| 1. |
- Liu, Haoyu, et al.
(författare)
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Distinct B cell subsets in Peyer's patches convey probiotic effects by Limosilactobacillus reuteri
- 2021
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Ingår i: Microbiome. - : Springer Nature. - 2049-2618. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Background: Intestinal Peyer's patches (PPs) form unique niches for bacteria-immune cell interactions that direct host immunity and shape the microbiome. Here we investigate how peroral administration of probiotic bacterium Limosilactobacillus reuteri R2LC affects B lymphocytes and IgA induction in the PPs, as well as the downstream consequences on intestinal microbiota and susceptibility to inflammation.Results: The B cells of PPs were separated by size to circumvent activation-dependent cell identification biases due to dynamic expression of markers, which resulted in two phenotypically, transcriptionally, and spatially distinct subsets: small IgD(+)/GL7(-)/S1PR1(+)/Bcl6, CCR6-expressing pre-germinal center (GC)-like B cells with innate-like functions located subepithelially, and large GL7(+)/S1PR1(-)/Ki67(+)/Bcl6, CD69-expressing B cells with strong metabolic activity found in the GC. Peroral L. reuteri administration expanded both B cell subsets and enhanced the innate-like properties of pre-GC-like B cells while retaining them in the sub-epithelial compartment by increased sphingosine-1-phosphate/S1PR1 signaling. Furthermore, L. reuteri promoted GC-like B cell differentiation, which involved expansion of the GC area and autocrine TGF beta-1 activation. Consequently, PD-1-T follicular helper cell-dependent IgA induction and production was increased by L. reuteri, which shifted the intestinal microbiome and protected against dextran-sulfate-sodium induced colitis and dysbiosis.Conclusions: The Peyer's patches sense, enhance and transmit probiotic signals by increasing the numbers and effector functions of distinct B cell subsets, resulting in increased IgA production, altered intestinal microbiota, and protection against inflammation.
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| 2. |
- Abrahamsson, Katarina, 1957, et al.
(författare)
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Variations of biochemical parameters along a transect in the Southern Ocean, with special emphasis on volatile halogenated organic compounds
- 2004
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Ingår i: Deep-sea research. Part II, Topical studies in oceanography. - : Elsevier BV. - 0967-0645. ; 51:22-24, s. 2745-2756
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Tidskriftsartikel (refereegranskat)abstract
- A number of parameters of biogeochemical interest were monitored along a north-southerly transect (S 43-S 63degrees) in the Atlantic Sector of the Southern Ocean from the 8th to the 20th of December 1997. Changes in total dissolved inorganic carbon (C-T) and total alkalinity (A(T)) were mostly dependent on temperature and salinity until the ice edge was reached. After this point only a weak correlation was seen between these. Highest mean values of C-T and A(T) were observed in the Winter Ice Edge (WIE) (2195 and 2319 mumol kg(-1), respectively). Lowest mean AT (2277 mumol kg(-1)) was observed in the Sub-Antarctic Front (SAF), whereas lowest mean CT concentration (2068 mumol kg(-1)) was associated with the Sub-Tropical Front (STF). The pH in situ varied between 8.060 and 8.156 where the highest values were observed in the southern part of the Antarctic Polar Front (APF) and in the Summer Ice Edge (SIE) Region. These peaks were associated with areas of high chlorophyll a (chl a) and tribromomethane values. In the other areas the pH in situ was mainly dependent on hydrography. Bacterial abundance decreased more than one order of magnitude when going from north to south. The decrease appeared to be strongly related to water temperature and there were no elevated abundances at frontal zones. Microphytoplankton dominated in the SAF and APF, whereas the nano- and picoplankton dominated outside these regions. Volatile halogenated compounds were found to vary both with regions, and with daylight. For the iodinated compounds, the highest concentrations were found north of the STF. Brominated hydrocarbons had high concentrations in the STF, but elevated concentrations were also found in the APF and SIE regions. No obvious correlation could be found between the occurrence of individual halocarbons and chl a. On some occasions trichloroethene and tribromomethane related to the presence of nano- and microplankton, respectively.
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| 3. |
- Ahmed Osman, Omneya, et al.
(författare)
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Interactions of Freshwater Cyanobacteria with Bacterial Antagonists
- 2017
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 83:7
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Tidskriftsartikel (refereegranskat)abstract
- Cyanobacterial and algal mass development, or blooms, have severe effects on freshwater and marine systems around the world. Many of these phototrophs produce a variety of potent toxins, contribute to oxygen depletion, and affect water quality in several ways. Coexisting antagonists, such as cyanolytic bacteria, hold the potential to suppress, or even terminate, such blooms, yet the nature of this interaction is not well studied. We isolated 31 cyanolytic bacteria affiliated with the genera Pseudomonas, Stenotrophomonas, Acinetobacter, and Delftia from three eutrophic freshwater lakes in Sweden and selected four phylogenetically diverse bacterial strains with strong-to-moderate lytic activity. To characterize their functional responses to the presence of cyanobacteria, we performed RNA sequencing (RNA-Seq) experiments on coculture incubations, with an initial predator-prey ratio of 1: 1. Genes involved in central cellular pathways, stress-related heat or cold shock proteins, and antitoxin genes were highly expressed in both heterotrophs and cyanobacteria. Heterotrophs in coculture expressed genes involved in cell motility, signal transduction, and putative lytic activity. L, D-Transpeptidase was the only significantly upregulated lytic gene in Stenotrophomonas rhizophila EK20. Heterotrophs also shifted their central metabolism from the tricarboxylic acid cycle to the glyoxylate shunt. Concurrently, cyanobacteria clearly show contrasting antagonistic interactions with the four tested heterotrophic strains, which is also reflected in the physical attachment to their cells. In conclusion, antagonistic interactions with cyanobacteria were initiated within 24 h, and expression profiles suggest varied responses for the different cyanobacteria and studied cyanolytes. IMPORTANCE Here, we present how gene expression profiles can be used to reveal interactions between bloom-forming freshwater cyanobacteria and antagonistic heterotrophic bacteria. Species-specific responses in both heterotrophs and cyanobacteria were identified. The study contributes to a better understanding of the interspecies cellular interactions underpinning the persistence and collapse of cyanobacterial blooms.
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| 4. |
- Ahrens, Lutz, et al.
(författare)
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Microcosm experiment to test bacterial responses to perfluorooctanoate exposure
- 2023
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 857
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Tidskriftsartikel (refereegranskat)abstract
- The impact of perfluoroalkyl and polyfluoroalkyl substances on microbial communities is challenging to investigate in situ because of the complexity and dynamics of natural ecosystems. In the present study, four microcosms were estab-lished to explore the impact of perfluorooctanoate (PFOA) on bacterial communities in riverine and marine settings. PFOA distribution between the aqueous and sedimentary phases fluctuated in both PFOA-amended and unamended control systems. PFOA was more rapidly partitioned into the sediment in marine than in riverine microcosms. Differ-ences in iron concentration and salinity may influence PFOA exchange between water and sediment. In marine micro-cosms, the alpha diversity of bacterial communities was significantly correlated to PFOA concentration. PFOA tended to correlate more strongly with bacterial community composition in water than in sediment. At the whole system level, Lefse's analysis indicated Algoriphagus halophilus as biomarkers for PFOA exposure in both riverine and marine systems, and the family Flavobacteriaceae were also more abundant in the exposed systems. In terms of temporal variation (comparison between three time points in the systems), metastat analysis showed great variability of potential PFOA-sensitive bacteria at the genus level. As such, most PFOA-sensitive genera were transitory and variable and existed for a short term in different systems (river, sea, blank, and experiment) and phases. Compared with other PFOA-sensitive genera, we suggest that further research is carried out to explore the use of Limnobacter as a bioindicator for temporal monitoring of PFOA pollution.
