv) community properties and traits and (v) the use of taxonomic/phylogenetic or functional metrics influence the relative importance of different community assembly processes. We find that there is to-date little consistency among studies and suggest that future studies should now address how (i)-(v) differ between habitats and organisms and how this, in turn, influences the temporal and spatial-scale dependency of community assembly processes in microorganisms.
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| 29. |
- Langenheder, Silke, et al.
(författare)
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Growth dynamics within bacterial communities in riverine and estuarine batch cultures
- 2004
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 37, s. 137-148
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Tidskriftsartikel (refereegranskat)abstract
- We investigated temporal changes in community composition of bacteria growing on riverine dissolved organic carbon. Batch cultures were adjusted to riverine or estuarine salinity levels and inoculated with bacteria from these 2 environments to test whether growth patterns of bacterial taxa are influenced by salinity and/or the source of the inoculum. Changes in bacterial community composition at different stages of the growth phase were studied by 16S rDNA denaturing gradient gel electrophoresis (DGGE). Furthermore, the growth dynamics of 7 bacteria previously isolated from the estuary were followed by quantitative DNA-DNA hybridization. Growth dynamics within bacterial communities were significantly influenced by the source of the inoculum but not by salinity, suggesting that slight changes in salinity, to which riverine bacteria are exposed when discharged into the Northern Baltic Sea, are not a major regulating factor of community dynamics. Additionally, our results indicated only minor differences in the appearance and growth of bacteria when examined by quantitative DNA-DNA hybridization, whereas DGGE banding patterns suggested that there were fast- and slow-growing types of bacteria.
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| 30. |
- Langenheder, Silke, et al.
(författare)
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Remnants of marine bacterial communities can be retrieved from deep sediments in lakes of marine origin
- 2016
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Ingår i: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 8:4, s. 479-485
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Tidskriftsartikel (refereegranskat)abstract
- Some bacteria can be preserved over time in deep sediments where they persist either in dormant or slow-growing vegetative stages. Here, we hypothesized that such cells can be revived when exposed to environmental conditions similar to those before they were buried in the sediments. To test this hypothesis, we collected bacteria from sediment samples of different ages (140–8500 calibrated years before present, cal BP) from three lakes that differed in the timing of their physical isolation from the Baltic Sea following postglacial uplift. After these bacterial communities were grown in sterile water from the Baltic Sea, we determined the proportion of 16S rRNA sequence reads associated with marine habitats by extracting the environment descriptive terms of homologous sequences retrieved from public databases. We found that the proportion of reads associated with marine descriptive term was significantly higher in cultures inoculated with sediment layers formed under Baltic conditions and where salinities were expected to be similar to current levels. Moreover, a similar pattern was found in the original sediment layers. Our study, therefore, suggests that remnants of marine bacterial communities can be preserved in sediments over thousands of years and can be revived from deep sediments in lakes of marine origin.
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| 31. |
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| 32. |
- Langenheder, Silke, et al.
(författare)
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Weak coupling between community composition and functioning of aquatic bacteria
- 2005
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 50:3, s. 957-967
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Tidskriftsartikel (refereegranskat)abstract
- We performed a batch culture experiment with a factorial design in which sterile water from four lakes and bacterial assemblages (size-fractionated lake water) from the same lakes were set up in all possible combinations. The functional performance (biomass yield, respiration, growth rates, and growth efficiency) of bacterial communities growing in the cultures depended primarily on the type of the medium and to a much lesser extent on the origin of the bacterial assemblage. Functional changes were only partly paralleled by changes in community composition, as indicated by terminal restriction fragment length polymorphism analysis. Similar bacterial communities developed in different cultures as a result of receiving either the same medium or the same inoculum, indicating that bacterial communities are comprised of populations of generalists that can grow under most conditions as well as populations with the life strategy of specialists. However, bacteria originating from a slightly acidic polyhumic lake failed to grow, grew unsteadily, or exhibited an extended lag phase when exposed to media originating from other lakes, indicating that the bacterial community in the polyhumic lake was not able to adapt rapidly to changes in environmental conditions.
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| 33. |
- Lebret, Karen, et al.
