7 results on '"Giljan, Greta"'
Search Results
2. Metabolism of a hybrid algal galactan by members of the human gut microbiome
- Author
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Robb, Craig S., Hobbs, Joanne K., Pluvinage, Benjamin, Reintjes, Greta, Klassen, Leeann, Monteith, Stephanie, Giljan, Greta, Amundsen, Carolyn, Vickers, Chelsea, Hettle, Andrew G., Hills, Rory, Nitin, Xing, Xiaohui, Montina, Tony, Zandberg, Wesley F., Abbott, D. Wade, and Boraston, Alisdair B.
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- 2022
- Full Text
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3. Correlations among carbohydrate inventories, enzyme activities, and microbial communities in the western North Atlantic Ocean.
- Author
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Lloyd, C. Chad, Brown, Sarah, Giljan, Greta, Ghobrial, Sherif, Vidal-Melgosa, Silvia, Steinke, Nicola, Hehemann, Jan-Hendrik, Amann, Rudolf, and Arnosti, Carol
- Subjects
MICROBIAL communities ,CARBOHYDRATES ,PEPTIDASE ,MICROBIAL enzymes ,EXTRACELLULAR enzymes ,BACTERIAL communities ,OCEAN - Abstract
Heterotrophic bacteria process nearly half of the organic matter produced by phytoplankton in the surface ocean. Much of this organic matter consists of high molecular weight (HMW) biopolymers such as polysaccharides and proteins, which must initially be hydrolyzed to smaller sizes by structurally specific extracellular enzymes. To assess the relationships between substrate structure and microbial community composition and function, we concurrently determined carbohydrate abundance and structural complexity, bacterial community composition, and peptidase and polysaccharide hydrolase activities throughout the water column at four distinct stations in the western North Atlantic Ocean. Although the monosaccharide constituents of particulate organic matter (POM) were similar among stations, the structural complexity of POM-derived polysaccharides varied by depth and station, as demonstrated by polysaccharide-specific antibody probing. Bacterial community composition and polysaccharide hydrolase activities also varied by depth and station, suggesting that the structure and function of bacterial communities—and the structural complexity of their target substrates—are interlinked. Thus, the extent to which bacteria can transform organic matter in the ocean is dependent on both the structural complexity of the organic matter and their enzymatic capabilities in different depths and regions of the ocean. [ABSTRACT FROM AUTHOR]
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- 2024
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4. Pulsed inputs of high molecular weight organic matter shift the mechanisms of substrate utilisation in marine bacterial communities.
- Author
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Brown, Sarah, Lloyd, C. Chad, Giljan, Greta, Ghobrial, Sherif, Amann, Rudolf, and Arnosti, Carol
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BACTERIAL communities ,ORGANIC compounds ,MOLECULAR weights ,HETEROTROPHIC bacteria ,GULF Stream ,ECOLOGICAL regime shifts - Abstract
Heterotrophic bacteria hydrolyze high molecular weight (HMW) organic matter extracellularly prior to uptake, resulting in diffusive loss of hydrolysis products. An alternative 'selfish' uptake mechanism that minimises this loss has recently been found to be common in the ocean. We investigated how HMW organic matter addition affects these two processing mechanisms in surface and bottom waters at three stations in the North Atlantic Ocean. A pulse of HMW organic matter increased cell numbers, as well as the rate and spectrum of extracellular enzymatic activities at both depths. The effects on selfish uptake were more differentiated: in Gulf Stream surface waters and productive surface waters south of Newfoundland, selfish uptake of structurally simple polysaccharides increased upon HMW organic matter addition. The number of selfish bacteria taking up structurally complex polysaccharides, however, was largely unchanged. In contrast, in the oligotrophic North Atlantic gyre, despite high external hydrolysis rates, the number of selfish bacteria was unchanged, irrespective of polysaccharide structure. In deep bottom waters (> 4000 m), structurally complex substrates were processed only by selfish bacteria. Mechanisms of substrate processing—and the extent to which hydrolysis products are released to the external environment—depend on substrate structural complexity and the resident bacterial community. [ABSTRACT FROM AUTHOR]
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- 2024
- Full Text
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5. Bacterioplankton reveal years-long retention of Atlantic deep-ocean water by the Tropic Seamount
- Author
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Giljan, Greta, Kamennaya, Nina A., Otto, Andreas, Becher, Dörte, Ellrott, Andreas, Meyer, Volker, Murton, Bramley J., Fuchs, Bernhard M., Amann, Rudolf I., and Zubkov, Mikhail V.