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| 5. |
- Alneberg, Johannes, et al.
(författare)
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Genomes from uncultivated prokaryotes : a comparison of metagenome-assembled and single-amplified genomes
- 2018
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Ingår i: Microbiome. - : BioMed Central. - 2049-2618. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Background: Prokaryotes dominate the biosphere and regulate biogeochemical processes essential to all life. Yet, our knowledge about their biology is for the most part limited to the minority that has been successfully cultured. Molecular techniques now allow for obtaining genome sequences of uncultivated prokaryotic taxa, facilitating in-depth analyses that may ultimately improve our understanding of these key organisms. Results: We compared results from two culture-independent strategies for recovering bacterial genomes: single-amplified genomes and metagenome-assembled genomes. Single-amplified genomes were obtained from samples collected at an offshore station in the Baltic Sea Proper and compared to previously obtained metagenome-assembled genomes from a time series at the same station. Among 16 single-amplified genomes analyzed, seven were found to match metagenome-assembled genomes, affiliated with a diverse set of taxa. Notably, genome pairs between the two approaches were nearly identical (average 99.51% sequence identity; range 98.77-99.84%) across overlapping regions (30-80% of each genome). Within matching pairs, the single-amplified genomes were consistently smaller and less complete, whereas the genetic functional profiles were maintained. For the metagenome-assembled genomes, only on average 3.6% of the bases were estimated to be missing from the genomes due to wrongly binned contigs. Conclusions: The strong agreement between the single-amplified and metagenome-assembled genomes emphasizes that both methods generate accurate genome information from uncultivated bacteria. Importantly, this implies that the research questions and the available resources are allowed to determine the selection of genomics approach for microbiome studies.
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| 6. |
- Alneberg, Johannes, et al.
(författare)
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Genomes from uncultivated prokaryotes: a comparison of metagenome-assembled and single-amplified genomes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Background: Prokaryotes dominate the biosphere and regulate biogeochemical processes essential to all life. Yet, our knowledge about their biology is for the most part limited to the minority that has been successfully cultured. Molecular techniques now allow for obtaining genome sequences of uncultivated prokaryotic taxa, facilitating in-depth analyses that may ultimately improve our understanding of these key organisms.Results: We compared results from two culture-independent strategies for recovering bacterial genomes: single-amplified genomes and metagenome-assembled genomes. Single-amplified genomes were obtained from samples collected at an offshore station in the Baltic Sea Proper and compared to previously obtained metagenome-assembled genomes from a time series at the same station. Among 16 single-amplified genomes analyzed, seven were found to match metagenome-assembled genomes, affiliated with a diverse set of taxa. Notably, genome pairs between the two approaches were nearly identical (>98.7% identity) across overlapping regions (30-80% of each genome). Within matching pairs, the single-amplified genomes were consistently smaller and less complete, whereas the genetic functional profiles were maintained. For the metagenome-assembled genomes, only on average 3.6% of the bases were estimated to be missing from the genomes due to wrongly binned contigs; the metagenome assembly was found to cause incompleteness to a higher degree than the binning procedure.Conclusions: The strong agreement between the single-amplified and metagenome-assembled genomes emphasizes that both methods generate accurate genome information from uncultivated bacteria. Importantly, this implies that the research questions and the available resources are allowed to determine the selection of genomics approach for microbiome studies.
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| 7. |
- Alonso-Sáez, Laura, et al.
(författare)
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High archaeal diversity in Antarctic circumpolar deep waters
- 2011
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Ingår i: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 3:6, s. 689-697
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Tidskriftsartikel (refereegranskat)abstract
- Archaea are abundant in polar oceans but important ecological aspects of this group remain enigmatic, such as patterns of diversity and biogeography. Here, we provide the first high-throughput sequencing population study of Antarctic archaea based on 198 bp fragments of the 16S rRNA gene, targeting different water masses across the Amundsen and Ross Seas. Our results suggest that archaeal commu- nity composition is strongly shaped by hydrography and significantly influenced by environmental param- eters. Archaeal communities from cold continental shelf waters (SW) of the Ross Sea were similar over depth with a single thaumarchaeal phylotype domi- nating Antarctic surface waters (AASW) and deeper SW (contributing up to 80% of reads). However, this phylotype contributed less than 8% of reads in cir- cumpolar deep waters (CDW). A related thaumar- chaeon (98% identity) was almost absent in AASW, but contributed up to 30% of reads in CDW, suggest- ing ecological differentiation of closely related phylo- types. Significantly higher archaeal richness and evenness were observed in CDW, with Shannon indices (c. 2.5) twice as high as for AASW, and high contributions of Group II Euryarchaeota. Based on these results, we suggest that CDW is a hotspot of archaeal diversity and may play an important role in the dispersal of archaeal phylotypes to other oceanic water masses.
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| 8. |
- Alonso-Saez, Laura, et al.
(författare)
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High bicarbonate assimilation in the dark by Arctic bacteria
- 2010
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Ingår i: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:12, s. 1581-1590
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Tidskriftsartikel (refereegranskat)abstract
- Although both autotrophic and heterotrophic microorganisms incorporate CO2 in the dark through different metabolic pathways, this process has usually been disregarded in oxic marine environments. We studied the significance and mediators of dark bicarbonate assimilation in dilution cultures inoculated with winter Arctic seawater. At stationary phase, bicarbonate incorporation rates were high (0.5-2.5 mu gC L-1 d(-1)) and correlated with rates of bacterial heterotrophic production, suggesting that most of the incorporation was due to heterotrophs. Accordingly, very few typically chemoautotrophic bacteria were detected by 16S rRNA gene cloning. The genetic analysis of the biotin carboxylase gene accC putatively involved in archaeal CO2 fixation did not yield any archaeal sequence, but amplified a variety of bacterial carboxylases involved in fatty acids biosynthesis, anaplerotic pathways and leucine catabolism. Gammaproteobacteria dominated the seawater cultures (40-70% of cell counts), followed by Betaproteobacteria and Flavobacteria as shown by catalyzed reporter deposition fluorescence in situ hybridization (CARDFISH). Both Beta-and Gammaproteobacteria were active in leucine and bicarbonate uptake, while Flavobacteria did not take up bicarbonate, as measured by microautoradiography combined with CARDFISH. Within Gammaproteobacteria, Pseudoalteromonas-Colwellia and Oleispira were very active in bicarbonate uptake (ca. 30 and 70% of active cells, respectively), while the group Arctic96B-16 did not take up bicarbonate. Our results suggest that, potentially, the incorporation of CO2 can be relevant for the metabolism of specific Arctic heterotrophic phylotypes, promoting the maintenance of their cell activity and/or longer survival under resource depleted conditions.
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| 9. |
- Alonso-Sáez, Laura, et al.
