Community composition of bacterial biofilms on two submerged macrophytes and an artificial substrate in a pre-alpine lake

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 Cytophaga-Flavobacter-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