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- 2020
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6. Strong seasonal differences of bacterial polysaccharide utilization in the North Sea over an annual cycle.
- Author
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Giljan, Greta, Arnosti, Carol, Kirstein, Inga V., Amann, Rudolf, and Fuchs, Bernhard M.
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XYLANS , *CARBON cycle , *CHONDROITIN sulfates , *ALGAL blooms , *SEASONS , *HETEROTROPHIC bacteria , *MARINE bacteria , *POLYSACCHARIDES - Abstract
Summary: Marine heterotrophic bacteria contribute considerably to global carbon cycling, in part by utilizing phytoplankton‐derived polysaccharides. The patterns and rates of two different polysaccharide utilization modes – extracellular hydrolysis and selfish uptake – have previously been found to change during spring phytoplankton bloom events. Here we investigated seasonal changes in bacterial utilization of three polysaccharides, laminarin, xylan and chondroitin sulfate. Strong seasonal differences were apparent in mode and speed of polysaccharide utilization, as well as in bacterial community compositions. Compared to the winter month of February, during the spring bloom in May, polysaccharide utilization was detected earlier in the incubations and a higher portion of all bacteria took up laminarin selfishly. Highest polysaccharide utilization was measured in June and September, mediated by bacterial communities that were significantly different from spring assemblages. Extensive selfish laminarin uptake, for example, was detectible within a few hours in June, while extracellular hydrolysis of chondroitin was dominant in September. In addition to the well‐known Bacteroidota and Gammaproteobacteria clades, the numerically minor verrucomicrobial clade Pedosphaeraceae could be identified as a rapid laminarin utilizer. In summary, polysaccharide utilization proved highly variable over the seasons, both in mode and speed, and also by the bacterial clades involved. [ABSTRACT FROM AUTHOR]
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- 2022
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7. Flow sorting of marine bacteria for targeted metabolic studies
- Author
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Giljan, Greta, Fuchs, Bernhard, and Arnosti, Carol
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marine carbon cycling ,flow cytometry ,ddc:500 ,500 Science ,polysaccharide utilization - Abstract
Half of Earth’s primary production takes place in the marine environment, where CO2 from the atmosphere is transformed by marine phytoplankton into organic biomass. This newly produced biomass is then rapidly consumed by heterotrophic microorganisms such as bacteria and archaea. Heterotrophic microorganisms thus contribute to a large part of the turnover of carbon in the ocean, affecting the global carbon cycle. Among the complex communities of marine microorganisms, the contribution of individual organisms to the utilization of organic matter can vary greatly, depending on the type of organic matter and the organism’s specific capabilities for substrate processing. The focus of this work was on the targeted identification of metabolically active bacteria. The first two chapters deal with the bacterial utilization of polysaccharides, a type of substrate that can only be utilized by some members of microbial communities, even though it is one of the main constituents of freshly produced photosynthetic biomass. The first chapter provides methodological guidelines for incubation experiments with fluorescently labeled polysaccharides (FLA-PS) that can be used to simultaneously investigate extracellular hydrolysis and selfish uptake – two distinct modes of bacterial polysaccharide utilization. Using FLA-PS incubation experiments, we could show in chapter 2 the balance of both polysaccharide utilization mechanisms at Helgoland over the course of a year, with increasing and more rapid selfish uptake for laminarin and xylan towards summer and a shift to high rates of extracellular hydrolysis for xylan and chondroitin sulfate in autumn. Flow cytometric sorting of intensely FLA-laminarin stained cells with subsequent taxonomic identification through 16S rRNA sequencing and fluorescence in situ hybridization revealed a contribution of the verrucomicrobial Pedosphaeraceae to fast uptake of laminarin in summer. Bulk community analysis from that time did not hint at the contribution of these bacteria to polysaccharide turnover, implying that bulk analysis alone can lead to a misestimation of polysaccharide turnover. In the third chapter, we used sensitive radiotracer incubation experiments with amino acids at ambient picomolar concentrations to measure the growth and metabolic activity of a deep-ocean bacterioplankton community in the subtropical North Atlantic. Flow cytometry was proven to be a central tool in the combination of different techniques for a targeted linkage of bacterial identity to metabolic activity for selected bacteria from a complex environmental community. The investigation of polysaccharide and amino acid utilization reveals a new perspective on varying roles played by specific members of complex communities, advances our understanding of heterotrophic organic matter utilization, and provides further insight to their contributions to global biogeochemical cycles.
- Published
- 2020
- Full Text
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