(författare)
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Role for urea in nitrification by polar marine Archaea
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:44, s. 17989-17994
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Tidskriftsartikel (refereegranskat)abstract
- Despite the high abundance of Archaea in the global ocean, their metabolism and biogeochemical roles remain largely unresolved. We investigated the population dynamics and metabolic activity of Thaumarchaeota in polar environments, where these microorganisms are particularly abundant and exhibit seasonal growth. Thaumarchaeota were more abundant in deep Arctic and Antarctic waters and grew throughout the winter at surface and deeper Arctic halocline waters. However, in situ single-cell activity measurements revealed a low activity of this group in the uptake of both leucine and bicarbonate (<5% Thaumarchaeota cells active), which is inconsistent with known heterotrophic and autotrophic thaumarchaeal lifestyles. These results suggested the existence of alternative sources of carbon and energy. Our analysis of an environmental metagenome from the Arctic winter revealed that Thaumarchaeota had pathways for ammonia oxidation and, unexpectedly, an abundance of genes involved in urea transport and degradation. Quantitative PCR analysis confirmed that most polar Thaumarchaeota had the potential to oxidize ammonia, and a large fraction of them had urease genes, enabling the use of urea to fuel nitrification. Thaumarchaeota from Arctic deep waters had a higher abundance of urease genes than those near the surface suggesting genetic differences between closely related archaeal populations. In situ measurements of urea uptake and concentration in Arctic waters showed that small-sized prokaryotes incorporated the carbon from urea, and the availability of urea was often higher than that of ammonium. Therefore, the degradation of urea may be a relevant pathway for Thaumarchaeota and other microorganisms exposed to the low-energy conditions of dark polar waters.
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| 10. |
- Alonso-Saez, Laura, et al.
(författare)
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Winter bloom of a rare betaproteobacteriurn in the Arctic Ocean
- 2014
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 5, s. 425-
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Tidskriftsartikel (refereegranskat)abstract
- Extremely low abundance microorganisms (members of the "rare biosphere") are believed to include dormant taxa, which can sporadically become abundant following environmental triggers. Yet, microbial transitions from rare to abundant have seldom been captured in situ, and it is uncertain how widespread these transitions are. A bloom of a single ribotype (>= 99% similarity in the 16S ribosomal RNA gene) of a widespread betaproteobacterium (Janthinobacterium sp.) occurred over 2 weeks in Arctic marine waters. The Janthinobactenum population was not detected microscopically in situ in January and early February, but suddenly appeared in the water column thereafter, eventually accounting for up to 20% of bacterial cells in mid February. During the bloom, this bacterium was detected at open water sites up to 50 km apart, being abundant down to more than 300 m. This event is one of the largest monospecific bacterial blooms reported in polar oceans. It is also remarkable because Betaproteobacteria are typically found only in low abundance in marine environments. In particular, Janthinobacterium were known from non-marine habitats and had previously been detected only in the rare biosphere of seawater samples, including the polar oceans. The Arctic Janthinobacterium formed mucilagenous monolayer aggregates after short (ca. 8 h) incubations, suggesting that biofilm formation may play a role in maintaining rare bacteria in pelagic marine environments. The spontaneous mass occurrence of this opportunistic rare taxon in polar waters during the energy-limited season extends current knowledge of how and when microbial transitions between rare and abundant occur in the ocean.
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| 11. |
- Andersen, Thomas, et al.
(författare)
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C-X-C Ligand 16 Is an Independent Predictor of Cardiovascular Death and Morbidity in Acute Coronary Syndromes
- 2019
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Ingår i: Arteriosclerosis, Thrombosis and Vascular Biology. - 1079-5642 .- 1524-4636. ; 39:11, s. 2402-2410
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Tidskriftsartikel (refereegranskat)abstract
- Objective:The chemokine CXCL16 (C-X-C motif ligand 16) is a scavenger receptor for OxLDL (oxidized low-density lipoproteins) and involved in inflammation at sites of atherosclerosis. This study aimed to investigate the association of CXCL16 with clinical outcome in patients with acute coronary syndrome.Approach and Results:Serial measurements of CXCL16 were performed in a subgroup of 5142 patients randomized in the PLATO trial (Platelet Inhibition and Patient Outcome). Associations between CXCL16 and a composite of cardiovascular death, spontaneous myocardial infarction or stroke, and the individual components were assessed by multivariable Cox regression analyses. The hazard ratio per 50% increase in admission levels of CXCL16 analyzed as continuous variable was 1.64 (95% CI, 1.44-1.88), P<0.0001. This association remained statistically significant after adjustment for randomized treatment, clinical variables, CRP (C-reactive protein), leukocytes, cystatin C, NT-proBNP (N-terminal pro-brain natriuretic peptide), troponin T, GDF-15 (growth differentiation factor 15), and other biomarkers; hazard ratio 1.23 (1.05-1.45), P=0.0126. The admission level of CXCL16 was independently associated with cardiovascular death (1.50 [1.17-1.92], P=0.0014) but not with ischemic events alone, in fully adjusted analyses. No statistically independent association was found between CXCL16 measured at 1 month, or change in CXCL16 from admission to 1 month, and clinical outcomes.Conclusions:In patients with acute coronary syndrome, admission level of CXCL16 is independently related to adverse clinical outcomes, mainly driven by an association to cardiovascular death. Thus, CXCL16 measurement may enhance risk stratification in patients with this condition.
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| 12. |
- Andersson, Annica, et al.
(författare)
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Paths to a sustainable food sector guided by LCA – exemplified by pork production
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To describe a more sustainable food sector, a supply chain approach is needed. Changing supply chains inevitably means that a range of attributes of the product and its system will change. This project will take on this challenge and deliver detailed descriptions of supply chains of six commodities from a Swedish region in 2012; Milk, cheese, beef, pork, chicken and bread. The set-up of the project was that experts on production along the supply chain design environmentally improved systems. The next step was to challenge the improvements considering their possible consequences on products and systems from different perspectives: food safety, sensory qualities, animal welfare, and consumer appreciation and (only for primary production) costs. The final supply chains were quantified by life cycle assessment (LCA), and they were again assessed from the perspectives mentioned above. Results will be generated during August 2014 and comprise both single-product LCA and region-wide impacts of the future scenarios.
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| 13. |
- Andersson, Anders, et al.
(författare)
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Pyrosequencing reveals contrasting seasonal dynamics of taxa within Baltic Sea bacterioplankton communities
- 2010
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Ingår i: ISME JOURNAL. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:2, s. 171-181
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Tidskriftsartikel (refereegranskat)abstract
- Variation in traits causes bacterial populations to respond in contrasting ways to environmental drivers. Learning about this will help us understand the ecology of individual populations in complex ecosystems. We used 454 pyrosequencing of the hypervariable region V6 of the 16S rRNA gene to study seasonal dynamics in Baltic Sea bacterioplankton communities, and link community and population changes to biological and chemical factors. Surface samples were collected from May to October 2003 and in May 2004 at the Landsort Deep in the central Baltic Sea Proper. The analysis rendered, on average, 20 200 sequence reads for each of the eight samples analyzed, providing the first detailed description of Baltic Sea bacterial communities. Community composition varied dramatically over time, supporting the idea of strong temporal shifts in bacterioplankton assemblages, and clustered according to season (including two May samples from consecutive years), suggesting repeatable seasonal succession. Overall, community change was most highly correlated with change in phosphorus concentration and temperature. Individual bacterial populations were also identified that tightly co-varied with different Cyanobacteria populations. Comparing the abundance profiles of operational taxonomic units at different phylogenetic distances revealed a weak but significant negative correlation between abundance profile similarity and genetic distance, potentially reflecting habitat filtering of evolutionarily conserved functional traits in the studied bacterioplankton.
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| 14. |
- Bagatini, Inessa Lacativa, et al.
