| 1. |
- Smith, Heidi J., et al.
(author)
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Biofilms on glacial surfaces : hotspots for biological activity
- 2016
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In: npj Biofilms and Microbiomes. - : Springer Science and Business Media LLC. - 2055-5008. ; 2
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Journal article (peer-reviewed)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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| 2. |
- Ahmerkamp, Soeren, et al.
(author)
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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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In: CELL REPORTS METHODS. - : Elsevier. - 2667-2375. ; 2:5
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Journal article (peer-reviewed)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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| 3. |
- Foster, Rachel Ann, et al.
(author)
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The rate and fate of N2 and C fixation by marine diatom-diazotroph symbioses
- 2021
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In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370.
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Journal article (peer-reviewed)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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| 4. |
- Holtappels, Moritz, et al.
(author)
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Measurement and interpretation of solute concentration gradients in the benthic boundary layer
- 2011
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In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 9, s. 1-13
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Journal article (peer-reviewed)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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| 5. |
- Klawonn, Isabell, et al.
(author)
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Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea)
- 2016
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920 .- 1758-2229. ; 18:12, s. 4596-4609
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Journal article (peer-reviewed)abstract
- We analysed N2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N2-fixation in surface waters of the Northern Baltic Proper. N2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N2-fixation was 8-fold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N2-fixation. At the coastal station, the cell-specific C- to N2-fixation ratio was below the cellular C:N ratio, i.e., N2 was assimilated in excess to C-fixation, whereas the C- to N2-fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N2-fixation assays in aquatic environments.
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| 6. |
- Klawonn, Isabell, et al.
(author)
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Untangling hidden nutrient dynamics : rapid ammonium cycling and single-cell ammonium assimilation in marine plankton communities
- 2019
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In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 13:8, s. 1960-1974
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Journal article (peer-reviewed)abstract
- Ammonium is a central nutrient in aquatic systems. Yet, cell-specific ammonium assimilation among diverse functional plankton is poorly documented in field communities. Combining stable-isotope incubations (15N-ammonium, 15N2 and 13C-bicarbonate) with secondary-ion mass spectrometry, we quantified bulk ammonium dynamics, N2-fixation and carbon (C) fixation, as well as single-cell ammonium assimilation and C-fixation within plankton communities in nitrogen (N)-depleted surface waters during summer in the Baltic Sea. Ammonium production resulted from regenerated (≥91%) and new production (N2-fixation, ≤9%), supporting primary production by 78–97 and 2–16%, respectively. Ammonium was produced and consumed at balanced rates, and rapidly recycled within 1 h, as shown previously, facilitating an efficient ammonium transfer within plankton communities. N2-fixing cyanobacteria poorly assimilated ammonium, whereas heterotrophic bacteria and picocyanobacteria accounted for its highest consumption (~20 and ~20–40%, respectively). Surprisingly, ammonium assimilation and C-fixation were similarly fast for picocyanobacteria (non-N2-fixing Synechococcus) and large diatoms (Chaetoceros). Yet, the population biomass was high for Synechococcus but low for Chaetoceros. Hence, autotrophic picocyanobacteria and heterotrophic bacteria, with their high single-cell assimilation rates and dominating population biomass, competed for the same nutrient source and drove rapid ammonium dynamics in N-depleted marine waters.
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| 7. |
- Ploug, Helle, et al.
(author)
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Carbon and nitrogen fluxes associated with the cyanobacterium Aphanizomenon sp. in the Baltic Sea
- 2010
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In: The ISME journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:9, s. 1215-1223
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Journal article (peer-reviewed)abstract
- Carbon and nitrogen fluxes in Aphanizomenon sp. colonies in the Baltic Sea were measured using a combination of microsensors, stable isotopes, mass spectrometry, and nanoscale secondary ion mass spectrometry (nanoSIMS). Cell numbers varied between 956 and 33 000 in colonies ranging in volume between 1.4 x 10(-4) and 230 x 10(-4) mm(-3). The high cell content and their productivity resulted in steep O-2 gradients at the colony-water interface as measured with an O-2 microsensor. Colonies were highly autotrophic communities with few heterotrophic bacteria attached to the filaments. Volumetric gross photosynthesis in colonies was 78 nmol O-2 mm(-3) h(-1). Net photosynthesis was 64 nmol O-2 mm(-3) h(-1), and dark respiration was on average 15 nmol O-2 mm(-3) h(-1) or 16% of gross photosynthesis. These volumetric photosynthesis rates belong to the highest measured in aquatic systems. The average cell-specific net carbon-fixation rate was 38 and 40 fmol C cell(-1) h(-1) measured by microsensors and by using stable isotopes in combination with mass spectrometry and nanoSIMS, respectively. In light, the net C:N fixation ratio of individual cells was 7.3 +/- 3.4. Transfer of fixed N-2 from heterocysts to vegetative cells was fast, but up to 35% of the gross N-2 fixation in light was released as ammonium into the surrounding water. Calculations based on a daily cycle showed a net C: N fixation ratio of 5.3. Only 16% of the bulk N-2 fixation in dark was detected in Aphanizomenon sp. Hence, other organisms appeared to dominate N-2 fixation and NH4+ release during darkness.
