Characterization of the microbial community of lotic organic aggregates ('river snow') in the Elbe River of Germany by cultivation and molecular methods

Aerobic and anaerobic cultivation techniques, 16S rDNA-based phylogeny, and fluorescent in situ hybridization were used to describe the phylogenetic d iversity and physiological versatility of lotic microbial aggregates ('rive r snow') obtained from the river Elbe. In the course of the year the 'river snow' community changed. It was characterized by a great bacterial diversi ty in spring, the predominant occurrence of algae in summer and reduction o f the total bacterial cell count in autumn and winter. In all 'river snow' samples, more than 70% of the bacteria counted with the general DNA stain D API also hybridized with the Bacteria-specific probe EUB338. In situ analys is of the bacterial 'river snow community with a comprehensive suite of spe cific rRNA-targeted probes revealed population dynamics to be governed by s easonal factors. During all seasons, beta-Proteobacteria constituted the nu merically most important bacterial group forming up to 54% of the total cel l counts. In contrast to this, the relative abundance of other major bacter ial lineages ranged from 2% for the order Planctomycetales to 36% for Cytop haga-Flavobacteria. Cultivation of 'river snow' under aerobic and anaerobic conditions with a variety of different media resulted in the isolation of 40 new bacterial strains. Phenotypic and phylogenetic analyses revealed the se new strains to be mostly unknown organisms affiliated to different bacte rial phyla. Application of newly developed specific oligonucleotide probes proved the cultivated bacteria. including clostridia and the numerically ab undant beta-Proteobacteria, as relevant in situ members of the;river snow' community. (C) 2000 Federation of European Microbiological Societies. Publi shed by Elsevier Science B.V. All rights reserved.