(författare)
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Host-Specificity and Dynamics in Bacterial Communities Associated with Bloom-Forming Freshwater Phytoplankton
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:1, s. e85950-
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Tidskriftsartikel (refereegranskat)abstract
- Many freshwater phytoplankton species have the potential to form transient nuisance blooms that affect water quality and other aquatic biota. Heterotrophic bacteria can influence such blooms via nutrient regeneration but also via antagonism and other biotic interactions. We studied the composition of bacterial communities associated with three bloom-forming freshwater phytoplankton species, the diatom Aulacoseira granulata and the cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii. Experimental cultures incubated with and without lake bacteria were sampled in three different growth phases and bacterial community composition was assessed by 454-Pyrosequencing of 16S rRNA gene amplicons. Betaproteobacteria were dominant in all cultures inoculated with lake bacteria, but decreased during the experiment. In contrast, Alphaproteobacteria, which made up the second most abundant class of bacteria, increased overall during the course of the experiment. Other bacterial classes responded in contrasting ways to the experimental incubations causing significantly different bacterial communities to develop in response to host phytoplankton species, growth phase and between attached and free-living fractions. Differences in bacterial community composition between cyanobacteria and diatom cultures were greater than between the two cyanobacteria. Despite the significance, major differences between phytoplankton cultures were in the proportion of the OTUs rather than in the absence or presence of specific taxa. Different phytoplankton species favoring different bacterial communities may have important consequences for the fate of organic matter in systems where these bloom forming species occur. The dynamics and development of transient blooms may also be affected as bacterial communities seem to influence phytoplankton species growth in contrasting ways.
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| 15. |
- Bakar, Muhammad Abu, 1969-, et al.
(författare)
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Contribution of Leakage Flux to the total Losses in Transformers with Magnetic Shunt
- 2021
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Ingår i: International journal of electronics (Print). - London : Taylor & Francis Group. - 0020-7217 .- 1362-3060. ; 108:4, s. 558-573
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Tidskriftsartikel (refereegranskat)abstract
- To execute soft switching methods in resonant power converters, transformers with larger leakage inductance are getting more attention. Many papers have constructed various concepts in this regard. However, a discussion about, how the transformer efficiency is affected is lacking in the literature. This paper analyses the effects of the increased leakage inductance on the performance of the transformer. A transformer for increased leakage inductance is modelled and constructed to investigate the losses. The model discusses the effects of increased leakage inductance either by increasing the inter-winding spacing or by integrating the magnetic shunt within the transformer. The investigations show that increasing the leakage inductance by inserting a magnetic shunt can have severe degrading effects on the performance of the transformer, if not designed adequately. Additional losses are also calculated and the effects are verified by the experiments.
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| 16. |
- Barouillet, Cécilia, et al.
(författare)
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Investigating the effects of anthropogenic stressors on lake biota using sedimentary DNA
- 2022
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 68:11, s. 1799-1817
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of sedimentary DNA (sedDNA) have increased exponentially over the last decade and hold great potential to study the effects of anthropogenic stressors on lake biota over time.Herein, we synthesise the literature that has applied a sedDNA approach to track historical changes in lake biodiversity in response to anthropogenic impacts, with an emphasis on the past c. 200 years.We identified the following research themes that are of particular relevance: (1) eutrophication and climate change as key drivers of limnetic communities; (2) increasing homogenisation of limnetic communities across large spatial scales; and (3) the dynamics and effects of invasive species as traced in lake sediment archives.Altogether, this review highlights the potential of sedDNA to draw a more comprehensive picture of the response of lake biota to anthropogenic stressors, opening up new avenues in the field of paleoecology by unrevealing a hidden historical biodiversity, building new paleo-indicators, and reflecting either taxonomic or functional attributes.Broadly, sedDNA analyses provide new perspectives that can inform ecosystem management, conservation, and restoration by offering an approach to measure ecological integrity and vulnerability, as well as ecosystem functioning.
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| 17. |
- Beier, Sara, et al.
(författare)
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Bacterial chitin degradation : mechanisms and ecophysiological strategies
- 2013
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 4, s. 149-
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Forskningsöversikt (refereegranskat)abstract
- Chitin is one the most abundant polymers in nature and interacts with both carbon and nitrogen cycles. Processes controlling chitin degradation are summarized in reviews published some 20 years ago, but the recent use of culture-independent molecular methods has led to a revised understanding of the ecology and biochemistry of this process and the organisms involved. This review summarizes different mechanisms and the principal steps involved in chitin degradation at a molecular level while also discussing the coupling of community composition to measured chitin hydrolysis activities and substrate uptake. Ecological consequences are then highlighted and discussed with a focus on the cross feeding associated with the different habitats that arise because of the need for extracellular hydrolysis of the chitin polymer prior to metabolic use. Principal environmental drivers of chitin degradation are identified which are likely to influence both community composition of chitin degrading bacteria and measured chitin hydrolysis activities.
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| 18. |
- Beier, Sara
(författare)
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Bacterial Degradation and Use of Chitin in Aquatic Habitats
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chitin belongs to the most abundant biopolymers on earth where it has an important role as a structural element in crustaceans, insects, fungi and some phytoplankton. Missing evidence for long-term accumulation of chitin in nature implies fast turnover and as chitin is composed of aminosugar subunits it holds central roles in both carbon and nitrogen cycles. The aim of this thesis was to contribute to a better understanding of organic matter cycling by learning more about the diversity, function and ecology of bacteria that degrade chitin. A metagenome-enabled study of the spatial distribution of chitinolytic bacteria in aquatic ecosystems identified salinity as the major environmental factor for shaping their community composition. To address the role of alternative environmental variables controlling chitinolytic communities, a temporally resolved study was completed in a dimictic freshwater lake. Pronounced seasonal change in the indigenous chitinolytic community was observed and parallel measured environmental parameters pointed to the availability and crystalline form of chitin as significant controlling factors. The different ecological niches occupied by microbes that utilize chitin for growth were studied in an experimental study. Single-cell quantification of chitinolytic cells and cells incorporating chitin hydrolysis products suggested that commensal use of chitin hydrolysis products without simultaneous chitinase activity could be an important ecological strategy in freshwater bacterioplankton communities. Members of the ubiquitous and often quantitatively dominant group of freshwater Actinobacteria Ac1 were identified as particularly active in this “cheater” lifestyle. Further experiments based on artificially created gradients in bacterial diversity demonstrated the importance of specific bacterial populations and community composition rather than overall community richness in controlling more specific functions such as chitin and cellulose degradation. To conclude, results of this thesis provide insight into the biogeography, niche-separation and species interactions of the functional community of chitin degraders and the influence of general bacterial diversity to the respective system functioning.
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| 19. |
- Beier, Sara, et al.
(författare)
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Betaproteobacterial ammonia oxidizers in root zones of aquatic macrophytes
- 2010
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Ingår i: Fundamental and Applied Limnology. - : Schweizerbart. - 1863-9135. ; 177:4, s. 241-255
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced nitrification and coupled denitrification in macrophyte root zones may contribute to the depletion of nitrogen from the rhizosphere and are both critical processes for agriculture and rhizoremediation. We examined one factor likely to affect these processes: the ammonia oxidizing betaproteobacterial community composition, and whether or not it is influenced by plant species (Eleocharis acicularis, Eleocharis palustris, Typha angustifolia) or sediment characteristics. Genes coding for ammonia monooxygenase (amoA) and 16S rRNA of betaproteobacterial ammonia oxidizers were targeted. The betaproteobacterial ammonia oxidizing community in root surface biofilms was distinct from the surrounding rhizosphere sediment. In contrast, communities in rhizosphere and bulk sediment samples were very similar. Our results showed the occurrence of Nitrosomonas europaea-like bacteria nearly exclusively in the rhizoplane biofilms, while sequences affiliated with the Nitrosomonas oligotropha, Nitrosomonas communis and Nitrosospira-lineages were more frequently detected in the surrounding sediment. Our results further suggest that the presence of N. europaea on macrophyte roots depends on the sampling site rather than on the studied macrophyte species. We propose that the rhizoplane of aquatic macrophytes is a natural habitat for N. europaea.
