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Berlin Brandenburg

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  • 1
    In: Journal of Phycology, August 2009, Vol.45(4), pp.807-811
    Description: Algae of various taxonomic groups are capable of assimilating dissolved organic carbon (DOC) from their environments (mixotrophy). Recently, we reported that, with increasing biomass of mixotrophs, heterotrophic bacteria did not increase. We hypothesized that algal uptake of external DOC may outweigh their release of DOC by exudation (H1). Here, we addressed an alternative hypothesis that algae did not assimilate external DOC but constrained the release of DOC (H2). In chemostat experiments, we cultured the mixotrophic Negoro together with heterotrophic bacteria. As external substrates, we used glucose, which was potentially available for both bacteria and algae, or fructose, which was available only for bacteria. We increased the biomass of algae by the stepwise addition of phosphorus. Bacterial biomass did not increase in experiments using glucose or when fructose was offered, suggesting that mechanisms other than algal mixotrophy (H1) kept concentrations of bacteria low. Measured exudation rates (percent extracellular release, PER) of mixotrophic algae ( W. Krüger) were very low and ranged between 1.0% and 3.5% at low and moderately high phosphorus concentrations. In contrast, an obligately phototrophic alga ( H. Ettl) showed higher exudation rates, particularly under phosphorus limitation (70%). The results support H2. If mixotrophy is considered as a mechanism to recycle organic exudates from near the cell surface, this would explain why algae retained mixotrophic capabilities although they cannot compete with bacteria for external organic carbon.
    Keywords: Algae ; Bacteria ; Chemostat ; Competition ; Doc ; Exudation ; Mixotroph
    ISSN: 0022-3646
    E-ISSN: 1529-8817
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  • 2
    Language: English
    In: Hydrobiologia, 2010, Vol.649(1), pp.379-383
    Description: To investigate the consequences of increased temperature and enhanced input of dissolved organic matter (DOM) into lakes for heterotrophicic bacteria and for mixotrophic algae which use DOM in addition to photosynthesis, the hypotheses were tested whether (1) both bacteria and mixotrophic algae benefit from increased input of DOM, or (2) increased DOM input enhances bacterial biomass and thereby decreases algal biomass. Growth experiments in batch cultures, exudation measurements, and competition experiments in chemostats were performed at two temperature levels. Increased temperature stimulated the autotrophic growth rate of Chlorella protothecoides . Bacteria and Chlorella increased their heterotrophic growth rates at higher DOM concentration at lower temperature whereas enhanced DOM concentration hardly stimulated their growth at higher temperature. In chemostats, enhanced input of soil extract increased both bacterial and algal biomass at lower temperature whereas bacterial biomass increased only slightly and algal biomass decreased at higher temperature. Thus, the temperature determines the response of microorganisms to enhanced DOM concentration.
    Keywords: Bacteria ; Mixotrophic algae ; Temperature ; DOM ; Climate change ; Chemostat
    ISSN: 0018-8158
    E-ISSN: 1573-5117
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  • 3
    Language: English
    In: Microbial Ecology, 2010, Vol.60(3), pp.618-627
    Description: As extreme environmental conditions strongly affect bacterial community composition (BCC), we examined whether differences in pH—even at low pH—and in iron and sulfate concentrations lead to changes in BCC of acidic mining lakes. Thereby, we tested the following hypotheses: (1) diversity of the bacterial community in acidic lakes decreases with reducing pH, (2) BCC differs between epilimnion and hypolimnion, and (3) BCC in extremely acidic environments does not vary much over time. Therefore, we investigated the BCC of three acidic lakes with different pH values (2.3, 2.7, and 3.2) by denaturing gradient gel electrophoresis (DGGE) and subsequent sequencing of DGGE bands as well as catalyzed reporter deposition-FISH (CARD-FISH). BCC did not significantly vary among the studied lakes nor differ much between water layers. In contrast, BCC significantly changed over time, which is contradictory to our hypotheses. Bacterial communities were dominated by Alpha-, Beta-, and Gammaproteobacteria, whereas Actino- and Acidobacteria rarely occurred. Cell numbers of both free and attached bacteria were positively related to DOC concentration. Overall, low pH and extreme chemical conditions of the studied lakes led to similar assemblages of bacteria with pronounced temporal differences. This notion indicates that temporal changes in environmental conditions including food web structure also affect unique communities of bacteria thriving at low pH.
