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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
    In: Limnology and Oceanography, May 2000, Vol.45(3), pp.741-743
    Description: In experiments with axenic cultures of , we tested whether this cyanobacterium incorporates leucine, a compound that is often used for the measurement of heterotrophic bacterioplankton production. showed significant leucine incorporation, and the uptake of exponentially growing cells was higher than the uptake of cells in stationary growth phase. Therefore, the leucine method may not be suitable for measuring bacterial production in highly eutrophic waters with a dominance of cyanobacteria.
    Keywords: Oceanography;
    ISSN: 0024-3590
    E-ISSN: 1939-5590
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  • 3
    In: Freshwater Biology, August 2004, Vol.49(8), pp.1062-1071
    Description: 1. Lakes formed in mining pits often contain high concentrations of dissolved ferric iron and sulphate (e.g. 2 and 16 mmol L, respectively) and the pH is buffered between 2.5 and 3.5. Efforts to neutralise their water are based on the stimulation of lake internal, bacterial iron‐ and sulphate reduction. Electron donors may be supplied by organic carbon compounds or indirectly by enhancement of primary production. Here, we investigated the function of mixotrophic algae, which can potentially supplement or deplete the organic carbon pool, in the carbon metabolism and alkalinity budget of an acidic mining lake. 2. Two weeks after organic substrates had been added in a large mesocosm of 30 m diameter, a bloom of occurred, reaching a biovolume of 80 mm L. Growth experiments using filtered lake water showed that the alga reduced the overall dissolved organic carbon (DOC) concentration despite significant photosynthetic activity. However, when were grown together with natural bacterioplankton, net DOC consumption did not increase. 3. Uptake experiments using [C]‐glucose indicated that bacteria dominated glucose uptake and remineralisation. Therefore, the DOC leached in the water column was processed mainly by planktonic bacteria. Leached DOC must be regarded as loss, not transferred by larger organisms to the sediment, where reduction processes take place. 4. From phytoplankton biomass and production 2 years after fertilisation we estimated that pelagic photosynthesis does not supply an electron donor capacity capable of reducing more than 2% of actual stock of acidity per year. We estimated that only the benthic primary production was in a range to compensate for ongoing inputs of iron and sulphate.
    Keywords: Acidic ; Chlamydomonas ; Mining Lakes ; Mixotrophic ; Organic Carbon
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 4
    In: Freshwater Biology, May 2001, Vol.46(5), pp.633-639
    Description: 1. After observing that juvenile roach fed intensively on cyanobacteria and that cyanobacteria were densely colonized by heterotrophic bacteria, we tested whether the bacteria are used by underyearling roach and the extent to which they contribute to the energy requirements of the fish. 2. We radiolabelled attached bacteria in a natural cyanobacterial suspension, fed the fish with these particles, and estimated their assimilation by roach. Biomass of attached bacteria on cyanobacteria increased with the proportion of the cyanobacterium in total cyanobacteria. Biomass‐specific thymidine incorporation of attached bacteria was higher than that of free bacteria. 3. In feeding experiments, we detected assimilation of bacterial biomass into muscle tissue of underyearling roach. Fish consumed to a lesser extent compared with but assimilation of attached bacteria was higher when roach fed on because of the higher biomass of epibacteria on this cyanobacterium. However, biomass of attached bacteria was too low to be an important food source for underyearling roach. 4. We conclude that assimilation of epibacteria from cyanobacteria cannot explain the success of roach in eutrophic lakes.
    Keywords: Attached Bacteria ; Bacterial Production ; Cyanobacteria ; Microcystis ; Roach
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 5
    In: Limnology and Oceanography, November 2003, Vol.48(6), pp.2392-2396
    Description: Herbivorous fish feed on cyanobacteria. Digestability differs, however, between cyanobacteria species without mucous cover and mucilaginous genera such as . The latter can pass fish guts almost undamaged, and it has been hypothesized that they can take up nutrients during gut passage. Here we tested whether live , as food for juvenile roach labeled with P, indeed showed higher radioactivity after gut passage as compared to gut contents in control experiments with fish fed heated . showed high viability after passage through roach guts, and live colonies had a significantly higher radioactivity than dead ones. We conclude that is protected against digestion in roach guts and can directly use the phosphorus supplied in the fish guts during passage.
    Keywords: Oceanography;
    ISSN: 0024-3590
    E-ISSN: 1939-5590
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  • 6
    In: Freshwater Biology, 09 February 2002, Vol.47(2), pp.243-250
    Description: 1. The ability of roach to use cyanobacterial food is generally believed to be one reason for the dominance of roach over perch in eutrophic European lakes. The aim of this study was to test whether cyanobacteria really are a suitable food for juvenile roach. Special attention was paid to differences between the two cyanobacteria species and which are common in eutrophic lakes and are ingested by roach there. 2. We performed growth and behaviour experiments with juvenile roach fed with zooplankton and the different cyanobacteria. Growth rate with was lower than with but significantly higher than without food, whereas growth rate with was as low as without food. 3. In cultivation experiments of roach faeces, was found not to have been digested and grew exponentially after passing through the gut whereas stayed at low biomass. Differences in growth were not related to the toxin content of cyanobacteria. Investigations of roach motility showed no differences whether fed with or . 4. In contrast to , can be regarded as a suitable food source for juvenile roach probably because of its better digestability. We conclude that the ability to feed on cyanobacteria is not a general competitive advantage for roach, but the outcome depends on the species composition of the cyanobacteria.
    Keywords: Aphanizomenon ; Cyanobacteria ; Microcystis ; Roach ; Zooplankton
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 7
    In: Journal of Phycology, June 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.
    Keywords: Algae ; Bacteria ; Competition ; Doc ; Mixotrophy
    ISSN: 0022-3646
    E-ISSN: 1529-8817
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