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Aquatic Microbial Ecology

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AME 52:283-296 (2008)  -  DOI:

Effects of protozoan grazing within river biofilms under semi-natural conditions

Jennifer K. Wey, Anja Scherwass, Helge Norf, Hartmut Arndt, Markus Weitere*

Department of General Ecology and Limnology, Zoological Institute, University of Cologne, Weyertal 119,
50931 Cologne, Germany
*Corresponding author. Email:

ABSTRACT: Biofilms play an important role in the material flux of many aquatic ecosystems, but little is known about the mechanisms controlling their community structure under natural conditions. In the present study, we focused on the effects of ciliates on the quantity and taxonomic composition of heterotrophic flagellates (HF), and the effects of HF on the quantity and life forms (single cells vs. microcolonies) of bacteria in the early phase of biofilm colonization. For this purpose, we established semi-natural biofilms in flow cells connected to the river Rhine at Cologne, Germany. Using filter cartridges, we size-fractionated the potamoplankton, which is the source of the biofilm community, thus establishing biofilms containing (1) only bacteria (1.2 µm filter), (2) HF and bacteria (8 or 5 µm filter), or (3) ciliates, HF and bacteria (20 µm filter). The presence of ciliates negatively influenced the abundance of biofilm-dwelling HF and selectively altered the taxonomic composition of the HF community. The presence of HF resulted in a significant reduction in the abundance of single bacterial cells, but enhanced the abundance of bacterial microcolonies. Furthermore, the presence of ciliates stimulated the abundance of single-cell bacteria (probably due to an HF-mediated trophic cascade), but had no effect on bacterial microcolonies. Taken together, the results of this study show the importance of protozoan grazing in shaping the species composition and morphology of early river biofilms under semi-natural conditions.

KEY WORDS: River biofilm · Benthic protozoans · Size fractionation · Trophic cascade · Top-down control · Microbial communities

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Cite this article as: Wey JK, Scherwass A, Norf H, Arndt H, Weitere M (2008) Effects of protozoan grazing within river biofilms under semi-natural conditions. Aquat Microb Ecol 52:283-296.

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