    Keywords: Limnology ; Aquatic Ecological Zones ; Ph ; Mining Industry ; Universities And Colleges ; Sulfates;
    ISSN: 0095-3628
    E-ISSN: 1432-184X
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  • 4
    Language: English
    In: Journal of phycology, 2008, Vol.44(3), pp.616-623
    Description: Dissolved organic carbon (DOC) constitutes the bulk of organic carbon in aquatic environments. The importance of DOC utilization by mixotrophic algae is unclear since heterotrophic bacteria are regarded as more efficient users. We tested the hypothesis that algae decrease the DOC concentration in the light to lower levels than in darkness resulting in competitive exclusion of heterotrophic bacteria according to the mechanistic competition theory. We investigated (a) the uptake kinetics of glucose as a model substrate by two cultured algae and mixed bacteria populations, (b) the competition for glucose between algae and bacteria in chemostats, (c) the effect of discontinuous glucose supply in chemostats, and (d) the minimum glucose concentrations achieved in cultures of algae and bacteria. Bacteria showed higher specific-glucose-uptake rates than algae. In chemostats, algae became extinct in the dark and coexisted in the light where they decreased bacteria to lower densities. Discontinuous glucose supply promoted the algae compared to continuous substrate addition. Several algae consumed glucose to lower concentrations in the dark than in the light and showed lower or equal residual glucose concentrations than bacteria. Residual concentrations were not related to allometric traits (cell volume) and photosynthetic potential (chl content). Overall, the hypothesis was not supported, and mechanisms of competition for DOC obviously differed from those for particulate prey. However, since some algae showed lower or equal residual glucose concentrations than bacteria, algal dark uptake of DOC may be important in deep layers of many waters. ; Includes references ; p. 616-623.
    Keywords: Bacteria ; Algae ; Mixotrophy ; Doc ; Competition
    ISSN: 0022-3646
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  • 5
    Language: English
    In: International biodeterioration & biodegradation, 2012, Vol.69, pp.17-22
    Description: To investigate biofilm growth on paints under field conditions, we developed a modified approach enabling subsequent Confocal Laser Scanning Microscopy (CLSM) for the three-dimensional analysis of undisturbed samples. Painted polycarbonate slides were glued on polycarbonate panels mounted on a test raft in a harbour, and one slide per paint and depth was used on each of the five sampling dates over three months. On seven out of ten paints, biomass dry weight and chlorophyll a of biofilms increased nearly linearly over time whereas biofilm development was inhibited on three paints. Quantitative CLSM results revealed that extracellular polymeric substances were the dominating component of the biofilms. Since top-view CLSM did not enable the complete observation of thick biofilms, cryosections were prepared to determine biofilm thickness. Results of biofilm thickness were comparable to those of biomass and chlorophyll. The vertical extension of CLSM top-view images was not related to biomass dry weight and to biofilm thickness from cryosections and was, therefore, no suitable measure for biofilm characterisation. In contrast, biofilm thickness measured from cryosections was positively related to biomass dry weight indicating the need of cryosections for thick biofilms. ; p. 17-22.
    Keywords: Biofilm ; Biomass ; Paints ; Confocal Laser Scanning Microscopy ; Chlorophyll
    ISSN: 0964-8305
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 6
    Language: English
    In: Microbial Ecology, 2015, Vol.69(2), pp.361-371
    Description: The fate of allochthonous dissolved organic carbon (DOC) in aquatic systems is primarily controlled by the turnover of heterotrophic bacteria. However, the roles that abiotic and biotic factors such as light and DOC release by aquatic primary producers play in the microbial decomposition of allochthonous DOC is not well understood. We therefore tested if light and autochthonous DOC additions would increase allochthonous DOC decomposition rates and change bacterial growth efficiencies and community composition (BCC). We established continuous growth cultures with different inocula of natural bacterial communities and alder leaf leachates (DOC leaf ) with and without light exposure before amendment. Furthermore, we incubated DOC leaf together with autochthonous DOC from lysed phytoplankton cultures (DOC phyto ). Our results revealed that pretreatments of DOC leaf with light resulted in a doubling of bacterial growth efficiency (BGE), whereas additions of DOC phyto or combined additions of DOC phyto and light had no effect on BGE. The change in BGE was not accompanied by shifts in the phylogenetic structure of the BCC, but BCC was influenced by the DOC source. Our results highlight that a doubling of BGE is not necessarily accompanied by a shift in BCC and that BCC is more strongly affected by resource properties.
