Control of bacterial biofilm communities by protozoans under semi-natural conditions

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Biofilms, the complex communities of microbiota in association with solid substrates, play an important role in the matterflux of aquatic ecosystems. In the course of the present study it is planned to analyze for the first time the role of unicellular grazers (protozoans) in controlling the structure of biofilm-dwelling bacteria communities under semi-natural conditions. The biofilms will be established in micro-chambers ( flow cells ) and inoculated by either natural water from the River Rhine (the grazer composition will be manipulated by size fractionation here) or by field isolates of complex bacterial communities in combination with the controlled addition of specific grazers. These different approaches will be applied to test the effects of natural grazer communities with different complexities (containing either flagellates as first order-consumers alone, or additional ciliates as higher-order consumers), or the effects of specific grazer species. Different stages of the biofilm development will be considered. The morphological structure of the bacterial communities will be analyzed by confocal laser-scanning microscopy, its composition by a DNA-fingerprinting method (DGGE) in combination with sequencing of relevant bands. The expected results on the control of bacterial biofilms are relevant for different research areas including environmental and applied microbial ecology.