Taxonomy of cyanobacteria: the era of change

Abstract

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 a character of prokaryotic organization). However, when bacteria were reinterpreted 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), the 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 a general progress in taxonomy of prokaryotes due to the explosive accumulation of 16S rRNA gene sequencing data, particularly of uncultured objects. Advances in the description of cyanobactera are as follows: I) based on polyphasic approach, new taxa ranging from species to order were published; II) “dark” objects demonstrating several types of non-photosynthetic metabolism were described; III) the objects producing red-shifted chlorophylls d and f were published. Advances in the nomenclature of cyanobacteria are: IV) taxa validly published according to the botanical code (ICN) are also considered valid under the prokaryotic code (ICNP); V) category of phylum was introduced into ICNP, and due to valid publication of the type genus Cyanobacterium, the phylum name Cyanobacteriota became legitimate; VI) names of uncultured Candidatus objects could get standing in nomenclature based on the SeqCode in which type material is represented by genomic DNA sequences. Advances in the 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 genome analysis and genome distribution data was offered. The subject for future research is a restriction of taxonomic redundancy in cyanobacteria, and further attempts to develop their species concept.