| 1. |
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| 2. |
- Schmid, M. C., et al.
(författare)
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Anaerobic ammonium-oxidizing bacteria in marine environments: widespread occurrence but low diversity
- 2007
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 9:6, s. 1476-1484
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory and field studies have indicated that anaerobic ammonium oxidation (anammox) is an important process in the marine nitrogen cycle. In this study 11 additional anoxic marine sediment and water column samples were studied to substantiate this claim. In a combined approach using the molecular methods, polymerase chain reaction (PCR), qualitative and quantitative fluorescence in situ hybridization (FISH), as well as N-15 stable isotope activity measurements, it was shown that anammox bacteria were present and active in all samples investigated. The anammox activity measured in the sediment samples ranged from 0.08 fmol cell(-1) day(-1) N-2 in the Golfo Dulce (Pacific Ocean, Costa Rica) sediment to 0.98 fmol cell(-1) day(-1) N-2 in the Gullmarsfjorden (North Sea, Sweden) sediment. The percentage of anammox cell of the total population (stained with DAPI) as assessed by quantitative FISH was highest in the Barents Sea (9% +/- 4%) and in most of the samples well over 2%. Fluorescence in situ hybridization and phylogenetic analysis of the PCR products derived from the marine samples indicated the exclusive presence of members of the Candidatus 'Scalindua' genus. This study showed the ubiquitous presence of anammox bacteria in anoxic marine ecosystems, supporting previous observations on the importance of anammox for N cycling in marine environments.
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| 3. |
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| 4. |
- Smith, H. J., et al.
(författare)
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Microbial formation of labile organic carbon in Antarctic glacial environments
- 2017
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 10:5, s. 356-359
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Tidskriftsartikel (refereegranskat)abstract
- Roughly six petagrams of organic carbon are stored within ice worldwide. This organic carbon is thought to be of old age and highly bioavailable. Along with storage of ancient and new atmospherically deposited organic carbon, microorganisms may contribute substantially to the glacial organic carbon pool. Models of glacial microbial carbon cycling vary from net respiration to net carbon fixation. Supraglacial streams have not been considered in models although they are amongst the largest ecosystems on most glaciers and are inhabited by diverse microbial communities. Here we investigate the biogeochemical sequence of organic carbon production and uptake in an Antarctic supraglacial stream in the McMurdo Dry Valleys using nanometre-scale secondary ion mass spectrometry, fluorescence spectroscopy, stable isotope analysis and incubation experiments. We find that heterotrophic production relies on highly labile organic carbon freshly derived from photosynthetic bacteria rather than legacy organic carbon. Exudates from primary production were utilized by heterotrophs within 24 h, and supported bacterial growth demands. The tight coupling of microbially released organic carbon and rapid uptake by heterotrophs suggests a dynamic local carbon cycle. Moreover, as temperatures increase there is the potential for positive feedback between glacial melt and microbial transformations of organic carbon.
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| 5. |
- Smith, Heidi J., et al.
(författare)
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Biofilms on glacial surfaces : hotspots for biological activity
- 2016
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Ingår i: npj Biofilms and Microbiomes. - : Springer Science and Business Media LLC. - 2055-5008. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Glaciers are important constituents in the Earth's hydrological and carbon cycles, with predicted warming leading to increases in glacial melt and the transport of nutrients to adjacent and downstream aquatic ecosystems. Microbial activity on glacial surfaces has been linked to the biological darkening of cryoconite particles, affecting albedo and increased melt. This phenomenon, however, has only been demonstrated for alpine glaciers and the Greenland Ice Sheet, excluding Antarctica. In this study, we show via confocal laser scanning microscopy that microbial communities on glacial surfaces in Antarctica persist in biofilms. Overall, similar to 35% of the cryoconite sediment surfaces were covered by biofilm. Nanoscale scale secondary ion mass spectrometry measured significant enrichment of C-13 and N-15 above background in both Bacteroidetes and filamentous cyanobacteria (i.e., Oscillatoria) when incubated in the presence of C-13-NaHCO3 and (NH4)-N-15. This transfer of newly synthesised organic compounds was dependent on the distance of heterotrophic Bacteroidetes from filamentous Oscillatoria. We conclude that the spatial organisation within these biofilms promotes efficient transfer and cycling of nutrients. Further, these results support the hypothesis that biofilm formation leads to the accumulation of organic matter on cryoconite minerals, which could influence the surface albedo of glaciers.
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| 6. |
- Adam, Birgit, et al.
(författare)
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N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community
- 2016
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 10:2, s. 450-459
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the role of N2-fixation by the colony-forming cyanobacterium, Aphanizomenon spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. When incubated with 15N2, Aphanizomenon spp. showed a strong 15N-enrichment implying substantial 15N2-fixation. Intriguingly, Aphanizomenon did not assimilate tracers of 15NH4+ from the surrounding water. These findings are in line with model calculations that confirmed a negligible N-source by diffusion-limited NH4+ fluxes to Aphanizomenon colonies at low bulk concentrations (<250 nm) as compared with N2-fixation within colonies. No N2-fixation was detected in autotrophic microorganisms <5 mum, which relied on NH4+ uptake from the surrounding water. Aphanizomenon released about 50% of its newly fixed N2 as NH4+. However, NH4+ did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (Chaetoceros sp.) and copepods with a turnover time of ~5 h. We provide direct quantitative evidence that colony-forming Aphanizomenon releases about half of its recently fixed N2 as NH4+, which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N2-fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.
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| 7. |
- Ahmerkamp, Soeren, et al.