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| 20. |
- Beier, Sara, et al.
(författare)
-
Global Phylogeography of Chitinase Genes in Aquatic Metagenomes
- 2011
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 77:3, s. 1101-1106
-
Tidskriftsartikel (refereegranskat)abstract
- Phylogeny-based analysis of chitinase and 16S rRNA genes from metagenomic data suggests that salinity is a major driver for the distribution of both chitinolytic and total bacterial communities in aquatic systems. Additionally, more acidic chitinase proteins were observed with increasing salinity. Congruent habitat separation was further observed for both genes according to latitude and proximity to the coastline. However, comparison of chitinase and 16S rRNA genes extracted from different geographic locations showed little congruence in distribution. There was no indication that dispersal limited the global distribution of either gene.
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| 21. |
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| 22. |
- Beier, Sara, et al.
(författare)
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Pronounced seasonal dynamics of freshwater chitinase genes and chitin processing
- 2012
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 14:9, s. 2467-2479
-
Tidskriftsartikel (refereegranskat)abstract
- Seasonal variation in activity of enzymes involved in polymer degradation, including chitinases, has been observed previously in freshwater environments. However, it is not known whether the seasonal dynamics are due to shifts in the activity of bacteria already present, or shifts in community structure towards emergence or disappearance of chitinolytic organisms. We traced seasonal shifts in the chitinase gene assemblage in a temperate lake and linked these communities to variation in chitinase activity. Chitinase genes from 20 samples collected over a full yearly cycle were characterized by pyrosequencing. Pronounced temporal shifts in composition of the chitinase gene pool (beta diversity) occurred along with distinct shifts in richness (alpha diversity) as well as chitin processing. Changes in the chitinase gene pool correlated mainly with temperature, abundance of crustacean zooplankton and phytoplankton blooms. Also changes in the physical structure of the lake, e.g. stratification and mixing were associated with changes in the chitinolytic community, while differences were minor between surface and suboxic hypolimnetic water. The lake characteristics influencing the chitinolytic community are all linked to changes in organic particles and we suggest that seasonal changes in particle quality and availability foster microbial communities adapted to efficiently degrade them.
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| 23. |
- Beier, Sara, et al.
(författare)
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Uncoupling of chitinase activity and uptake of hydrolyses products in freshwater bacterioplankton
- 2011
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 56:4, s. 1179-1188
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated to what extent chitinolytic bacteria subsidize bacterial populations that do not produce chitinolytic enzymes but still use the products of chitin hydrolysis. Applying single-cell techniques to untreated and chitin-enriched lake water, we show that the number of planktonic cells taking up chitin hydrolysis products by far exceeds the number of cells expressing chitinases. Flavobacteria, Actinobacteria, and specifically members of the abundant and ubiquitous freshwater Ac1 cluster of the Actinobacteria, increased in abundance and were enriched in response to the chitin amendment. Flavobacteria were frequently observed in dense clusters on chitin particles, suggesting that they are actively involved in the hydrolysis and solubilization of chitin. In contrast, Actinobacteria were exclusively planktonic. We propose that planktonic Actinobacteria contain commensals specialized in the uptake of small hydrolysis products without expressing or possibly even possessing the machinery for chitin hydrolysis. More research is needed to assess the importance of such "cheater'' substrate acquisition strategies in the turnover and degradation of polymeric organic matter in aquatic ecosystems.
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| 24. |
- Bendall, Matthew L, et al.
(författare)
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Genome-wide selective sweeps and gene-specific sweeps in natural bacterial populations
- 2016
-
Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 10:7, s. 1589-1601
-
Tidskriftsartikel (refereegranskat)abstract
- Multiple models describe the formation and evolution of distinct microbial phylogenetic groups. These evolutionary models make different predictions regarding how adaptive alleles spread through populations and how genetic diversity is maintained. Processes predicted by competing evolutionary models, for example, genome-wide selective sweeps vs gene-specific sweeps, could be captured in natural populations using time-series metagenomics if the approach were applied over a sufficiently long time frame. Direct observations of either process would help resolve how distinct microbial groups evolve. Here, from a 9-year metagenomic study of a freshwater lake (2005-2013), we explore changes in single-nucleotide polymorphism (SNP) frequencies and patterns of gene gain and loss in 30 bacterial populations. SNP analyses revealed substantial genetic heterogeneity within these populations, although the degree of heterogeneity varied by >1000-fold among populations. SNP allele frequencies also changed dramatically over time within some populations. Interestingly, nearly all SNP variants were slowly purged over several years from one population of green sulfur bacteria, while at the same time multiple genes either swept through or were lost from this population. These patterns were consistent with a genome-wide selective sweep in progress, a process predicted by the /`ecotype model/' of speciation but not previously observed in nature. In contrast, other populations contained large, SNP-free genomic regions that appear to have swept independently through the populations prior to the study without purging diversity elsewhere in the genome. Evidence for both genome-wide and gene-specific sweeps suggests that different models of bacterial speciation may apply to different populations coexisting in the same environment.
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| 25. |
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| 26. |
- Bertilsson, Magnus, et al.
(författare)
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Goldberger-Treiman relation and Wu-type experiment in the decuplet sector
- 2024
-
Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 109:3
-
Tidskriftsartikel (refereegranskat)abstract
- The leading-order chiral Lagrangian for the baryon octet and decuplet states coupled to Goldstone bosons and external sources contains six low-energy constants. Five of them are fairly well-known from phenomenology, but the sixth one is practically unknown. This coupling constant provides the strength of the (p-wave) coupling of Goldstone bosons to decuplet states. Its size and even sign are under debate. Quark models and quantum chromodynamics (QCD) for a large number of colors provide predictions, but some recent phenomenological analyses even suggest an opposite sign for the Delta -pion coupling. The Goldberger-Treiman relation connects this coupling constant to the axial charge of the Delta baryon. This suggests a Wu-type experiment to determine the unknown low-energy constant. While this is not feasible in the Delta sector because of the large hadronic width of the Delta, there is a flavor symmetry related process that is accessible; the weak semileptonic decay of the Omega baryon to a spin 3/2 cascade baryon. A broad research program is suggested that can pin down at least the rough size and the sign of the last unknown low-energy constant of the leading-order Lagrangian. It encompasses experimental measurements, in particular the forward-backward asymmetry of the semileptonic decay, together with a determination of the quark-mass dependences using lattice QCD for the narrow decuplet states and chiral perturbation theory to extrapolate to the Delta sector. Besides discussing the strategy of the research program, the present work provides a feasibility check based on a simple leading-order calculation.
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| 27. |
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| 28. |
- Bertilsson, Stefan, et al.
