BACTERIAL PHYLOGENY BASED ON 16S AND 23S RIBOSOMAL-RNA SEQUENCE-ANALYSIS

Molecular phylogeny increasingly supports the understanding of organis mal relationships and provides the basis for the classification of mic roorganisms according to their natural affiliations. Comparative seque nce analysis of ribosomal RNAs or the corresponding genes currently is the most widely used approach for the reconstruction of microbial phy logeny. The highly and less conserved primary and higher order structu re elements of rRNAs document the history of microbial evolution and a re informative for definite phylogenetic levels. An optimal alignment of the primary structures and a careful data selection are prerequisit es for reliable phylogenetic conclusions. rRNA based phylogenetic tree s can be reconstructed and the significance of their topologies evalua ted by applying distance, maximum parsimony and maximum likelihood met hods of phylogeny inference in comparison, and by fortuitous or direct ed resampling of the data set. Phylogenetic trees based on almost equi valent data sets of bacterial 23S and 16S rRNAs are in good agreement and their overall topologies are supported by alternative phylogenetic markers such as elongation factors and ATPase subunits. Besides their phylogenetic information content, the differently conserved primary s tructure regions of rRNAs provide target sites for specific hybridizat ion probes which have been proven to be powerful tools for the identif ication of microbes on the basis of their phylogenetic relationships.