Тaxonomy of Cyanobacteria: The Era of Change

Until mid-1970s, cyanobacteria have been interpreted as algae despite they differed from other members of this taxonomic group by the absence of cell nucleus (that is currently considered among the characters of prokaryotic organization). However, when bacteria were interpreted as prokaryotes, blue-green algae became reattributed as cyanobacteria, and bacteriologists began to study their cultured strains with microbiology methods. But since these objects did not obey the provisions of bacteriological code (ICNB), development of their taxonomy had certain problems, especially regarding nomenclature, that could not be solved until early-2010s. Current changes in taxonomy of cyanobacteria result from the general progress in taxonomy of prokaryotes due to explosive accumulation of 16S rRNA gene sequencing data, particularly for uncultured objects. Advances in description of new cyanobacteral taxa are as follows: (I) based on polyphasic approach, new taxa ranging from species to order were published; (II) “dark” cyanobacteria demonstrating several types of non-photosynthetic metabolism were described; I(II) strains producing red-shifted chlorophylls d and f were published. Advances in nomenclature of cyanobacteria are: (IV) taxa validly published according to botanical code (ICN) are also considered valid under prokaryotic code (ICNP); (V) the category of phylum was introduced into ICNP, and due to valid publication of the type genus Cyanobacterium, phylum name Cyanobacteriota became legitimate; (VI) names of uncultured Candidatus objects could get a standing in nomenclature based on SeqCode in which type material is represented by genomic DNA sequences. Advances in classification of cyanobacteria are: (VII) evolutionary tree of oxygenic phototrophs and related phylotypes was construed; (VIII) phylogenomic system of orders and families was elaborated; (IX) ecogenomic system combining genomie analysis with genome distribution data was offered. A subject for future research is restriction of taxonomic redundancy in cyanobacteria, and further attempts to establish their species concept.