(författare)
-
Diversity and Dynamics of Bacterial Communities in Freshwater Lakes
- 2022
-
Ingår i: Encyclopedia of Inland Waters (Second Edition). - 9780128191668 ; 1, s. 601-615
-
Bokkapitel (refereegranskat)abstract
- Freshwater lakes host phylogenetically diverse microbes that are playing significant roles in elemental cycling in these ecosystems. In this chapter we present an accessible overview of the present knowledge of lake bacteria, their diversity, metabolism, and dynamics. The resolution offered by state-of-the-art metagenomics and single cell genomics approaches now provide unprecedented insights into the metabolic capabilities of yet to be cultured lake bacteria. These insights show that adaptations in predominant lake bacteria to low nutrient concentrations has led to the development of an intertwined network of metabolic dependencies in the bacterioplankton where exploration of how this is reflected in their dynamics and realized biogeochemical functions are in progress. While lakes across the world represent heterogeneous ecosystems, charismatic lake bacteria are globally distributed, and their dynamics is structured via the influence of both resource availability (bottom-up controls) and food web interactions (top-down controls). A prospective challenge to be addressed in future studies would be to more directly link functional traits of lake bacteria with their distribution patterns and to disentangle the implication of food web interactions on these traits. Ultimately this combined information can be used to develop mechanistic, informative, and robust models of “ecosystem metabolism” that offer capabilities to forecast ecosystem change due to climate impacts.
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| 29. |
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| 30. |
- Bertilsson, Stefan
(författare)
-
Fluorescently labeled prey surrogates in combination with fluorescence-activated cell sorting successfully discriminate actively feeding mixotrophs in a lake water sample
- 2024
-
Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 69, s. 1030-1044
-
Tidskriftsartikel (refereegranskat)abstract
- Mixotrophic protists are capable of acting both as primary producers and primary consumers at the base of the aquatic food web, thus constituting key organisms in ecosystems where they are abundant. However, their identity, abundance, ecological dynamics, and biogeochemical impact in aquatic ecosystems remain understudied in comparison to classically demarcated autotrophs or heterotrophs. In this study, we make use of fluorescently labeled prey and fluorescence-activated cell sorting to taxonomically identify actively-feeding individual mixotrophic flagellates from lake water. Replicated experiments were carried out to assess the performance of three different fluorescently labeled prey types and a fluorescent dye targeting food vacuoles. In the experiments, water from an oligotrophic lake was exposed independently to each type of reporter and cells were individually sorted based on fluorescent signals for predation and chlorophyll a. A total of 927 individual single cells were successfully recovered, with all fluorescent reporters exhibiting high sensitivity for putative mixotrophic taxa: overall, 87% of the occurrences could be assigned to dictyochophytes, 9% to chrysophytes, and 3% to dinoflagellates. As a result, we were able to detect cryptic diversity within pedinellid algae and report a Prorocentrum-like freshwater occurrence. We argue that this procedure can be a valuable tool to uncover relevant and unexpected active mixotrophic species in a wider range of aquatic environments, and could easily be coupled to other techniques to describe the finer details of the trophic status of aquatic microbial communities.
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| 31. |
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| 32. |
- Bertilsson, Stefan
(författare)
-
Hydrostatic pressure influence activity and assembly of bacterial communities in reservoir sediments
- 2021
-
Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 66, s. 1049-1059
-
Tidskriftsartikel (refereegranskat)abstract
- Reservoir sediments are subjected to highly variable hydrostatic pressures, but little is known about the direct impacts of this environmental variable on microbial communities and biogeochemical processes mediated by microbes in the numerous deep reservoirs (>100 m) scattered across our planet.To address this gap, the organic matter degradation and community assembly of sediment bacteria were studied in bioreactors maintained under different hydrostatic pressures (0.5-3.0 MPa) and explored using 16S rRNA amplicon sequencing analysis.Our results showed that rates of CO2 and CH4 production and microbial activity decreased significantly with increasing pressure, at least when exceeding 1.0 MPa. In contrast, alpha-diversity and community structure of the active (16S rRNA) and total (16S rRNA gene) bacterial communities did not show any significant response to the different hydrostatic pressures, but a co-occurrence network demonstrated that interactions between bacterial populations were stronger at higher pressures (>= 1.5 MPa).Moreover, ecological null model analyses revealed that when the pressure exceeded 1.5 MPa, the main assembly processes of bacterial communities changed from stochastic to deterministic. These findings corroborate an important role of pressure in the assembly and emerging interactions within sediment bacterial communities.Our results imply that increased hydrostatic pressure caused by dam constructions may hamper the metabolism of the sediment microbiota, and that this may result in enhanced sediment burial of nutrients and organic matter, at least when pressures exceed 1.0 MPa.
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| 33. |
- Bertilsson, Stefan
(författare)
-
Influence of rapid vertical mixing on bacterial community assembly in stratified water columns
- 2024
-
Ingår i: Environmental Research. - 0013-9351 .- 1096-0953. ; 243
-
Tidskriftsartikel (refereegranskat)abstract
- Water column mixing homogenizes thermal and chemical gradients which are known to define distribution of microbial communities and influence the prevailing biogeochemical processes. Little is however known about the effects of rapid water column mixing on the vertical distribution of microbial communities in stratified reser-voirs. To address this knowledge gap, physicochemical properties and microbial community composition from 16 S rRNA amplicon sequencing were analyzed before and after mixing of vertically stratified water-column bioreactors. Our results showed that alpha-diversity of bacterial communities decreased from bottom to surface during periods of thermal stratification. After an experimental mixing event, bacterial community diversity experienced a significant decrease throughout the water column and network connectivity was disrupted, fol-lowed by slow recovery. Significant differences in composition were seen for both total (DNA) and active (RNA) bacterial communities when comparing surface and bottom layer during periods of stratification, and when comparing samples collected before mixing and after re-stratification. The dominant predicted community as-sembly processes for stratified conditions were deterministic while such processes were less important during recovery from episodic mixing. Water quality characteristics of stratified water were significantly correlated with bacterial community diversity and structure. Furthermore, structural equation modeling analyses showed that changes in sulfur may have the greatest direct effect on bacterial community composition. Our results imply that rapid vertical mixing caused by episodic weather extremes and hydrological operations may have a long-term effect on microbial communities and biogeochemical processes.
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| 34. |
- Bertilsson, Stefan, et al.
(författare)
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Influence of solar radiation on the availability of dissolved organic matter to bacteria in the Southern Ocean
- 2004
-
Ingår i: Deep-Sea Research II: Topical Studies in Oceanography. - : Elsevier BV. ; 51, s. 2557-2568
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of solar radiation on the ability of dissolved organic matter (DOM) to support bacterial growth, was studied in the eastern Atlantic sector of the Southern Ocean during the SWEDARP 1997/1998 cruise with SA Agulhas December 1997–February 1998. Vertical profiles of water samples (2–3000 m) were obtained from the Spring Ice Edge (SIE, 60°S, high chlorophyll-a) and from the Winter Ice Edge (WIE, 56°S, low chlorophyll-a) areas. Filter-sterilized water from each area and depth was incubated under natural solar radiation and in the dark for comparison. Photobleaching of humic substance fluorescence occurred in all studied water samples. The bleaching was typically larger in the initially more fluorescent deep waters, compared to the low-fluorescent surface waters. Both the irradiated water and the dark controls were re-inoculated with a mixed bacterial inoculum from the initially sampled water. Bacterial growth (accumulating cells) and bacterial production (protein synthesis) were monitored during a 16–19 day incubation of these cultures at near in situ temperature (2 °C). Bacterial growth in cultures prepared from SIE water was largest at the surface (2–25 m), while the growth in corresponding cultures from the WIE did not vary much over depth. In contrast to the observed photobleaching, no clear effects of the irradiation on the ability of the DOM to support bacterial growth could be observed in either of the experiments. Hence, the degradation of fluorescent structures and other photochemical alterations of the organic matter did not have a major effect on the total pool of biodegradable organic substrates. The lack of effects of photoreactions on bacterial growth potential in the present study disagrees with the short-term bacterial growth response observed in other oceanic environments. This could be due to the different experimental approaches employed (short-vs. long-term incubations) or may indicate that the impact of photoreactions on bacterial growth in the Southern Ocean differ substantially from aquatic systems that are more influenced by terrestrial environments, as well as the warmer oligotrophic oceanic environments.
