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  • 1
    Online Resource
    Online Resource
    The influence of oxygen concentration on bacterial turnover of dissolved organic matter (2015)
    Kiel
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (102 Blatt = 7 MB) , Illustrationen, Diagramme, Karten
    URL: http://oceanrep.geomar.de/40382/
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
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    On the effect of low oxygen concentrations on bacterial degradation of sinking particles (2017)
    Nature Research
    In:  Scientific Reports, 7 (1). Art. No. 16722.
    Details
    Publication Date: 2020-06-18
    Description: In marine oxygen (O2) minimum zones (OMZs), the transfer of particulate organic carbon (POC) to depth via the biological carbon pump might be enhanced as a result of slower remineralisation under lower dissolved O2 concentrations (DO). In parallel, nitrogen (N) loss to the atmosphere through microbial processes, such as denitrification and anammox, is directly linked to particulate nitrogen (PN) export. However it is unclear (1) whether DO is the only factor that potentially enhances POC transfer in OMZs, and (2) if particle fluxes are sufficient to support observed N loss rates. We performed a degradation experiment on sinking particles collected from the Baltic Sea, where anoxic zones are observed. Sinking material was harvested using surface-tethered sediment traps and subsequently incubated in darkness at different DO levels, including severe suboxia (〈0.5 mg l−1 DO). Our results show that DO plays a role in regulating POC and PN degradation rates. POC(PN) degradation was reduced by approximately 100% from the high to low DO to the lowest DO. The amount of NH4+ produced from the pool of remineralising organic N matched estimations of NH4+ anammox requirements during our experiment. This anammox was likely fueled by DON degradation rather than PON degradation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41598-017-16903-3
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Bacterial Activity and Organic Matter Turnover in Oxygen Deficient Waters of the Baltic Sea (2016)
    In:  [Poster] In: Ocean Sciences Meeting 2016, 21.-26.02.2016, New Orleans, USA .
    Details
    Publication Date: 2019-09-23
    Description: The Baltic Sea is an enclosed marine system that suffers from expanding zones of oxygen deficiency due to limited ventilation by the episodic inflow of oxygenated North Sea water combined with high anthropogenic nutrient loads. In particular coastal areas are strongly influenced by eutrophication that leads to enhanced microbial oxygen consumption and sporadic anoxia even at shallow sites. It has been shown that oxygen availability is a powerful determinant of the taxonomic composition of prokaryotic communities in deep waters of the Baltic Sea. However, it remains unclear if community changes in response to low oxygen impact carbon remineralization or if functional redundancy prevents effects on major biogeochemical processes driven by bacterial activity. Our study includes monthly samplings at a coastal time series station over three annual cycles with recurring anoxic periods in late summer. Furthermore, sampling was accomplished in the deep Gotland Basin, where a permanent pycnocline prevents vertical mixing. We determined rates of extracellular glucosidase, aminopeptidase and phosphatase, as well as bacterial protein production using fluorescent and radioactive labelled substrate analogues, respectively. The rate measurements were combined with the analysis of organic matter concentration and composition by different analytical tools. Field data and experimental work show that enzymatic polymer hydrolysis, bacterial biomass production and growth rates in oxygen deficient waters of the Baltic Sea are not inherently lower than in oxic waters. Instead, results reveal that the reactivity of organic carbon and the availability of inorganic nutrients are more powerful constraints on organic matter turnover in oxygen deficient zones of the Baltic Sea. Our results imply that oxygen availability alone is not the decisive factor for heterotrophic bacterial activity in deep waters, instead it is part of a multiple environmental control of carbon remineralization.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 4
