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Community composition and interactions of biofilm bacteria on submerged freshwater macrophytes

Community composition and interactions of biofilm bacteria on submerged freshwater macrophytes


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HEMPEL, Melanie, 2008. Community composition and interactions of biofilm bacteria on submerged freshwater macrophytes

@phdthesis{Hempel2008Commu-7671, title={Community composition and interactions of biofilm bacteria on submerged freshwater macrophytes}, year={2008}, author={Hempel, Melanie}, address={Konstanz}, school={Universität Konstanz} }

deu Hempel, Melanie The aim of my PhD thesis was to investigate the bacterial biofilm community composition (BCC), on submerged macrophytes. The special interest was the composition and succession of the heterotrophic biofilm and possible influences such as environmental factors, habitat and plants on the biofilm and the interaction of isolates with each other and with aquatic herbivores. On the littoral zones of lakes, macrophytes offer a large area for colonization of bacteria and algae. Interactions between plant and epiphytes are frequent and can be positive and negative for both sides. Interactions between macrophytes and BCC can be mediated by structural changes of the surface or by exuded organic compounds. Especially secondary metabolites of plants (e.g., phenols) are known to have an impact on other phototrophs or microorganisms.factors<br />I expected that the phenol-rich milfoil Myriophyllum spicatum L. would have a different BCC than the pondweed Potamogeton perfoliatus, the stonewort Chara aspera or artificial substrates (polypropylene sheets). M. spicatum exudes algicidal and bactericidal polyphenols, while some Chara species produce algicidal cyclic sulphur compounds. It is not known if P. perfoliatus synthesizes polyphenols and if it may inhibit bacterial and algal growth. Another aspect of this work was to investigate the influence of leaf age on the BCC, since M. spicatum displays a distinct gradient of macronutrients and polyphenols from young apical meristems to older leaves. Both Chara aspera and M. spicatum occur in Lake Constance (freshwater) and in the Schaproder Bodden (brackish water). We compared the BCC on both macrophytes in both habitats. All analyses of the BCC in this study have been done with FISH and in Lake Constance additionally with DGGE and the construction of a clone library.<br />All investigations of the BCC lead to the conclusion that it was dominated by bacteria of the CFB-group, irrespective of substrate type. Alpha- and betaproteobacteria were the second most abundant groups, while planctomycetes were only found on brackish water C. aspera. Planctomycetes were largely influenced by the habitat and the substrate type (plant species) while bacteria of the CFB-group were rather influenced through plant species and leaf age.<br />The BCC comparison on M. spicatum, P. perfoliatus and the artificial substrates was not influenced by season. However, environmental factors such as water level and temperature, conductivity, pH and the carbon and total phenolic content of the plant tissue influenced the bacterial biofilm community composition. The BCC on the artificial substrates was more similar to that on P. perfoliatus than to that on M spicatum. The results obtained in all those community studies revealed a rather distinct and heterogeneous BCC on M. spicatum apices. Assumingly, this is a consequence of the high polyphenol content in these plant parts. The data obtained in the clone library support this finding. According to GenBank, most of the sequences obtained in the clone library do belong to bacteria not yet cultured.<br />We were able to isolate three bacterial strains from the biofilm (Pantoea agglomerans & Agrobacterium vitis) and the surrounding water (Matsuebacter sp.) of M. spicatum. All three are able to degrade polyphenols. With an especially designed experimental set-up, we tested if the three isolates were capable to colonize axenic M. spicatum.<br />Since epiphytes are taken up inevitably during feeding of herbivores they may have an impact on digestion and gut microbiota. In no choice feeding experiments I investigated, if the polyphenol degrading Matsuebacter sp. has an impact on the larval growth of the aquatic moth Acentria ephemerella (DENIS & SCHIFFERMÜLLER).<br />In comparison to axenic M. spicatum, plants colonized with Matsuebacter sp. had no negative or positive impact on larval growth. Thus we conclude that Matsuebacter sp. neither serves as an additional nutrient source, nor influences the gut microbiota or alters the exuded plant polyphenols.<br />While the influence of Matsuebacter sp. on larval growth was negligible, we could prove that this bacterium forms dense biofilms on M. spicatum rather quickly. The presence of Matsuebacter sp. reduces the biofilm formation of the agriculturally used bio control agent P. agglomerans, and that of the plant pathogen A. vitis is enhanced.<br />With this work, I contributed to the scarce knowledge on bacterial biofilms on aquatic plants. Further I elucidated the biofilm formation and interactions of single strains and their impact on higher trophic levels. Single bacterial groups are obviously influenced by the substrate and habitat type. Bacterial communities in their whole are rather determined by environmental factors like water level and temperature, and conductivity, and also the plant carbon and total phenolic content. Community composition and interactions of biofilm bacteria on submerged freshwater macrophytes deposit-license application/pdf Hempel, Melanie 2011-03-24T17:36:15Z 2008 2011-03-24T17:36:15Z

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

Dissertation_Hempel.pdf 129

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