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| 35. |
- Bertilsson, Stefan
(författare)
-
Integrating experiments with system-level biogeochemical modeling to understand nitrogen cycling of reservoir sediments at elevated hydrostatic pressure
- 2021
-
Ingår i: Environmental Research. - : Elsevier BV. - 0013-9351 .- 1096-0953. ; 200
-
Tidskriftsartikel (refereegranskat)abstract
- Impoundment of rivers to construct reservoirs for hydropower and irrigation greatly increase the hydrostatic pressure acting on river sediments with potential repercussions for ecosystem-level microbial activity and metabolism. Understanding the functioning and responses of key biogeochemical cycles such as that of nitrogen cycling to shifting hydrostatic pressure is needed to estimate and predict the systemic nutrient dynamics in deepwater reservoirs. We studied the functioning of bacterial communities involved in nitrogen transformation in bioreactors maintained under contrasting hydrostatic pressures (0.5 MPa-3.0 MPa) and complemented the experimental approach with a functional gene-informed biogeochemical model. The model predictions were broadly consistent with observations from the experiment, suggesting that the rates of N2O production decreased while the sediment concentration of nitrite increased significantly with increasing pressure, at least when exceeding 1.0 MPa. Changes in nitrite reduction (nirS) and aerobic ammonia oxidation (amoA) genes abundances were in accordance with the observed changes in N2O production and nitrite levels. Moreover, the model predicted that the higher pressures (P > 1.5 MPa) would intensify the inhibition of N2 production via denitrification and result in an accumulation of ammonia in the sediment along with a decrease in dissolved oxygen. The results imply that increased hydrostatic pressure caused by dam constructions may have a strong effect on microbial nitrogen conversion, and that this may result in lower nitrogen removal.
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| 36. |
- Bertilsson, Stefan, et al.
(författare)
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Links between bacterial production, amino acid utilization and community composition in productive lakes
- 2007
-
Ingår i: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 1:6, s. 532-544
-
Tidskriftsartikel (refereegranskat)abstract
- Influence of distribution and abundance of bacterial taxa on ecosystem function are poorly understood for natural microbial communities. We related 16S rRNA-based terminal restriction fragment length polymorphism to bacterial production and arginine uptake kinetics to test if functional features of bacterioplankton in four lakes could be predicted from community composition. Maximum arginine uptake rate (arginine Vmax) ranged from 10% to 100% of bacterial production. Owing to high growth efficiencies on arginine (63–77%), the bacterial community could potentially saturate its carbon demand using this single organic substrate, for example, during sudden surges of free amino acids. However, due to low in situ concentrations of arginine in these lakes (<0.9 g l-1), actual uptake rates at ambient concentrations rarely exceeded 10% of Vmax. Bacterial production and arginine Vmax could be predicted from a subset of bacterial ribotypes, tentatively affiliated with several bacterial divisions (Cyanobacteria, Actinobacteria, Bacteroidetes and Proteobacteria). Multivariate statistical analysis indicates that there were both highly important and less important ribotypes for the prediction of bacterial production and arginine Vmax. These populations were either negatively or positively related to the respective functional feature, indicating contrasting ecological roles. Our study provides a statistically robust demonstration that, apart from environmental conditions, patterns in bacterial community composition can also be used to predict lake ecosystem function.
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| 37. |
- Bertilsson, Stefan
(författare)
-
Microbial trait-based approaches for agroecosystems
- 2022
-
Ingår i: Advances in Agronomy. - : Elsevier. - 0065-2113 .- 2213-6789. ; 175, s. 259-299
-
Tidskriftsartikel (refereegranskat)abstract
- Conventional agricultural practices negatively impact soil biodiversity, carbon stocks, and greenhouse gas emissions in ways that make them unsustainable for supporting future supply of food and fiber. Better management of agrobiodiversity will likely play a critical role in transitioning toward more sustainable practices. In particular, innovation and developments targeting the aboveground and belowground components of agroecosystems should be informed by frameworks and approaches that harness the-in particular functional diversityof complex microbial communities. Here, we review and discuss microbial trait-based approaches that will help us understand and steer agroecosystem functioning in the face of global change. We highlight how trait-based approaches can improve agricultural practices related to soil functioning (e.g., soil fertility and aggregation); climate regulation (e.g., carbon storage and greenhouse gas emissions) and adaptation to climate change; plant health; and reduction of contaminant-related hazards for human health. We also consider how microbial trait-based approaches can be used as a tool to improve cultivated plant performance through artificial selection and microbiome engineering. Last, we discuss the inherent obstacles associated with the development and implementation of trait-based approaches owing to strong interactions within microbial communities and linkages between plants and the soil environment. Despite these obstacles, microbial trait-based approaches hold promise for the sustainable management of agricultural ecosystems needed to feed and nourish a rapidly growing human population.
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| 38. |
- Bertilsson, Stefan, et al.
(författare)
-
Non-cyanobacterial diazotrophs dominate nitrogen-fixing communities in permafrost thaw ponds
- 2020
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 65, s. S180-S193
-
Tidskriftsartikel (refereegranskat)abstract
- There is a growing concern about the implications of accelerated thawing of permafrost for regional biogeochemical cycling of carbon and other bioreactive elements. One such element of concern is nitrogen, and in this study, we investigated the diversity and biogeography of potential diazotrophs within a series of thaw ponds representing different ontogenetic stages in pond development. Using metagenomic sequence data from subarctic thaw ponds, we identified an array of nitrogenase genes across the ponds. The iron-only nitrogenase gene (anfH) was positively correlated with sulfate, while there was no correlation with methane despite previous findings that organisms carrying anfH can simultaneously participate in nitrogen fixation and methanogenesis. Sulfate is known to inhibit microbial uptake of molybdate, an element essential for the activity of the nifH (molybdenum-iron) nitrogenase and this may explain the high potential for nitrogen fixation utilizing anfH in sulfate-rich ponds. NifH was particularly abundant in the hypolimnion of the deeper and older ponds, with Deltaproteobacteria and Chlorobi as the putative dominant diazotrophs. In the epilimnetic waters, nifH composition was more variable, with various Gammaproteobacteria as abundant representatives, while cyanobacterial diazotrophs were scarce. Interestingly, nifH gene abundance was significantly positively correlated with in situ methane concentration. Based on genome-resolved metagenomics, we hypothesize that diazotrophs and methanogens engage in syntrophic interactions in anoxic waters, possibly via propionate oxidation or (in Geobacter) by interspecies electron transfer. Our results also suggest that nitrogen fixers may supply bioreactive nitrogen compounds to the thaw pond communities, thereby enhancing growth and activity of methanogens.
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| 39. |
- Bertilsson, Stefan, et al.
