Prey selectivity of bacterivorous protists in different size fractions of reservoir water amended with nutrients

Hydrobiological Institute of the Academy of Sciences of the Czech Republic, Na Sádkách 7, CZ-37005, Ceské Budejovice, Czech Republic.
Environmental Microbiology (Impact Factor: 6.24). 08/2006; 8(8):1330-9. DOI: 10.1111/j.1462-2920.2006.01026.x
Source: PubMed

ABSTRACT An experiment designed to examine food preferences of heterotrophic nanoflagellates (HNF) grazing on bacterioplankton was performed in the freshwater Rímov reservoir (Czech Republic). Water samples were size-fractionated to obtain < 5 microm filtrate containing bacteria and HNF. To manipulate resource availability, < 5 microm treatments were incubated in dialysis bags submerged in the barrels filled with the unfiltered reservoir water amended with either orthophosphate or glucose or combination of both. We employed rRNA-targeted probes to assess HNF prey preferences by analysing bacterial prey in HNF food vacuoles compared with available bacteria. Actinobacteria (the HGC69a probe) were avoided by HNF in all treatments. Cytophaga-Flavobacterium-Bacteroidetes bacteria (the CF319a probe) were positively selected mainly in treatments in which bacteria were heavily grazed, the < 5 microm treatments, but this trend was less pronounced towards the end of the study. The members of a small subcluster of Betaproteobacteria (the R-BT065 probe) were mostly positively selected. The nutrient amendments differentially affected bacterioplankton dynamics in almost all treatments, and together with the size fractionation, altered HNF overall bacterivory as well as prey selection. Analyses of bacterivores in unfiltered treatments allowed to detect the effect of different protists on shifts in HNF selectivity observed in < 5 microm compared with unfiltered treatments.

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    ABSTRACT: Understanding how resource partitioning works among taxa is crucial to explain coexistence and competition within a community. Here, we assessed resource partitioning among freshwater bacterial groups from two oligotrophic lakes using four types of organic substrates as compound models. Substrate uptake patterns were examined by microautoradiography (MAR) combined with catalyzed reporter deposition fluorescent in situ hybridization (CARD-FISH). Four large taxonomic groups were found in the lakes, but Actinobacteria (AcI lineage) and Betaproteobacteria (R-BT cluster) dominated the bacterial assemblage. Monomers containing nitrogen and/or phosphorus were preferred over the ones containing only carbon. All groups were able to incorporate amino acids, adenosine triphosphate (ATP), and glucose.However, acetate was only taken up by ~10-12% of Bacteria and its uptake was not detected in Cytophaga-Flavobacteria. Apart from acetate, the contribution of a particular bacterial group to the uptake of a substrate was proportional to its relative abundance. In both lakes, we detected substrate partitioning between AcI Actinobacteria, that was overrepresented in glucose and acetate utilization, and R-BT Betaproteobacteria that dominated amino acid uptake. Our results strongly point to physiological niche separation of those bacterial groups in alpine lakes.
    Environmental Microbiology Reports 10/2014; DOI:10.1111/1758-2229.12240 · 3.26 Impact Factor
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    Dataset: EMR14


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