Protistan Grazing on Marine Bacterioplankton

Jürgens, Klaus; Massana, Ramón

doi:10.1002/9780470281840.ch11

Cited by 131 publications

(113 citation statements)

References 276 publications

(256 reference statements)

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“…After this initial bottom-up stimulation, a strong top-down control was manifested by the marked changes observed in the temporal dynamics of bacteria, HNF, ciliates and their bulk grazing rates. These results are in agreement with the role of protist bacterivory as a dominant bacterioplankton loss factor (Pedrós-Alió et al, 2000;Jürgens and Massana, 2008). Although FLB-based methods might not always be a perfect proxy for grazing pressure, particularly on motile cells (González et al, 1993), we found a strong direct correlation (N = 9, Pearson's r = 0.89, P = 0.0011) between HNF abundance and FLB disappearance rate (grazing rates) (Figures 1a vs b), suggesting that the major factor determining the disappearance of bacteria in the experiment was the direct ingestion and digestion by HNF.…”

Section: Discussionsupporting

confidence: 78%

“…Still, pronounced imbalances in growth versus loss rates over relatively more limited spatiotemporal scales can lead to pronounced dynamics in bacterial abundance. However, as both types of mechanisms can become important under different conditions (Thingstad, 2000), there is still not an accepted general theory of the regulation of bacterial stocks and production in marine systems (Jürgens and Massana, 2008). Differences in susceptibility to bacterivory among bacteria have been suggested as a key aspect that could influence the regulatory mechanisms of marine bacteria and the relation between bottom-up and top-down controls (Jürgens and Massana, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Marine bacterial community structure resilience to changes in protist predation under phytoplankton bloom conditions

et al. 2015

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To test whether protist grazing selectively affects the composition of aquatic bacterial communities, we combined high-throughput sequencing to determine bacterial community composition with analyses of grazing rates, protist and bacterial abundances and bacterial cell sizes and physiological states in a mesocosm experiment in which nutrients were added to stimulate a phytoplankton bloom. A large variability was observed in the abundances of bacteria (from 0.7 to 2.4 × 10 6 cells per ml), heterotrophic nanoflagellates (from 0.063 to 2.7 × 10 4 cells per ml) and ciliates (from 100 to 3000 cells per l) during the experiment (∼3-, 45-and 30-fold, respectively), as well as in bulk grazing rates (from 1 to 13 × 10 6 bacteria per ml per day) and bacterial production (from 3 to 379 μg per C l per day) (1 and 2 orders of magnitude, respectively). However, these strong changes in predation pressure did not induce comparable responses in bacterial community composition, indicating that bacterial community structure was resilient to changes in protist predation pressure. Overall, our results indicate that peaks in protist predation (at least those associated with phytoplankton blooms) do not necessarily trigger substantial changes in the composition of coastal marine bacterioplankton communities.

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Section: Discussionsupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Marine bacterial community structure resilience to changes in protist predation under phytoplankton bloom conditions

et al. 2015

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“…It controls bacterial abundances in a wide range of ecosystem conditions, channels organic carbon to higher trophic levels, and releases inorganic nutrients that often are limiting primary production (Pernthaler, 2005;Jü rgens and Massana, 2008). There are two main approaches to estimate community bacterivory rates: tracer techniques that follow the fate of an added bacterial surrogate and manipulation techniques that uncouple predator and prey populations (Strom, 2000).…”

Section: Introductionmentioning

confidence: 99%

Grazing rates and functional diversity of uncultured heterotrophic flagellates

et al. 2009

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Aquatic assemblages of heterotrophic protists are very diverse and formed primarily by organisms that remain uncultured. Thus, a critical issue is assigning a functional role to this unknown biota. Here we measured grazing rates of uncultured protists in natural assemblages (detected by fluorescent in situ hybridization (FISH)), and investigated their prey preference over several bacterial tracers in short-term ingestion experiments. These included fluorescently labeled bacteria (FLB) and two strains of the Roseobacter lineage and the family Flavobacteriaceae, of various cell sizes, which were offered alive and detected by catalyzed reporter deposition-FISH after the ingestion. We obtained grazing rates of the globally distributed and uncultured marine stramenopiles groups 4 and 1 (MAST-4 and MAST-1C) flagellates. Using FLB, the grazing rate of MAST-4 was somewhat lower than whole community rates, consistent with its small size. MAST-4 preferred live bacteria, and clearance rates with these tracers were up to 2 nl per predator per h. On the other hand, grazing rates of MAST-1C differed strongly depending on the tracer prey used, and these differences could not be explained by cell viability. Highest rates were obtained using FLB whereas the flavobacteria strain was hardly ingested. Possible explanations would be that the small flavobacteria cells were outside the effective size range of edible prey, or that MAST-1C selects against this particular strain. Our original dual FISH protocol applied to grazing experiments reveals important functional differences between distinct uncultured protists and offers the possibility to disentangle the complexity of microbial food webs.

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“…This strategy inexorably retrieves the same species complexes (that is, Cafeteria, Paraphysomonas, or Neobodo spp.) that are known to be rare in marine plankton (Jü rgens and Massana, 2008). Abundant taxa identified by molecular surveys still remain uncultured, for example the bacterivorous MAST clades (Massana et al, 2006a).…”

Section: Introductionmentioning

confidence: 99%

“…P. ubique was brought into culture by mimicking oligotrophic conditions and Nitrosopumilus marinus were cultured in media amended with ammonia once molecular data revealed they were ammonia oxidizers. Similar culturing efforts have seldom been applied to marine protists, even though culture bias is perceived as a major limitation to investigate further the functional role and ecological significance of photosynthetic protists (Vaulot et al, 2008), being even more severe for the heterotrophic ones (Jü rgens and Massana, 2008).…”

Section: Introductionmentioning

confidence: 99%

Taming the smallest predators of the oceans

Campo¹,

Not²,

Forn³

et al. 2012

The ISME Journal

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Protists (unicellular eukaryotes) arguably account for most eukaryotic diversity and are central players of the biosphere. Known protist diversity and biology is largely based on cultured strains. Yet, environmental molecular surveys have unveiled entirely novel lineages that, as their prokaryotic counterparts, are essentially uncultured. Culture bias is an important drawback for any microbe-related science and is particularly severe for heterotrophic protists, which depend on organic food sources for growth. Here, we show how ecologically significant bacterivorous protists have been brought into culture by mimicking in situ conditions. Single cells sorted by serial dilution or flow cytometry were inoculated into seawater amended with natural bacterial assemblage at nearly in situ abundances. Strains belonging to lineages only known so far from environmental sequencing were isolated. Among them, Minorisa minuta gen. nov. sp. nov. forms a novel branch within Rhizaria, holding a key evolutionary position, and with an average size of 1.4 μm represents one of the smallest bacterial grazers known to date. It has a worldwide planktonic distribution and can account for 5% of heterotrophic protists communities in coastal waters. Physiological features of this strain can partly explain its success in the environment. Culturing ecologically relevant but elusive protists provide invaluable material for ecophysiology, genomics, ecosystem modeling and evolutionary issues.

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Protistan Grazing on Marine Bacterioplankton

Cited by 131 publications

References 276 publications

Marine bacterial community structure resilience to changes in protist predation under phytoplankton bloom conditions

Marine bacterial community structure resilience to changes in protist predation under phytoplankton bloom conditions

Grazing rates and functional diversity of uncultured heterotrophic flagellates

Taming the smallest predators of the oceans

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