The vairone Leuciscus souffia is a cyprinid fish that inhabits river systems in and around the Alps. The complete mitochondrial DNA control region (

Background: Plants and their heterotrophic bacterial biofilm communities possibly strongly interact, especially in aquatic systems. We aimed to ascertain whether different macrophytes or their habitats determine bacterial community composition. We compared the composition of epiphytic bacteria on two common aquatic macrophytes, the macroalga Chara aspera Willd. and the angiosperm Myriophyllum spicatum L., in two habitats, freshwater (Lake Constance) and brackish water (Schaproder Bodden), using fluorescence in situ hybridization. The bacterial community composition was analysed based on habitat, plant species, and plant part.

We compared the heterotrophic community composition of bacterial biofilms on the submerged macrophytes Myriophyllum spicatum and Potamogeton perfoliatus and on an artificial surface in Lower Lake Constance (Germany) on spatial (plant age) and temporal scales using denaturing gradient gel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). M. spicatum contains polyphenolic allelochemicals that inhibit algae, cyanobacteria, and heterotrophic bacteria, and possibly influence the community composition, whereas P. perfoliatus does not. In 2005, the community composition of bacterial biofilms on apices and leaves of M. spicatum differed significantly. In 2006, the biofilm communities on the apices or leaves of M. spicatum and P. perfoliatus and the artificial surface did not differ significantly, although all except one apex sample of M. spicatum formed a distinct cluster based on DGGE banding patterns. On all surfaces, members of the CytophagaFlavobacter-Bacteroidetes (CFB) group (16 to 22%), Alphaproteobacteria (19%), and Betaproteobacteria (7 to 31%) were abundant; Actinobacteria and Planctomycetes occurred less frequently. Sequences of DNA fragments excised from DGGE gels were mainly affiliated with yet uncultured clones originating from various freshwater habitats. Several sequences were from bacteria capable of degrading phenolic and aromatic compounds. The chemical composition of the 2 plant species and of the different parts of M. spicatum differed up to an order of magnitude. Differences in the biofilm community composition mainly depended on environmental factors (water level, conductivity, temperature, pH) and the plant chemical composition, especially the carbon and total phenolic content. Our results suggest that the biofilm community on M. spicatum apices is related to specific bacterial functions in this microenvironment.

Hydrolysable polyphenols are present in Myriophyllum spicatum L. at high concentrations of up to 25% of dry matter and are also excreted. Bacteria associated with the submerged macrophyte M. spicatum isolated from the surrounding water column and epiphytic biofilm were tested for their ability to degrade polyphenols. Several bacterial isolates were capable of growing with tannic acid as the sole carbon and energy source, among them Matsuebacter sp. FB25, Agrobacterium vitis EB26 and Pseudomonas sp. FB22. Cell suspensions of Matsuebacter sp. precultured on succinate were capable of degrading gallic acid, while those of A. vitis were not, indicating the constitutive presence of gallate-degrading enzymes in the former. When cells were precultured on gallic or tannic acid, cell suspensions of both strains exhibited an enhanced degradation rate of gallic acid. M. spicatum-derived hydrolysable polyphenols, which are comparable in structure to tannic acid, resulted in the same enhanced degradation rate of gallic acid or tellimagrandin II, the major M. spicatum polyphenol, by cell suspensions of Matsuebacter sp. FB25. The presence of polyphenoldegrading bacteria in the vicinity of M. spicatum explains the observed fast disappearance of tellimagrandin II and other hydrolysable polyphenols after excretion and has implications for allelochemical interference with competitors, herbivores and potential pathogenic microorganisms. The presence of Matsuebacter sp. and other polyphenol-degrading strains in such environments suggests a sufficiently strong effect of M. spicatum exudates to bring about selection in favour of highly specialised bacteria.KEY WORDS: Hydrolysable polyphenol · Submerged macrophyte · Allelochemistry · Biofilm · Betaproteobacteria · Burkholderiales · Myriophyllum spicatum · TanninResale or republication not permitted without written consent of the publisher

-Using field experiments, we investigated the effects of fish carcasses (so called 'food falls') on benthic fauna. We simulated food falls using freshly killed fish during two different seasons (spring and summer) in the littoral zone of a large, pre-alpine meso-oligotrophic lake in central Europe (Lake Constance, Germany). This study provides evidence that input in the form of fish carcasses may play an important role in nutrient dynamics within this ecosystem. The benthic communities in the vicitinity and underneath the food fall were strongly influenced by the food fall. The results show that this supply of organic matter has a significant influence on the relationships within the communities, which are clearly dominated by bacteria, followed by copepod nauplii, cyclopoid copepods, chironomids, and ostracods. Total decomposition was obtained between days 80 and 68 of the experiments. The food fall had a positively but not significant effect on meiofaunal assemblages in these experiments. Furthermore, the results showed a negative relationship between bacteria and meiofauna abundance, indicating grazing by the meiobenthos on the bacterial community. These findings support other studies that found that the meiofauna exerted a grazing pressure on the microbial community, where this process was important in the decomposition of carcasses. Moreover, this study shows the potential importance of fish carcasses in Lake Constance, where food falls may generate high abundances and diversity of the benthic fauna and support high bacterial activities in this littoral ecosystem.