(författare)
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High abundances of the nuisance raphidophyte Gonyostomum semen in brown water lakes are associated with high concentrations of iron
- 2018
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Algal blooms occur frequently in lakes and oceans and the causes and consequences of those are often studied. In this study, we focus on a less well known type of algal bloom by the freshwater raphidophyte Gonyostomum semen. This species' abundance and occurrence is increasing, especially in brown water lakes, the most abundant lake type in the boreal zone. The aim of the study was to investigate which environmental factors are associated with G. semen by statistical evaluation of field data of 95 Swedish lakes over five years. Although we found G. semen to be associated with dark waters it was, contrary to our expectations, mainly high concentrations of iron, and only to a lesser extent high TOC (total organic carbon) concentrations, that were associated with blooms of G. semen. In addition, high phosphorus concentrations and low pH also appear to facilitate G. semen blooms. We suggest that browning of lakes caused by increased iron concentrations may decrease net heterotrophy by fostering heavy algal blooms, i.e. the opposite to commonly assumed effects of increased DOM (dissolved organic matter).
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| 34. |
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| 35. |
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Lindström, Eva S, et al.
(författare)
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Influence of inlet bacteria on bacterioplankton assemblage composition in lakes of different hydraulic retention time
- 2004
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Ingår i: Limnol. Oceanogr.. ; 49:1, s. 125–136-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of inlet bacteria on the assemblage composition of bacterioplankton was investigated in two Swedish forest lakes of different hydraulic retention time. Assemblage composition of the bacteria in lakes and running waters was determined by denaturing gradient gel electrophoresis (DGGE) and sequencing of polymerase chain reaction (PCR)-amplified 16S rDNA. The amount of bacterial cells imported via the inlets in relation to bacterioplankton cells produced in the epilimnion of the lakes was also determined. In the lake with short retention time (theoretical hydraulic retention time of 0.3 yr) the lake bacterioplankton assemblage largely resembled the riverine assemblages, although the extent of similarity varied among inlets, depending on water flow. In the lake with long retention time (theoretical hydraulic retention time of 10 yr) the bacterioplankton assemblage in the lake had low similarity to the inlet assemblages. The degree of similarity between inlets and lakes was well correlated to the amount of imported cells. Thus, our data suggest that import of inlet bacteria could have a large effect on the composition of lake bacterioplankton assemblages and that hydrological factors determined the magnitude of this effect. Since short hydraulic retention times are very common in lakes in the boreal zone, input of allochthonous bacteria can be one major factor influencing bacterioplankton assemblage composition in boreal lakes.
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| 44. |
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| 45. |
- Lindström, Eva S., et al.
(författare)
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Local and regional factors influencing bacterial community assembly
- 2012
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Ingår i: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 4:1, s. 1-9
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Forskningsöversikt (refereegranskat)abstract
- The classical view states that microbial biogeography is not affected by dispersal barriers or historical events, but only influenced by the local contemporary habitat conditions (species sorting). This has been challenged during recent years by studies suggesting that also regional factors such as mass effect, dispersal limitation and neutral assembly are important for the composition of local bacterial communities. Here we summarize results from biogeography studies in different environments, i.e. in marine, freshwater and soil as well in human hosts. Species sorting appears to be the most important mechanism. However, this result might be biased since this is the mechanism that is easiest to measure, detect and interpret. Hence, the importance of regional factors may have been underestimated. Moreover, our survey indicates that different assembly mechanisms might be important for different parts of the total community, differing, for example, between generalists and specialists, and between taxa of different dispersal ability and motility. We conclude that there is a clear need for experimental studies, first, to clearly separate regional and local factors in order to study their relative importance, and second, to test whether there are differences in assembly mechanisms depending on different taxonomic or functional groups.
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| 46. |
- Lindström, Eva S., et al.
(författare)
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Progress and perspectives in aquatic microbial ecology : highlights of the SAME 14, Uppsala, Sweden, 2015
- 2017
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 80:1, s. 101-103
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Tidskriftsartikel (refereegranskat)abstract
- The presentations and discussion during the Symposium of Aquatic Microbial Ecology (SAME) in Uppsala, Sweden, in August 2015 highlighted new directions and challenges in the study of aquatic microbial communities. In this virtual Special Issue, plenary speakers and meeting awardees explore these challenges. The contributions cover a wide range of topics from the use of molecular analyses of microbial communities to cultivation and stoichiometric analyses. The virtual Special also includes theoretical developments on the concept of rarity to community assembly. A common theme for the Special is, however, the importance of a combination of different approaches in order to deepen our understanding of the ecology of microbial communities.