(författare)
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Simultaneous visualization of flow fields and oxygen concentrations to unravel transport and metabolic processes in biological systems
- 2022
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Ingår i: CELL REPORTS METHODS. - : Elsevier. - 2667-2375. ; 2:5
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Tidskriftsartikel (refereegranskat)abstract
- From individual cells to whole organisms, O-2 transport unfolds across micrometer- tomillimeter-length scales and can change within milliseconds in response to fluid flows and organismal behavior. The spatiotemporal complexity of these processes makes the accurate assessment of O-2 dynamics via currently availablemethods difficult or unreliable. Here, we present "sensPIV,'' a method to simultaneously measure O-2 concentrations and flow fields. By tracking O-2-sensitive microparticles in flow using imaging technologies that allow for instantaneous referencing, wemeasuredO(2) transportwithin (1) microfluidic devices, (2) sinkingmodel aggregates, and (3) complex colony-forming corals. Through the use of sensPIV, we find that corals use ciliarymovement to link zones of photosynthetic O-2 production to zones of O-2 consumption. SensPIV can potentially be extendable to study flow-organism interactions across many life-science and engineering applications.
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| 8. |
- Foster, Rachel Ann, et al.
(författare)
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The rate and fate of N2 and C fixation by marine diatom-diazotroph symbioses
- 2021
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370.
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Tidskriftsartikel (refereegranskat)abstract
- N2 fixation constitutes an important new nitrogen source in the open sea. One group of filamentous N2 fixing cyanobacteria (Richelia intracellularis, hereafter Richelia) form symbiosis with a few genera of diatoms. High rates of N2 fixation and carbon (C) fixation have been measured in the presence of diatom-Richelia symbioses. However, it is unknown how partners coordinate C fixation and how the symbiont sustains high rates of N2 fixation. Here, both the N2 and C fixation in wild diatom-Richelia populations are reported. Inhibitor experiments designed to inhibit host photosynthesis, resulted in lower estimated growth and depressed C and N2 fixation, suggesting that despite the symbionts ability to fix their own C, they must still rely on their respective hosts for C. Single cell analysis indicated that up to 22% of assimilated C in the symbiont is derived from the host, whereas 78–91% of the host N is supplied from their symbionts. A size-dependent relationship is identified where larger cells have higher N2 and C fixation, and only N2 fixation was light dependent. Using the single cell measures, the N-rich phycosphere surrounding these symbioses was estimated and contributes directly and rapidly to the surface ocean rather than the mesopelagic, even at high estimated sinking velocities (<10 m d−1). Several eco-physiological parameters necessary for incorporating symbiotic N2 fixing populations into larger basin scale biogeochemical models (i.e., N and C cycles) are provided.
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| 9. |
- Heller, T., et al.
(författare)
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Plasma concentrations of mycophenolic acid acyl glucuronide are not associated with diarrhea in renal transplant recipients
- 2007
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Ingår i: American Journal of Transplantation. - : Elsevier BV. - 1600-6135 .- 1600-6143. ; 7:7, s. 1822-1831
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to determine whether plasma concentrations of the acyl (AcMPAG) and phenolic (MPAG) glucuronide metabolites of mycophenolic acid (MPA) were related to diarrhoea in renal transplant patients on mycophenolate mofetil (MMF) with cyclosporine (CsA) or tacrolimus (TCL). Blood samples (0, 30, 120 min) were taken at days 3, 10, week 4, months 3, 6 and 12 for determination of MPA, MPAG and AcMPAG. MPA-AUC was estimated using validated algorithms. Two hour AUCs were calculated for MPAG and AcMPAG. Immunosuppressive therapy consisted of CsA/MMF (n= 110) and of TCL/MMF (n= 180). In 70/290 (24%) patients 86 episodes of diarrhoea were recorded during 12 months. Significantly more patients on TCL (31.1%) suffered from diarrhea compared to CsA (12.7%). MMF dose, MPA-AUC and the 2 h AUCs of MPAG and AcMPAG did not differ between patients with and without diarrhoea. Plasma AcMPAG and MPAG concentrations were substantially higher in patients on CsA compared with TCL, while MPA-AUC was lower in the former group. These data support the concept that CsA inhibits the biliary excretion of MPAG and AcMPAG, thereby potentially reducing the risk of intestinal injury through enterohepatic recycling of MPA and its metabolites.
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| 10. |
- Holtappels, Moritz, et al.
(författare)
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Measurement and interpretation of solute concentration gradients in the benthic boundary layer
- 2011
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Ingår i: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 9, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- The coastal ocean is characterized by high exchange rates of organic matter, oxygen, and nutrients between the sediment and the water column. The solutes that are exchanged between the sediment and the overlying water column are transported across the benthic boundary layer (BBL) by means of turbulent diffusion. Thus, solute concentration gradients in the BBL contain valuable information about the respective fluxes. In this study, we present the instrumentation and sampling strategies to measure oxygen and nutrient concentration gradients in the BBL. We provide the theoretical background and the calculation procedure to derive ratios of nutrient and oxygen fluxes from these concentration gradients. The noninvasive approach is illustrated at two sampling sites in the western Baltic Sea where nutrient and oxygen concentration gradients of up to 5 and 30 mu M m(-1), respectively, were measured. Nutrient and oxygen flux ratios were used to establish a nitrogen flux balance between sediment and water column indicating that 20% and 50% of the mineralized nitrogen left the sediment in form of N(2) (station A and B, respectively). The results are supported by sediment incubation experiments of intact sediment cores, measuring denitrification rates, and oxygen uptake. The presented flux ratio approach is applicable without knowledge of turbulent diffusivities in the BBL and is, therefore, unaffected by non-steady-state current velocities and diffusivities.
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