A polyphasic approach for the taxonomy of cyanobacteria: principles and applications

Taxonomic classification is the only method for understanding and exploring knowledge about organismal diversity. However, it is complicated in prokaryotic, phylogenetically old, phototrophic cyanobacteria, which contain very simple unicellular forms up to multicellular types with a differentiated and diversified thallus. Their cells are cytologically relatively simple, but variable in shape. Various genotypes are adaptable to various specialized ecosystems. The introduction and combination of modern molecular, cytomorphological and ecological methods in the taxonomy of cyanobacteria is necessary and should be accepted as the only method for the elaboration of their modern systematics. The combination of different methods should be based on molecular sequencing as the basic approach, to which must be added other criteria (morphological, ecological) if they are available and which are distinct and recognizable in cyanobacterial populations. The use of such characteristics is necessary and must be obligatorily included for the final characterization both of strains and natural populations. Application of this polyphasic, i.e. combined approach is considered as a unique, modern, unambiguous, unequivocal and a fully acceptable methodological procedure, but it is not yet commonly used, nor possible for all known cyanobacterial populations. The main principles and recent problems of this modern classification method are discussed in the following review and will be the basis of further discussion.