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| 47. |
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| 48. |
- Lindström, Eva S, et al.
(författare)
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Response of a member of the Verrucomicrobia, among the dominating bacteria in a hypolimnion, to increased phosphorus availability
- 2004
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 1464-3774. ; 26:2, s. 241-246
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Tidskriftsartikel (refereegranskat)abstract
- In Lake Siggeforasjön, Sweden, a member of the Verrucomicrobia was found to be a large constituent of the bacteria in the hypolimnion, but not in the epilimnion. In a mesocosm experiment in the epilimnion, this particular Verrucomicrobia was favoured by increased phosphorus availability. The community composition of bacterioplankton was investigated by denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rDNA.During the last decade, molecular studies of the taxonomic composition of bacterioplankton communities in lakes and oceans have led to the discovery of a large number of ‘new’ bacteria (Giovannoni and Rappé, 2000; Glöckner et al., 2000). The occurrence of different bacterial taxa in the plankton community varies in time and space, and thus these taxa are likely to play different roles in the ecosystems. Recent results have indicated that the number of bacterioplankton taxa that still remain to be discovered is limited (Hagström et al., 2002; Zwart et al., 2002). However, so far, very little is known about the ecology of individual bacterioplankton species, for instance about which environmental factors can impact their abundance (Zwart et al., 2002).The purpose of this study was to investigate the factors that affect the composition of bacterioplankton at different depths in lakes. We compared the bacterioplankton communities in the epilimnion and the hypolimnion of a lake, and performed a 4 day mesocosm experiment where phosphorus (P) availability was manipulated to test whether it contributed to differences in bacterioplankton community composition between the layers.The community composition of bacterioplankton was investigated by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA, as described previously (Lindström, 1998). DGGE is a method that can be used to obtain an overview of the composition of the most dominant bacterioplankton taxa [e.g. (Torsvik et al., 1998)]. The pairwise similarity of the gel patterns of the samples was calculated using Sørensen’s index (Sørensen, 1948).Samples were taken from the temperate dimictic Lake Siggeforasjön, located near Uppsala, in the southern part of central Sweden (59°N, 17°E). This lake is oligo-mesotrophic and moderately humic (Table I). The community composition of the bacterioplankton in the lake has been investigated previously (Lindström, 1998, 2000; Lindström and Leskinen, 2002).
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| 49. |
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| 50. |
- Lindström, Eva S.
(författare)
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Temporal and spatial variation in the community composition of lake bacterioplankton
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bacterioplankton are among the smallest and most abundant organisms in lake ecosystems. Due to the lack of relevant methods, the taxonomic composition of bacterioplankton has been studied less thoroughly than that of larger organisms. The work described in this thesis has focused on analyzing temporal and spatial variations in bacterioplankton community composition, especially in relation to environmentalparameters. The community composition was determined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified (polymerase chain reaction) 16S rDNA (16S rRNA encoding DNA).Temporal changes within a bacterioplankton community in a mesotrophic brownwater lake were observed over a two-year period. These changes appeared to occur slowly and gradually, without any apparent coupling to season. The inflow of water from the drainage area was one possible factor causing the observed changes. The bacterioplankton community composition at different depths in two stratified lakes was investigated in a combined field survey and field experiment. The results suggest that differences between strata in the amount of dissolved oxygen, the availability of phosphorus, and temperature were important factors contributing to differences in community composition.Differences in community composition were also detected between five lakes differing in trophic status and humic content. The results indicated that the amount of potential grazers (mixotrophic flagellates and microzooplankton) present in the lakes had an impact on bacterioplankton community structure. The abundance of these organisms appeared to be coupled to the trophic status of the systems, indicating that trophic status at least indirectly influenced the composition of the bacterioplankton communities.Differences in bacterioplankton community composition were also found in five lakes of similar trophic status but different humic content. In these lakes grazers again appeared to be important, as did the size of both the lakes and their drainage areas. The coupling to humic content was less evident.In summary, many physical, chemical, and biological factors within the pelagic environments as well as in surrounding ecosystems appear to influence the taxonomic structure of bacterioplankton communities, which was found to vary in time and space.
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