Molecular Evolution and Taxonomy of the Cyanobacteria

Molecular biology has provided new tools to decipher genetic information and can be used in attempts to reconstruct the evolution of organisms and improve their taxonomy. In the cyanobacteria, the use of molecular methods to study the genotypic relationships is underway, and initial results are promising. Different chemotaxonomic and macromolecular techniques are reviewed and their usefulness is evaluated. The most complete phylogenetic scheme of the cyanobacteria which is presently available is based on 16S rRNA sequence analysis. With this method, controversial taxonomic problems have been solved, such as the relationships among Pseudanabaena sp. strains or between the genera Arthrospira and Spirulina. In other cases, additional 16S rRNA sequences are necessary to obtain a clear picture. In addition to the cultivated strains, molecular ecology studies have contributed to the determination of new 16S rRNA sequence types, that have been retrieved directly from natural populations. The corresponding morphologies are presently unknown but may be revealed by the use of labeled probes annealing to specific 16S rRNA regions. For taxonomic purposes, it is necessary to find morphological features and simple testing methods which are congruent with the genotypic groupings. This information may be used to evaluate and revise existing classifications. The first stage in the development of such a polyphasic taxonomy is now underway.