I. Huber (1), W. Ludwig (1), R. Amann (1). M. Simon (2) and K.H. Schleifer (1)
(1) Department of Microbiology, Technical University Munich, D-80290 München (2) Institute of Limnology, University of Constance, D-78434 Konstanz
Limnetic macroscopic organic aggregates (lake snow) from Lake Constance were analysed for the bacterial community structure by screening different 16S rRNA gene libraries, in situ cell hybridization and isolation of bacteria. A large number of clones of the different gene libraries of natural and artificial lake snow aggregates were screened by membrane hybridization techniques with different group specific oligonucleotide probes. For more detailed phylogenetic information various 16S rDNA clone inserts were completely or partially sequenced. The sequence data analysis using the software package ARB, revealed a high diversity of sequences. The majority of retrieved sequences indicated members of the beta- and alpha-subclass of Proteobacteria. These results were consistent with those obtained by in situ cell hybridization of different lake snow samples with group specific oligonucleotide probes. Based on the comparative sequence analysis of the 16S rRNA data base (TU München), oligonucleotide probes specific for several clones or clone groups could be designed. The in situ cell hybridization with these probes specific for lake snow communities allowed the detection, localization and abundance of so far unknown microorganisms. In parallel several bacteria were isolated from lake snow flocs and screened with group specific and clone specific oligonucleotide probes. For the first time it was possible to isolate bacterial strains directly retrieved by the rRNA approach from an environmental sample.