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    The influence of oxygen concentration on bacterial turnover of dissolved organic matter (2015)
    In:  (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 82 + 1 CD pp
    Details
    Publication Date: 2019-09-23
    Keywords: Course of study: MSc Biological Oceanography
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
  • 5
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    Uncovering the role of oxygen on organic carbon cycling: Insights from a continuous culture study with a facultative anaerobic bacterioplankton species (Shewanella baltica) (2024)
    Frontiers
    Details
    Publication Date: 2024-04-15
    Description: Deoxygenation is tied to organic carbon (Corg) supply and utilization in marine systems. Under oxygen-depletion, bacteria maintain respiration using alternative electron acceptors such as nitrate. Since anaerobic respiration's energy yield is lower, Corg remineralization may be reduced and its residence time increased. We investigated the influence of oxygen and alternative electron acceptors' availability on Corg cycling by heterotrophic bacteria during a continuous culture experiment with Shewanella baltica, a facultative anaerobic γ-Proteobacteria in the Baltic Sea. We tested six different oxygen levels, from suboxic (〈5 µmol L-1 ) to fully oxic conditions, using media (salinity=14 g L-1 ) supplied with high (HighN) or low (LowN) inorganic nitrogen concentrations relative to glucose as labile Corg source. Our results show that suboxia limited DOC (glucose) uptake and cell growth only under LowN, while higher availability of alternative electron acceptors seemingly compensated oxygen limitation under HighN. N-loss was observed under suboxia in both nitrogen treatments. Under HighN, N-loss was highest and a C:N loss ratio of ~2.0 indicated that Corg was remineralized via denitrification. Under LowN, the C:N loss ratio under suboxia was higher (~5.5), suggesting dominance of other anaerobic respiration pathways, such as dissimilatory nitrate reduction to ammonium (DNRA). Bacterial growth efficiency was independent of oxygen concentration but higher under LowN (34±3.0%) than HighN (26±1.6%). Oxygen concentration also affected dissolved organic matter (DOM) cycling. Under oxic conditions, the release of dissolved combined carbohydrates was enhanced, and the amino acid-based degradation index (DI) pointed to more diagenetically altered DOM. Our results suggest bacterial Corg uptake in low-oxygen systems dominated by S. baltica can be limited by oxygen but compensated by high nitrate availability. Hence, suboxia diminishes Corg remineralisation only when alternative electron acceptors are lacking. Under high nitrate:Corg supply, denitrification leads to a higher N:C loss ratio, potentially counteracting eutrophication in the long run. Low nitrate:Corg supply may favour other anaerobic respiration pathways like DNRA, which sustains labile nitrogen in the system, potentially intensifying the cycle of eutrophication. Going forward, it will be crucial to establish the validity of our findings for S. baltica in natural systems with diverse organic substrates and microbial consortia.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Potential role of oxygen and inorganic nutrients on microbial carbon turnover in the Baltic Sea (2019)
    Inter Research
    In:  Aquatic Microbial Ecology, 83 . pp. 95-108.
