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  • 1
    Electronic Resource
    Electronic Resource
    Effectiveness of CSE to counterstain particles and dead bacterial cells with permeabilised membranes: application to viability assessment in waters (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 178 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The CSE dye (Chemunex, Maisons-Alfort, France) was combined with an activity marker to improve bacterial activity assessment in natural waters. Its effectiveness to counterstain dead cells with permeabilised membranes was investigated on live and dead cells of a variety of strains from collections or isolated from the natural environment. Cells were killed by heat treatment. For all strains tested, the fluorescent dye showed an intense staining of killed cells having permeabilised membranes while no significant signal was detected when applied to live cells. Furthermore, the CSE dye had no toxicity on viable cells. Then, CSE was combined with the ChemChrome V6 dye (Chemunex) to assess the activity of bacterial cells in different waters. Both fluorescences were analysed simultaneously by solid-phase cytometry. The active cell counts were sometimes lower when both dyes were combined suggesting that CSE was able to counterstain cells having a residual esterase activity and compromised membranes. These cells were subtracted from the active cell counts determined with ChemChrome V6. In most samples, active cell counts were congruent with those determined by the direct viable count method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb08680.x
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    Paper (German National Licenses)
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  • 2
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    Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used (2021)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Ectoenzymatic activity, prokaryotic heterotrophic abundances and production were determined in the Mediterranean Sea. Sampling was carried out in the sub-surface, the deep chlorophyll maximum layer (DCM), the core of the Levantine intermediate waters and in the deeper part of the mesopelagic layers. Michaelis–Menten kinetics were assessed using a large range of concentrations of fluorogenic substrates (0.025 to 50 µM). As a consequence, Km (Michaelis–Menten half-saturation constant) and Vm (maximum hydrolysis velocity) parameters were determined for both low- and high-affinity enzymes for alkaline phosphatase, aminopeptidase (LAP) and β-glucosidase (βGLU). Based on the constant derived from the high-LAP-affinity enzyme (0.025–1 µM substrate concentration range), in situ hydrolysis of N proteins contributed 48 % ± 30 % to the heterotrophic bacterial nitrogen demand within the epipelagic layers and 180 % ± 154 % in the Levantine intermediate waters and the upper part of the mesopelagic layers. The LAP hydrolysis rate was higher than bacterial N demand only within the deeper layer and only when considering the high-affinity enzyme. Based on a 10 % bacterial growth efficiency, the cumulative hydrolysis rates of C proteins and C polysaccharides contributed on average 2.5 % ± 1.3  % to the heterotrophic bacterial carbon demand in the epipelagic layers sampled (sub-surface and DCM). This study clearly reveals potential biases in current and past interpretations of the kinetic parameters for the three enzymes tested based on the fluorogenic-substrate concentration used. In particular, the LAP / βGLU enzymatic ratios and some of the depth-related trends differed between the use of high and low concentrations of fluorogenic substrates.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Dissolved organic matter released by two marine heterotrophic bacterial strains and its bioavailability for natural prokaryotic communities (2021)
    Wiley | Society for Applied Microbiology
    Details
    Publication Date: 2024-02-07
    Description: Marine heterotrophic prokaryotes (HP) play a key role in organic matter processing in the ocean; however, the view of HP as dissolved organic matter (DOM) sources remains underexplored. In this study, we quantified and optically characterized the DOM produced by two single marine bacterial strains. We then tested the availability of these DOM sources to in situ Mediterranean Sea HP communities. Two bacterial strains were used: Photobacterium angustum (a copiotrophic gammaproteobacterium) and Sphingopyxis alaskensis (an oligotrophic alphaproteobacterium). When cultivated on glucose as the sole carbon source, the two strains released from 7% to 23% of initial glucose as bacterial derived DOM (B-DOM), the quality of which (as enrichment in humic or protein-like substances) differed between strains. B-DOM induced significant growth and carbon consumption of natural HP communities, suggesting that it was partly labile. However, B-DOM consistently promoted lower prokaryotic growth efficiencies than in situ DOM. In addition, B-DOM changed HP exoenzymatic activities, enhancing aminopeptidase activity when degrading P. angustum DOM, and alkaline phosphatase activity when using S. alaskensis DOM, and promoted differences in HP diversity and composition. DOM produced by HP affects in situ prokaryotic metabolism and diversity, thus changing the pathways for DOM cycling (e.g. respiration over biomass production) in the ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Dynamics of inorganic and organic phosphorous substrate utilization by extant microbial populations in the North-West Mediterranean Sea (2014)
    In:  EPIC32014 Ocean Sciences Meeting 2014, Honolulu, Hawaii, USA, 2014-02-23-2014-02-28
    Details
    Publication Date: 2016-04-07
    Description: Phosphorous is a proximal limiting nutrient in certain oceanic regions. We studied the seasonal dynamics of inorganic and organic phosphorous utilisation over a one-year period (2012) in the NW Mediterranean. 33P-labelled bioassays and flow sorting experiments were combined to address the seasonality in turnover, concentration and uptake rates of phosphate, ATP and DNA by dominant microbial groups. In parallel, 454 pyrosequencing was conducted to link changes in phosphorus substrate utilisation to prokaryotic community composition. Although increases in organic phosphorous utilisation correspond to short phosphate turnover times, phosphate uptake also increases to the extent that the majority of community phosphorous flux is channelled through the inorganic pool, irrespective of the degree of phosphate limitation. Bacteria maintain a fairly uniform pattern phosphorous substrate utilisation throughout the year. In contrast, Synechococcus and Eukaryotic populations rely increasingly on organic phosphorous substrates during times of extreme phosphate limitation. Sequencing data is employed to elucidate whether the observed patterns in substrate utilisation correspond to metabolic flexibility of a dominant ecotype or community dynamics of Synechococcus ecotypes adapted to different phosphorous acquisition strategies.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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    PAPER (OA)
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