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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 14 February 2012, Vol.109(7), pp.2412-7
    Description: The spatial organization of biofilms is strongly regulated by chemical cues released by settling organisms. However, the exact nature of these interactions and the repertoire of chemical cues and signals that micro-organisms produce and exude in response to the presence of competitors remain largely unexplored. Biofilms dominated by microalgae often show remarkable, yet unexplained fine-scale patchy variation in species composition. Because this occurs even in absence of abiotic heterogeneity, antagonistic interactions might play a key role. Here we show that a marine benthic diatom produces chemical cues that cause chloroplast bleaching, a reduced photosynthetic efficiency, growth inhibition and massive cell death in naturally co-occurring competing microalgae. Using headspace solid phase microextraction (HS-SPME)-GC-MS, we demonstrate that this diatom exudes a diverse mixture of volatile iodinated and brominated metabolites including the natural product cyanogen bromide (BrCN), which exhibits pronounced allelopathic activity. Toxin production is light-dependent with a short BrCN burst after sunrise. BrCN acts as a short-term signal, leading to daily "cleaning" events around the algae. We show that allelopathic effects are H(2)O(2) dependent and link BrCN production to haloperoxidase activity. This strategy is a highly effective means of biofilm control and may provide an explanation for the poorly understood role of volatile halocarbons from marine algae, which contribute significantly to the atmospheric halocarbon budget.
    Keywords: Biofilms ; Cyanogen Bromide -- Metabolism ; Diatoms -- Metabolism ; Pheromones -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    In: PLoS ONE, 2013, Vol.8(3)
    Description: Marine lytic bacteria can have a substantial effect on phytoplankton and are even capable to terminate blooms of microalgae. The bacterium Kordia algicida was reported to lyse cells of the diatom Skeletonema costatum and several other diatoms by a quorum sensing controlled excretion of proteases. However the diatom Chaetoceros didymus is fully resistant against the bacterial enzymes. We show that the growth curve of this diatom is essentially unaffected by addition of bacterial filtrates that are active against other diatoms. By monitoring proteases from the medium using zymography and fluorescence based activity assays we demonstrate that C. didymus responds to the presence of the lytic bacteria with the induced production of algal proteases. These proteases exhibit a substantially increased activity compared to the bacterial counterparts. The induction is also triggered by signals in the supernatant of a K. algicida culture. Size fractionation shows that only the 〉30 kD fraction of the bacterial exudates acts as an inducing cue. Implications for a potential induced defense of the diatom C. didymus are discussed.
    Keywords: Research Article ; Biology ; Mathematics
    E-ISSN: 1932-6203
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  • 3
    In: PLoS ONE, 2011, Vol.6(6)
    Description: Interactions of planktonic bacteria with primary producers such as diatoms have great impact on plankton population dynamics. Several studies described the detrimental effect of certain bacteria on diatoms but the biochemical nature and the regulation mechanism involved in the production of the active compounds remained often elusive. Here, we investigated the interactions of the algicidal bacterium Kordia algicida with the marine diatoms Skeletonema costatum , Thalassiosira weissflogii , Phaeodactylum tricornutum , and Chaetoceros didymus . Algicidal activity was only observed towards the first three of the tested diatom species while C. didymus proved to be not susceptible. The cell free filtrate and the 〉30 kDa fraction of stationary K. algicida cultures is fully active, suggesting a secreted algicidal principle. The active supernatant from bacterial cultures exhibited high protease activity and inhibition experiments proved that these enzymes are involved in the observed algicidal action of the bacteria. Protease mediated interactions are not controlled by the presence of the alga but dependent on the cell density of the K. algicida culture. We show that protease release is triggered by cell free bacterial filtrates suggesting a quorum sensing dependent excretion mechanism of the algicidal protein. The K. algicida / algae interactions in the plankton are thus host specific and under the control of previously unidentified factors.
    Keywords: Research Article ; Biology ; Chemistry
    E-ISSN: 1932-6203
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  • 4
    Language: English
    In: Metabolomics, 2013, Vol.9(2), pp.349-359
    Description: Chemically mediated interactions are hypothesized to be essential for ecosystem functioning as co-occurring organisms can influence the performance of each other by metabolic means. A metabolomics approach can support a better understanding of such processes but many problems cannot be addressed due to a lack of appropriate co-culturing and sampling strategies. This is particularly true for planktonic organisms that live in complex but very dilute communities in the open water. Here we present a co-culturing device that allows culturing of microalgae and bacteria that are physically separated but can exchange dissolved or colloidal chemical signals. Identical growth conditions for both partners as well as high metabolite diffusion rates between the culturing chambers are ensured. This setup allowed us to perform a metabolomic survey of the effect of the bacterium Dinoroseobacter shibae on the diatom Thalassiosira pseudonana. GC–MS measurements revealed a pronounced influence of the bacterium on the metabolic profile of T. pseudonana cells with especially intracellular amino acids being up-regulated in co-cultures. Despite the influence on diatom metabolism, the bacterium has little influence on the growth of the algae. This might indicate that the observed metabolic changes represent an adaptive response of the diatoms. Such interactions might be crucial for metabolic fluxes within plankton communities.