    Details
    Publication Date: 2022-01-31
    Description: Oxygen (O2) deficiency and nutrient concentrations in marine systems are impacting organisms from microbes to higher trophic levels. In coastal and enclosed seas, O2 deficiency is often related to eutrophication and high degradation rates of organic matter. To investigate the impact of O2 concentration on bacterial growth and the turnover of organic matter, we conducted multifactorial batch experiments with natural microbial communities of the central Baltic Sea. Water was collected from suboxic (〈5 µmol L -1) depths in the Gotland Basin during June 2015. Samples were kept for four days under fully oxygenated and low O2 conditions (mean: 34 µmol L-1 O2), with or without nutrient (ammonium, phosphate, nitrate) and labile carbon (glucose) amendments. We measured bacterial abundance, bacterial heterotrophic production, extracellular enzyme rates (leucine-aminopeptidase) and changes in dissolved and particulate organic carbon concentrations. Our results show that the bacterial turnover of organic matter was limited by nutrients under both oxic and low O2 conditions. In nutrient and glucose replete treatments, low O2 concentrations significantly reduced the net uptake of dissolved organic carbon and lead to higher accumulation of more labile dissolved organic matter. Our results therewith suggest that the combined effects of eutrophication and deoxygenation on heterotrophic bacterial activity may potentially favor the accumulation of dissolved organic carbon in the Baltic Sea.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/ame01902
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-02-08
    Description: Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotrophic bacterial production (3H leucine incorporation), extracellular enzyme rates (leucine aminopeptidase/β-glucosidase) and bacterial cell abundance for various in situ oxygen concentrations in the water column, including the upper and lower oxycline, of the eastern tropical South Pacific off Peru. Bacterial heterotrophic activity in the suboxic core of the OMZ (at in situ ≤ 5 µmol O2 kg−1) ranged from 0.3 to 281 µmol C m−3 d−1 and was not significantly lower than in waters of 5–60 µmol O2 kg−1. Moreover, bacterial abundance in the OMZ and leucine aminopeptidase activity were significantly higher in suboxic waters compared to waters of 5–60 µmol O2 kg−1, suggesting no impairment of bacterial organic-matter degradation in the core of the OMZ. Nevertheless, high cell-specific bacterial production was observed in samples from oxyclines, and cell-specific extracellular enzyme rates were especially high at the lower oxycline, corroborating earlier findings of highly active and distinct micro-aerobic bacterial communities. To assess the impact of bacterial degradation of dissolved organic matter (DOM) for oxygen loss in the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved organic carbon (DOC) and their microbial uptake within the upper 60 m of the water column. Our data indicate low bacterial growth efficiencies of 1 %–21 % at the upper oxycline, resulting in a high bacterial oxygen demand that can explain up to 33 % of the observed average oxygen loss over depth. Our study therewith shows that microbial degradation of DOM has a considerable share in sustaining the OMZ off Peru.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Climate-Biogeochemistry Interactions in the Tropical Ocean: Data collection and legacy (2021)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: From 2008 through 2019, a comprehensive research project, SFB 754, Climate - Biogeochemistry Interactions in the Tropical Ocean, was funded by the German Research Foundation to investigate the climate-biogeochemistry interactions in the tropical ocean with a particular emphasis on the processes determining the oxygen distribution. During three 4-year long funding phases, a consortium of more than 150 scientists conducted or participated in 34 major research cruises and collected a wealth of physical, biological, chemical, and meteorological data. A common data policy agreed upon at the initiation of the project provided the basis for the open publication of all data. Here we provide an inventory of this unique data set and briefly summarize the various data acquisition and processing methods used.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Dissolved Organic Matter in the Upwelling System off Peru: Imprints of Bacterial Activity and Water Mass Characteristics (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Microbial degradation of dissolved organic matter (DOM) contributes to the formation and preservation of oxygen minimum zones (OMZs) in the ocean, but information on the spatial distribution and molecular composition of DOM in OMZ regions is scarce. We quantified molecular components of DOM that is, dissolved amino acids (DAA) and dissolved combined carbohydrates (DCCHO), in the upwelling region off Peru. We found the highest concentrations of DCCHO in fully oxygenated surface waters steeply declining at shallow depth. The highest DAA concentrations were observed close to the surface also, but attenuation of DAA concentration over depth was less pronounced. Compositional changes of DCCHO were strongest within more oxygenated waters. Compositional changes of DAA were also evident under suboxic conditions (〈5 µmol O2 kg−1) and indicated bacterial peptide degradation. Moreover, specific free amino acids (alanine and threonine) were enhanced within suboxic waters, pointing to a potential production of dissolved organic nitrogen under suboxic conditions. Our results therewith suggest that deoxygenation supports a spatial decoupling of DCCHO and DAA production and degradation dynamics and give new insights to carbon and nitrogen cycling in the OMZ off Peru.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    On the influence of oxygen concentration on the activity and dissolved organic matter turnover of marine bacteria (2021)
    Details
    Publication Date: 2024-02-07
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
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