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Berlin Brandenburg

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  • 11
    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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  • 12
    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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  • 13
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 28 October 2003, Vol.100(22), pp.12776-81
    Description: The majority of organisms can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such "mixotrophy" is a widespread phenomenon in aquatic habitats and is observed in many protozoan and metazoan organisms. The strategy requires investment in both photosynthetic and heterotrophic cellular apparatus, and the benefits must outweigh these costs. In accordance with mechanistic resource competition theory, laboratory experiments revealed that pigmented mixotrophs combined light, mineral nutrients, and prey as substitutable resources. Thereby, they reduced prey abundance below the critical food concentration of competing specialist grazers [Rothhaupt, K. O. (1996) Ecology 77, 716-724]. Here, we demonstrate the important consequences of this strategy for an aquatic community. In the illuminated surface strata of a lake, mixotrophs reduced prey abundance steeply. The data suggest that, as a consequence, grazers from higher trophic levels, consuming both the mixotrophs and their prey, could not persist. Thus, the mixotrophs escaped from competition with and losses to higher grazers. Furthermore, the mixotrophs structured prey abundance along the vertical light gradient, creating low densities near the surface and a pronounced maximum of their algal prey at depth. Such deep algal accumulations are typical features of nutrient-poor aquatic habitats, previously explained by resource availability. We hypothesize instead that the mixotrophic grazing strategy is responsible for deep algal accumulations in many aquatic environments.
    Keywords: Food Chain ; Chlamydomonas -- Physiology
    ISSN: 0027-8424
    E-ISSN: 10916490
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  • 14
    Language: English
    In: Hydrobiologia, 2001, Vol.442(1), pp.165-176
    Description: The filtration rate of Daphnia galeata was determined in in situ experiments in Bautzen Reservoir and in laboratory experiments, where daphnids were exposed to filtrates that previously contained either natural phytoplankton or cultured eukaryotic algae ( Scenedesmus obliquus or Asterionella formosa ), respectively. Individual filtration rate (FR) was measured using fluorescent beads, taking into account ingested beads in the gut only. Compared to heated control treatments (100 °C), dissolved compounds released by the nutritious cultured algae during the preconditioning phase or by the natural phytoplankton assemblages from Bautzen Reservoir strongly reduced the filtration rate of D. galeata (down to 60%). Heating deactivated these dissolved compounds. A significant correlation was found between primary production measured in situ and the reduction of FR in the filtrate of reservoir water, indicating that extra-cellular products released during photosynthesis triggered the reduction of the filtration rate. The ratio of ingested to collected beads was used to quantify the proportion of food, which was not only collected but passed the mouth of D. galeata . The ratio of ingestion to collection was compared between filtered and unfiltered reservoir water both media identical with respect to the concentration of dissolved compounds, whereas other factors (e.g. food concentration, temperature, filtration rate) were different. The changes in this ratio between filtered and unfiltered reservoir water suggest that D. galeata is capable of a chemosensory control of the ingestion behaviour by detecting external metabolites.
    Keywords: grazing experiments ; Daphnia ; filtration rate ; phytoplankton ; primary production
    ISSN: 0018-8158
    E-ISSN: 1573-5117
    Source: Springer Science & Business Media B.V.
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  • 15
    In: Journal of Plankton Research, 2012, Vol. 34(10), pp.922-927
    Description: Ingestion of the large pelagic ciliates Stentor araucanus and S. amethystinus by the cyclopoid copepod Mesocyclops araucanus was independent of light conditions and copepod sex, but rates were twice as high on S. araucanus as on S. amethystinus . Copepods consumed 44–183% of their biomass daily. Absorption efficiency was 5–40%, while 20–30% of the ingested food was found in the faeces. In field samples, 32–93% of Mesocyclops had ingested Stentor, indicating the importance of this food source.
    Keywords: Predation ; Cyclopoid Copepods ; Mixotrophic Ciliates ; 〈Kwd〉〈Italic〉Stentor〈/Italic〉〈/Kwd〉 ; North Patagonian Lakes
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 16
    Language: English
    In: Journal of Microbiological Methods, February 2016, Vol.121, pp.8-10
    Description: A method for recovering CO respired by bacterioplankton for analysis of carbon isotopes was adapted for use with standard laboratory equipment without a technically demanding harvest line. The recovered CO was more depleted in C than the dissolved organic carbon (DOC) source, which suggests a selective respiration of older carbon.
    Keywords: Dissolved Organic Carbon (Doc) ; Inorganic Carbon (Ic) ; Degradation ; Carbon Isotopes ; Reservoir ; Biology
    ISSN: 0167-7012
    E-ISSN: 1872-8359
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  • 17
    In: Journal of Plankton Research, 2012, Vol. 34(2), pp.102-112
    Description: Aquatic bacteria are considered to exhibit a paradoxical behaviour. They luxuriously consume phosphorus, the element often restricting the abundance of algae, which provide the organic substrates maintaining bacterial growth. Here, we test the hypothesis that bacteria can limit their uptake of phosphorus and increase the availability of phosphorus to algae. The physiological costs for bacteria must be compensated for by a surplus of photosynthetic exudates facilitating higher biomass production. To test the potential of such an economic behaviour, we used a new differential equation model that was parameterized by independent experiments. Model results indicate that this potential does exist. As a consequence, we conducted continuous growth chemostat experiments. Bacteria did not leave more phosphorus to, “high exudation” algae compared with algae with low release. Therefore, the hypothesis was not supported by the experiments. However, bacteria significantly increased production 1.4–1.8-fold in cultures with “high exudation” algae. This was explained by an increase in conversion of organic carbon from growth medium into bacteria biomass. Algal exudates were quantitatively negligible but could act as growth factors. The results show that biomass of algae and bacteria cannot be predicted solely by mineral nutrients and carbon as assumed by the classical theory.
    Keywords: Bacteria ; Phytoplankton ; Exudation ; Phosphorus ; Differential Equation Model
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 18
    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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  • 19
    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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  • 20
    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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