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| 8. |
- Ploug, Helle, et al.
(author)
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Carbon, nitrogen and O(2) fluxes associated with the cyanobacterium Nodularia spumigena in the Baltic Sea
- 2011
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In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 5:9, s. 1549-1558
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Journal article (peer-reviewed)abstract
- Photosynthesis, respiration, N(2) fixation and ammonium release were studied directly in Nodularia spumigena during a bloom in the Baltic Sea using a combination of microsensors, stable isotope tracer experiments combined with nanoscale secondary ion mass spectrometry (nanoSIMS) and fluorometry. Cell-specific net C-and N(2)-fixation rates by N. spumigena were 81.6 +/- 6.7 and 11.4 +/- 0.9 fmol N per cell per h, respectively. During light, the net C: N fixation ratio was 8.0 +/- 0.8. During darkness, carbon fixation was not detectable, but N(2) fixation was 5.4 +/- 0.4 fmol N per cell per h. Net photosynthesis varied between 0.34 and 250 nmol O(2) h(-1) in colonies with diameters ranging between 0.13 and 5.0 mm, and it reached the theoretical upper limit set by diffusion of dissolved inorganic carbon to colonies (>1 mm). Dark respiration of the same colonies varied between 0.038 and 87 nmol O(2) h (1), and it reached the limit set by O(2) diffusion from the surrounding water to colonies (>1 mm). N(2) fixation associated with N. spumigena colonies (41mm) comprised on average 18% of the total N(2) fixation in the bulk water. Net NH(4)(+) release in colonies equaled 8-33% of the estimated gross N(2) fixation during photosynthesis. NH(4)(+) concentrations within light-exposed colonies, modeled from measured net NH(4)(+) release rates, were 60-fold higher than that of the bulk. Hence, N. spumigena colonies comprise highly productive microenvironments and an attractive NH(4)(+) microenvironment to be utilized by other (micro) organisms in the Baltic Sea where dissolved inorganic nitrogen is limiting growth.
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| 9. |
- Svedén, Jennie B., et al.
(author)
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High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp at low temperatures in the Baltic Sea
- 2015
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 91:12
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Journal article (peer-reviewed)abstract
- Aphanizomenon is a widespread genus of nitrogen (N-2)-fixing cyanobacteria in lakes and estuaries, accounting for a large fraction of the summer N-2-fixation in the Baltic Sea. However, information about its cell-specific carbon (C)- and N-2-fixation rates in the early growth season has not previously been reported. We combined various methods to study N-2-fixation, photosynthesis and respiration in field-sampled Baltic Sea Aphanizomenon sp. during early summer at 10 degrees C. Stable isotope incubations at in situ light intensities during 24 h combined with cell-specific secondary ion mass spectrometry showed an average net N-2-fixation rate of 55 fmol N cell(-1) day(-1). Dark net N-2-fixation rates over a course of 12 h were 20% of those measured in light. C-fixation, but not N-2-fixation, was inhibited by high ambient light intensities during daytime. Consequently, the C: N fixation ratio varied substantially over the diel cycle. C-and N-2-fixation rates were comparable to those reported for Aphanizomenon sp. in August at 19 degrees C, using the same methods. High respiration rates (23% of gross photosynthesis) were measured with C-14-incubations and O-2-microsensors, and presumably reflect the energy needed for high N-2-fixation rates. Hence, Aphanizomenon sp. is an important contributor to N-2-fixation at low in situ temperatures in the early growth season.
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| 10. |
- Eichner, Meri, et al.
(author)
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Chemical microenvironments and single-cell carbon and nitrogen uptake in field-collected colonies of Trichodesmium under different pCO2
- 2017
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In: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 11, s. 1305-1317
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Journal article (peer-reviewed)abstract
- © 2017 The Author(s)Gradients of oxygen (O2) and pH, as well as small-scale fluxes of carbon (C), nitrogen (N) and O2 were investigated under different partial pressures of carbon dioxide (pCO2) in field-collected colonies of the marine dinitrogen (N2)-fixing cyanobacterium Trichodesmium. Microsensor measurements indicated that cells within colonies experienced large fluctuations in O2, pH and CO2 concentrations over a day–night cycle. O2 concentrations varied with light intensity and time of day, yet colonies exposed to light were supersaturated with O2 (up to ~200%) throughout the light period and anoxia was not detected. Alternating between light and dark conditions caused a variation in pH levels by on average 0.5 units (equivalent to 15nmoll-1 proton concentration). Single-cell analyses of C and N assimilation using secondary ion mass spectrometry (SIMS; large geometry SIMS and nanoscale SIMS) revealed high variability in metabolic activity of single cells and trichomes of Trichodesmium, and indicated transfer of C and N to colony-associated non-photosynthetic bacteria. Neither O2 fluxes nor C fixation by Trichodesmium were significantly influenced by short-term incubations under different pCO2 levels, whereas N2 fixation increased with increasing pCO2. The large range of metabolic rates observed at the single-cell level may reflect a response by colony-forming microbial populations to highly variable microenvironments.The ISME Journal advance online publication, 11 April 2017; doi:10.1038/ismej.2017.15.
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