| Summary: | 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 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. 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 ...
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