(författare)
-
Out of the blue: the independent activity of sulfur-oxidizers and diatoms mediate the sudden color shift of a tropical river
- 2023
-
Ingår i: Environmental Microbiome. - : Springer Science and Business Media LLC. - 2524-6372. ; 18
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundRio Celeste ("Sky-Blue River") is a river located in the Tenorio National Park (Costa Rica) that has become an important hotspot for eco-tourism due to its striking sky-blue color. A previous study indicated that this color is not caused by dissolved chemical species, but by formation of light-scattering aluminosilicate particles at the mixing point of two colorless streams, the acidic Quebrada Agria and the neutral Rio Buenavista.ResultsWe now present microbiological information on Rio Celeste and its two tributaries, as well as a more detailed characterization of the particles that occur at the mixing point. Our results overturn the previous belief that the light scattering particles are formed by the aggregation of smaller particles coming from Rio Buenavista, and rather point to chemical formation of hydroxyaluminosilicate colloids when Quebrada Agria is partially neutralized by Rio Buenavista, which also contributes silica to the reaction. The process is mediated by the activities of different microorganisms in both streams. In Quebrada Agria, sulfur-oxidizing bacteria generate an acidic environment, which in turn cause dissolution and mobilization of aluminum and other metals. In Rio Buenavista, the growth of diatoms transforms dissolved silicon into colloidal biogenic forms which may facilitate particle precipitation.ConclusionsWe show how the sky-blue color of Rio Celeste arises from the tight interaction between chemical and biological processes, in what constitutes a textbook example of emergent behavior in environmental microbiology.
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| 40. |
- Bertilsson, Stefan, 1969-
(författare)
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Photochemical alterations of dissolved organic matter : Impact on heterotrophic bacteria and carbon cycling in lakes
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Globally, the amount of carbon in dissolved organic matter (DOM) is similar to the total amount in the atmosphere. DOM also plays a key role in structuring natural surface waters and affects the physical, chemical, and biological character of these systems. In this thesis, the impact of solar UV radiation on the dynamics and tumover of these substances in lakes was studied, in particular concerning the influence of photochemical alterations of DOM on the transfer of carbon to heterotrophic bacteria for transfer through food webs. Substantial photoproduction of a number of low molecular weight organic acids was demonstrated, and I also showed that these photoproducts may be major substrates for heterotrophic bacterioplankton in humic surface waters. The photoproduction of these acids and the complete oxidation of DOM to CO2 occurred in waters from all studied lakes, and it was concluded that these processes could be a major sink for aquatic DOM. The impact of UV irradiation on the ability of DOM to support heterotrophic bacterial growth was strongly positive in all freshwaters with a high content of terrestrially derived organic matter, while the opposite was true for waters with a high relative contribution of algal material. Hence the quality of the DOM is probably an important factor governing the net effect of irradiation on DOM bioavailability. In conclusion, photochemical processes play a major role in the dynamics of DOM in surface waters and also influence bacterial growth by altering the size of the total pool of organic compounds available for bacterial utilization.
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| 41. |
- Bertilsson, Stefan, et al.
(författare)
-
Photochemical transformation of dissolved organic matter in lakes
- 2000
-
Ingår i: Limnology and Oceanography. - 0024-3590. ; 45, s. 753-762
-
Tidskriftsartikel (refereegranskat)abstract
- In a survey of photochemical transformation of dissolved organic matter (DOM) in lake water, we found photochemical production of dissolved inorganic carbon (DIC) and low molecular weight carboxylic acids (oxalic, malonic, formic, and acetic acid), upon s
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| 42. |
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| 43. |
- Bertilsson, Stefan, et al.
(författare)
-
Photochemically induced changes in bioavailable carbon and nitrogen pools in a boreal watershed
- 1999
-
Ingår i: Aquatic Microbial Ecology. - Oldendorf : Inter-Research. - 0948-3055 .- 1616-1564. ; 19:1, s. 47-56
-
Tidskriftsartikel (refereegranskat)abstract
- In several recent studies, a net stimulation of bacterial growth has been demonstrated after exposing humic surface waters to solar radiation or artificial ultraviolet radiation. This stimulation has been attributed to a photochemical release of bioavailable carbon or nitrogen compounds (ammonium). In a synoptic experiment, we exposed 0.2 mu m filtered water from 12 different habitats in a river system, dominated by allochthonous carbon input, to mild artificial UV radiation. A significant photochemical release of carboxylic acids of low molecular weight occurred. Furthermore, the exposure increased carbon-limited bacterial yield on average by a factor of 1.7. No photochemical production of free ammonium could be detected, which was in accordance with the lack of effects of radiation on bacterial growth yield under nitrogen-limited conditions. We conclude that, in boreal systems dominated by allochthonous carbon input, photochemical production of bioavailable carbon rather than nitrogen compounds is likely to positively influence the total substrate pool available for bacterial utilization.
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| 44. |
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| 45. |
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| 46. |
- Bertilsson, Stefan
(författare)
-
Properly interpret metabolic inhibition results to identify primary mercury methylating microbes
- 2023
-
Ingår i: Critical Reviews in Environmental Science and Technology. - : Informa UK Limited. - 1064-3389 .- 1547-6537. ; 53, s. 1757-1773
-
Forskningsöversikt (refereegranskat)abstract
- Distinguishing the respective contributions of various microbes to methylmercury (MeHg) production is critical for predicting MeHg bioaccumulation and exposure risk. Metabolic inhibitors have been commonly used to block the activity of specific microbial groups and identify primary Hg methylating microbes. By reviewing literatures and our empirical data, we demonstrate how multiple factors, including (1) the addition of inappropriate amounts of inhibitors, (2) a tendency to overlook microbial syntrophy, and (3) the absence of comprehensive proxy systems of Hg methylation, would impact result interpretation of this approach. We thus suggest that the design of inhibition assays should consider the environmental properties, e.g., background levels of electron acceptors, concentrations of metabolic substrates, and abundances of Hg methylating microbes. We also recommend that inhibitors should be added at multiple concentrations and that observed changes in Hg methylation should be assessed with comprehensive indicators. Revealing the key factors responsible for the improper usage of this method and inadequate interpretation of the results would help optimize inhibition assays for robust predictions of MeHg production in nature.
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| 47. |
- Bertilsson, Stefan
(författare)
-
Regional factors as major drivers for microbial community turnover in tropical cascading reservoirs
- 2022
-
Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- The turnover of microbial communities across space is dictated by local and regional factors. Locally, selection shapes community assembly through biological interactions between organisms and the environment, while regional factors influence microbial dispersion patterns. Methods used to disentangle the effects of local and regional factors typically do not aim to identify ecological processes underlying the turnover. In this paper, we identified and quantified these processes for three operational microbial subcommunities (cyanobacteria, particle-attached, and free-living bacteria) from a tropical cascade of freshwater reservoirs with decreasing productivity, over two markedly different dry and rainy seasons. We hypothesized that during the dry season communities would mainly be controlled by selection shaped by the higher environmental heterogeneity that results from low hydrological flow and connectivity between reservoirs. We expected highly similar communities shaped by dispersal and a more homogenized environment during the rainy season, enhanced by increased flow rates. Even if metacommunities were largely controlled by regional events in both periods, the selection had more influence on free-living communities during the dry period, possibly related to elevated dissolved organic carbon concentration, while drift as a purely stochastic factor, had more influence on cyanobacterial communities. Each subcommunity had distinct patterns of turnover along the cascade related to diversity (Cyanobacteria), lifestyle and size (Free-living), and spatial dynamics (particle-attached).
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| 48. |
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| 49. |
|
|
| 50. |
|
|