    Keywords: Diatom ; Metabolomics ; Plankton interactions ; Co-culture ; Thalassiosira pseudonana
    ISSN: 1573-3882
    E-ISSN: 1573-3890
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  • 5
    In: Natural Product Reports, 2011, Vol.28(2), pp.186-195
    Description: Covering: up to August 2010 Marine organisms are an important source of volatile halogenated natural products. Marine algae, in particular, contribute significantly to the global budget of halogenated hydrocarbons that play an important role in climate functioning. However, despite the large amounts of halogenated metabolites from algae, we know relatively little about their function in the producing organism. In this Highlight, we discuss the current knowledge of volatile halogenated compounds from algae, with a focus on biosynthesis, algal physiology and chemical ecology. We also briefly discuss geochemical aspects arising from the release of halogenated natural products from micro- and macroalgae.
    Keywords: Halogenated Hydrocarbons ; Volatiles ; Climate ; Marine Organisms ; Metabolites ; Natural Products ; Algae ; Algae ; Biochemistry;
    ISSN: 0265-0568
    E-ISSN: 1460-4752
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  • 6
    Language: English
    In: R & D, 2017, Vol.59(1), p.24(2)
    Keywords: High Performance Liquid Chromatography – Methods ; High Performance Liquid Chromatography – Technology Application ; Scientific Software – Usage
    ISSN: 0746-9179
    Source: Cengage Learning, Inc.
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  • 7
    In: European Company and Financial Law Review, 2010, Vol.7(1), pp.81-115
    Description: Derivative actions, i. e. the ability of shareholders to bring proceedings to enforce a cause of action vested in the company, may be considered an essential constituent of almost every corporate governance system. Derivative action litigation has been commonly used in both common law and civil law systems as a means to monitor corporate management and to protect minority shareholders' interests. However, to be effective as a minority shareholder protection device, it is key that derivative action legislation strikes the right balance to ensure that both shareholder incentives and effective safeguards are in place. Indeed, if the pendulum swings too far in any direction, derivative actions may either be a dull corporate governance sword or an open floodgate for vexatious shareholder litigation. In this article, the author undertakes to explore this balance on a comparative basis involving English and German corporate law and argues that despite obvious conceptual similarities in both jurisdictions the pendulum swings different ways.
    Keywords: Stockholders -- Laws, Regulations And Rules ; Corporation Law -- Laws, Regulations And Rules ; Corporate Governance -- Laws, Regulations And Rules;
    ISSN: 1613-2548
    E-ISSN: 1613-2556
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  • 8
    Language: English
    In: ChemInform, 05/24/2011, Vol.42(21), pp.no-no
    ISSN: ChemInform
    E-ISSN: 09317597
    Source: Wiley (via CrossRef)
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  • 9
    Language: English
    In: Angewandte Chemie International Edition, 14 January 2013, Vol.52(3), pp.854-857
    Description: : Diatoms use chemical signals to sense the presence of and find their mating partners. When the metabolic profiles of sexually active and inactive cells were compared, a highly up‐regulated metabolite generated in the attracting mating type was identified as di‐‐prolyl diketopiperazine, the first diatom pheromone.
    Keywords: Algae ; Cell Cycle ; Mass Spectrometry ; Metabolomics ; Pheromones
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 10
    Language: English
    In: Environmental Science and Policy, February 2018, Vol.80, pp.95-104
    Description: In 2014 temperate zone emission factor revisions were published in the IPCC Wetlands Supplement. Default values for direct CO emissions of artificially drained organic soils were increased by a factor of 1.6 for cropland sites and by factors ranging from 14 to 24 for grassland sites. This highlights the role of drained organic soils as emission hotspots and makes their rewetting more attractive as climate change mitigation measures. Drainage emissions of humic soils are lower on a per hectare basis and not covered by IPCC default values. However, drainage of great areas can turn them into nationally relevant emission sources. National policy making that recognizes the importance of preserving organic and humic soils’ carbon stock requires data that is not readily available. Taking Ireland as a case study, this article demonstrates how a dataset of policy relevant information can be generated. Total area of histic and humic soils drained for agriculture, resulting greenhouse gas emissions and climate change mitigation potential were assessed. For emissions from histic soils, calculations were based on IPCC emission factors, for humic soils, a modified version of the ECOSSE model was used. Results indicated 370,000 ha of histic and 426,000 ha of humic soils under drained agricultural land use in Ireland (8% and 9% of total farmed area). Calculated annual drainage emissions were 8.7 Tg CO e from histic and 1.8 Tg CO e from humic soils (equal to 56% of Ireland’s agricultural emissions in 2014, excluding emissions from land use). If half the area of drained histic soils was rewetted, annual saving would amount to 3.2 Tg CO e. If on half of the deep drained, nutrient rich grasslands drainage spacing was decreased to control the average water table at −25 cm or higher, annual savings would amount to 0.4 Tg CO e.
    Keywords: Lulucf ; Greenhouse Gas ; Histosol ; Peatland ; Organic Soil ; Iwms ; Environmental Sciences
    ISSN: 1462-9011
    E-ISSN: 1873-6416
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