Martin W. HahnAustrian Academy of Sciences, Institute for Limnology, Mondsee, Austria |
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Biogeography and Ecology of Bacteria: What are Appropriate Taxa for Investigations? |
| Diversity and biogeography of bacteria are research topics of increasing importance and interest. Despite recent advances in cultivation-independent methods (e.g., environmental genomics), research on these topics is still hampered by our current inability to cultivate representatives of many bacterial groups playing important ecological roles in natural ecosystems. For instance, only a minority of bacterial groups abundant in freshwater bacterioplankton is currently represented by cultivated strains. Due to the lack of appropriate cultivation methods, cultivation-independent methods are almost exclusively used in research on ecology and diversity of free-living bacteria. Frequently, this research is using ribosomal markers, i.e. 16S rRNA gene sequences, for the characterization and discrimination of taxa.
We investigated if such markers provide a sufficient phylogenetic resolution for revealing the biogeography and ecology of planktonic freshwater bacteria. We used bacteria affiliated with the subspecies Polynucleobacter necessarius subsp. asymbioticus as a model group. This taxon represents a ubiquitous and numerically important (up to 60% of total bacterioplankton) fraction of freshwater bacterioplankton. We cultured > 200 strains representing this taxon, and reconstructed the phylogeny of this taxon by using markers providing higher phylogenetic resolutions than the conserved 16S rRNA genes. We developed methods for detection of phylogenetic subgroups in environmental samples based on this phylogenetic framework. We investigated the distribution of a subgroup represented by a genome-sequenced strain in a set of > 100 freshwater habitats representing a broad limnological gradient. We confirmed the ubiquitous distribution of the investigated Polynucleobacter subspecies in the investigated freshwater habitats, but observed that the investigated subgroup was restricted to habitats representing a certain habitat type. On the other hand, this subgroup did not show a biogeography within the investigated area (100 km maximum distance between the investigated habitats). Additional ecophysiological experiments demonstrated complete niche separation between the investigated subgroup and other subgroups of the Polynucleobacter subspecies. All these findings would have been overlooked if the study had been performed on a higher taxonomic level, e.g. on the subspecies or species level. |
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Ort |
| 13.11.2008 15:00 Uhr
Großer Hörsaal |
© IGB |