IN-SITU IDENTIFICATION OF BACTERIA IN DRINKING-WATER AND ADJOINING BIOFILMS BY HYBRIDIZATION WITH 16S-RIBOSOMAL-RNA-DIRECTED AND 23S-RIBOSOMAL-RNA-DIRECTED FLUORESCENT OLIGONUCLEOTIDE PROBES

Free-water-phase and surface-associated microorganisms from drinking w ater were detected and roughly identified by hybridization with fluore scence-labeled oligonucleotide probes complementary to regions of 16S and 23S rRNA characteristic for the domains Bacteria, Archaea, and Euc arya and the beta and gamma subclasses of Proteobacteria. Samples of g lass-attached biofilms and plankton were taken from a Robbins device i nstalled in a water distribution system. More than 70% of the surface- associated cells and less than 40% of the planktonic cells visualized by 4',6-diamidino-2-phenylindole staining bound detectable amounts of rRNA-targeted probes. These findings are an indication for higher aver age rRNA content and consequently higher physiological activity of the attached microbial cells compared with the free-living cells. All det ectable cells hybridized with the bacterial probe, whereas no Archaea and no Eucarya cells could be detected. Simultaneous hybridization wit h probes specific for the beta and gamma subclasses of Proteobacteria revealed that microcolonies already consisted of mixed populations in early stages with fewer than 50 cells. These observations provide furt her evidence that the coexistence and interaction of bacteria in drink ing water biofilms may be an integral part of their growth and surviva l strategies.