Multitude and temporal variability of ecological niches as indicated by the diversity of cultivated bacterioplankton

The diversity of cultured planktonic bacteria was analyzed. Bacterial strai ns were isolated from a eutrophic lake (Zwischenahner Meer, Niedersachsen, Germany) at three different sampling dates (October 1997, April and May 199 8). Phylogenetic diversity was assessed by polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE). and sequencing of 16S rRNA gene fragments. Enterobacterial repetitive intergenic consensus (ERIC:)-PC R revealed a high genomic diversity within the strain collections, which ex ceeded the diversity of the 16S rRNA gene sequences considerably. The compo sition of each of the three strain collections was unique since strains iso lated at different dates always exhibited different ERIC-PCR fingerprints. Growth tests with 59 different carbon substrates demonstrated that even str ains with identical ERIC-PCR fingerprints. isolated on one sampling date. d iffered in their physiology. The culturable fraction investigated in the pr esent study constituted a relatively small fraction (less than or equal to 15%) of the whole bacterioplankton assemblage. Nevertheless, the high physi ological diversity in this Fraction already indicates that a multitude of d ifferent ecological niches must exist in the planktonic environment. The ma jority of strains isolated in April prior to the decay of the phytoplankton bloom were members of the Cytophaga-Flavobacterium group. One month later, nor a single strain of this group could be isolated. When a group-specific PCR-DGGE technique was employed, rapid shifts in the diversity of non-cult ured Cytophaga-Flavobacteria also became evident. Based on the rapid shifts in the composition of cultivated as well as some non-cultivated bacteria, the ecological niches in the planktonic habitat must undergo rapid temporal changes. (C) 2001 Federation of European Microbiological Societies. Publis hed by Elsevier Science B.V. All rights reserved.