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Digitale Medien

Confusing Selective Feeding with Differential Digestion in Bacterivorous Nanoflagellates (2001)

BOENIGK, JENS ; MATZ, CARSTEN ; JÜRGENS, KLAUS ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

The @journal of eukaryotic microbiology 48 (2001), S. 0

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ISSN: 1550-7408

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: Food selectivity and the mechanisms of food selection were analyzed by video microscopy for three species (Spumella, Ochromonas, Cafeteria) of interception-feeding heterotrophic nanoflagellates. The fate of individual prey particles, either live bacteria and/or inert particles, was recorded during the different stages of the particle-flagellate-interaction, which included capture, ingestion, digestion, and egestion. The experiments revealed species-specific differences and new insights into the underlying mechanisms of particle selection by bacterivorous flagellates. When beads and bacteria were offered simultaneously, both particles were ingested unselectively at similar rates. However, the chrysomonads Spumella and Ochromonas egested the inert beads after a vacuole passage time of only 2–3 min, which resulted in an increasing proportion of bacteria in the food vacuoles. Vacuole passage time for starved flagellates was significantly longer compared to that of exponential-phase flagellates for Spumella and Ochromonas. The bicosoecid Cafeteria stored all ingested particles, beads as well as bacteria, in food vacuoles for more then 30 min. Therefore “selective digestion” is one main mechanism responsible for differential processing of prey particles. This selection mechanism may explain some discrepancies of former experiments using inert particles as bacterial surrogates for measuring bacterivory.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1550-7408.2001.tb00175.x

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Digitale Medien

Seasonal dynamics of crustacean zooplankton, heterotrophic nanoflagellates and bacteria in a shallow, eutrophic lake (1995)

JÜRGENS, KLAUS ; STOLPE, GISELA

Oxford, UK : Blackwell Publishing Ltd

Freshwater biology 33 (1995), S. 0

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ISSN: 1365-2427

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: 1. The seasonal development of crustacean zooplankton, heterotrophic nanoflagellates (HNF) and bacteria was examined in Grosser Binnensee, a shallow, eutrophic lake in northern Germany. The grazing impact of Daphnia on bacteria and nanoflagellates was estimated from field data on population abundances and from clearance rates obtained in laboratory experiments.2. The seasonal succession of zooplankton showed distinct peaks of Daphnia magna, cyclopopid copepods, Bosmina longirostris and Daphnia galeata and D. hynlina. The population dynamics of Dapfinia had the strongest impact on all sestonic components. Daphnia maxima coincided with clearwater phases, and were negatively correlated with particulate organic carbon (POC), HNF and phytoplankton. Bacterial abundance was only slightly affected although daphnids were at times more important as bacterial consumers than HNF, as estimated from measured bacterial clearance rates. Other crustaceans (copepods, Bosmina) were probably of minor importance as grazers of bacteria and nanoplankton.3. HNF abundance varied from 550 ml−1 to more than 30000 ml−1. HNF appeared to be suppressed by daphnids and reached highest densities when copepods dominated the metazooplankton. The variation in HNF abundance was not reflected in the concentration of heterotrophic bacteria, which fluctuated rather irregularly between 5 and 20 ± 106 ml−1. Long filamentous bacteria which were probably resistant to protozoan grazing, however, appeared parallel to the development of HNF. These bacterial cells, although small in number, could comprise more than 30% of the total bacterial biomass.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-2427.1995.tb00383.x

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Digitale Medien

Phenotypic variation in Pseudomonas sp. CM10 determines microcolony formation and survival under protozoan grazing (2002)

Matz, Carsten ; Deines, Peter ; Jürgens, Klaus

Oxford, UK : Blackwell Publishing Ltd

FEMS microbiology ecology 39 (2002), S. 0

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ISSN: 1574-6941

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: We investigated the survival mechanism of the bacterium Pseudomonas sp. CM10 in the presence of a flagellate predator. The bacterium had been isolated from a continuous culture containing bacterivorous nanoflagellates. On agar plates, we found intraclonal dimorphism of Pseudomonas sp. CM10 colonies at high frequencies: The primary mucoid colony type generated a secondary non-mucoid form. Unlike the repeated generation of non-mucoid colonies from mucoid clones, we did not observe the occurrence of mucoid forms in non-mucoid populations. In semicontinuous and batch cultures, we investigated the ability of the two morphs to survive predation by the bacterivorous flagellate Ochromonas sp. under conditions of growth and starvation. In predator-free cultures, populations of both variants were unicellular but differed in some phenotypic characteristics such as cell motility and hydrophobicity. Grazing treatments revealed that the non-mucoid morph was reduced severely whereas the primary mucoid type survived due to the formation of inert suspended microcolonies stabilized by an extracellular matrix. Effectiveness and competitive trade-offs of microcolony formation were revealed by a competition experiment with the bacterium Pseudomonas putida MM1: Pseudomonas sp. CM10 was displaced in predator-free cultures but outgrew the defenseless and monomorphic competitor under flagellate grazing pressure. We conclude that intraclonal polymorphism may regulate the ability of Pseudomonas sp. CM10 to survive in situations of severe protistan grazing. The formation of inert microcolonies, however, is suggested to be detrimental to rapid growth and dispersal.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1574-6941.2002.tb00906.x

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Digitale Medien

Rapid Daphnia-mediated changes in microbial community structure: an experimental study (2002)

Degans, Hanne ; Zöllner, Eckart ; Gucht, Katleen ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

FEMS microbiology ecology 42 (2002), S. 0

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ISSN: 1574-6941

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: Shifts in morphological and taxonomical composition of bacterioplankton communities in response to protist and metazoan grazing were studied in bottle experiments, exposing bacterioplankton from a eutrophic clear-water pond, dominated by a large population of Daphnia magna, to a Daphnia gradient, ranging from 0 to 60 individuals per liter. Prior to the first experiment, the bacterioplankton community was shaped by protist grazing, while for the second experiment, bacterioplankton was pre-adapted to Daphnia grazing. In both experiments, rapid shifts in biomass and structure of the bacterioplankton community upon exposure to Daphnia grazing were observed. High Daphnia densities suppressed protozoa, resulting in a dominance of free-living bacteria. Under low Daphnia densities, heterotrophic nanoflagellates (HNF) developed as the dominant grazers and complex morphotypes (filaments, aggregates) were abundant in the bacterial community. Denaturing gradient gel electrophoresis analysis showed that taxonomical changes accompanied the morphological differences between bacterial communities shaped by HNF or Daphnia grazing. However, comparing ciliate- and Daphnia-dominated bacterial communities, we observed a discrepancy between morphological and taxonomical shifts, indicating that other traits than mere morphological ones determine vulnerability of bacterioplankton to specific grazers. Our results illustrate the rapid, pronounced and reversible impact of grazing on the morphology and taxon composition of bacterioplankton. Our results also stress that Daphnia may, already at moderate densities, have a pronounced impact on the lake bacterioplankton, both through direct grazing on the bacteria and through grazing on protozoan bacterivores.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1574-6941.2002.tb01003.x

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