    Keywords: Bacterial growth efficiency ; Continuous cultures ; Carbon decomposition ; Leaf litter ; Photolysis
    ISSN: 0095-3628
    E-ISSN: 1432-184X
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  • 7
    Language: English
    In: 2015
    Keywords: Confocal Laser Scanning Microscopy (Clsm) ; Forests ; Land Use Change ; Dissolved Organic Carbon ; Watersheds ; Doc ; Ecosystems ; Rivers ; Plankton ; Algae ; Humification ; Bacterial Production ; Extracellular Matrix ; Freshness Index ; Benthic Organisms ; Biofilm ; Biofilm ; Carbon ; Bacteria ; Mineralization ; Streams ; Freshness ; Humification Index ; Landscapes
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 8
    Language: English
    In: 2009
    Description: We investigated the response of the microbial components of the pelagic food web to re-oligotrophication of large, deep Lake Constance where total phosphorus concentrations during mixing decreased from a maximum of 2.81 μmol L-1 in 1979 via 1.87 μmol L-1 in 1987 to 0.26 μmol L-1 in 2007. Measurements of heterotrophic bacteria, autotrophic picoplankton (APP) and heterotrophic nanoflagellates (HNF) in 2006 and 2007 were compared to values from 1987 to 1997. We hypothesized that the biomass and seasonal variability of all groups will decrease under more oligotrophic conditions due to reduced resource availability, particularly for APP and HNF but less for the competitively stronger bacteria. Average bacterial biomass between spring and autumn was unrelated to phosphorus, whereas the ratio of bacterial biomass to chlorophyll a concentration increased with decreasing trophy due to declining chlorophyll concentrations. In contrast, a unimodal relationship was found between APP and phosphorus with low biomass at low and high phosphorus concentrations and maximum biomass in between. Average HNF biomass decreased strongly by a factor of 10 30 with decreasing trophy, and chlorophyll-specific HNF biomass was unimodally related to phosphorus. The relative seasonal biomass variability did not change for any group during re-oligotrophication. To conclude, HNF responded much more strongly and bacteria less so than chlorophyll concentrations to oligotrophication, whereas APP exhibited a more complex pattern.
    Keywords: Hnf ; Ologotrophication ; App ; Lake Constance ; 570 ; Bacteria ; Microbial Loop ; Plankton Succession
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 9
    Language: English
    In: 2009
    Description: We investigated the response of the microbial components of the pelagic food web to re-oligotrophication of large, deep Lake Constance where total phosphorus concentrations during mixing decreased from a maximum of 2.81 μmol L-1 in 1979 via 1.87 μmol L-1 in 1987 to 0.26 μmol L-1 in 2007. Measurements of heterotrophic bacteria, autotrophic picoplankton (APP) and heterotrophic nanoflagellates (HNF) in 2006 and 2007 were compared to values from 1987 to 1997. We hypothesized that the biomass and seasonal variability of all groups will decrease under more oligotrophic conditions due to reduced resource availability, particularly for APP and HNF but less for the competitively stronger bacteria. Average bacterial biomass between spring and autumn was unrelated to phosphorus, whereas the ratio of bacterial biomass to chlorophyll a concentration increased with decreasing trophy due to declining chlorophyll concentrations. In contrast, a unimodal relationship was found between APP and phosphorus with low biomass at low and high phosphorus concentrations and maximum biomass in between. Average HNF biomass decreased strongly by a factor of 10–30 with decreasing trophy, and chlorophyll-specific HNF biomass was unimodally related to phosphorus. The relative seasonal biomass variability did not change for any group during re-oligotrophication. To conclude, HNF responded much more strongly and bacteria less so than chlorophyll concentrations to oligotrophication, whereas APP exhibited a more complex pattern.
    Keywords: Hnf ; Ologotrophication ; App ; Life Sciences ; Lake Constance ; Bacteria ; Microbial Loop ; Plankton Succession
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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