LAUSR

ABSTRACT The cyanobacterial genus Arthrospira Stizenberger ex Gomont 1892 includes some of the most commercially significant microalgae, commonly known under the taxonomically incorrect brand name ‘Spirulina’. However, the infrageneric classification of the genus is still undefined. Herein, the classification of two Arthrospira strains (Nigrita M1 and Nigrita C1) from a commercial culture installation was studied and a polyphasic meta-analysis approach to a representative number (> 30) of strains was applied, in an attempt to determine the taxonomic relationships among the existing Arthrospira strains. The combined analysis of molecular (16S rRNA, 16S-23S rRNA ITS and cpcBA-IGS sequences) and phenotypic (13 morphological and morphometric characters) data of the studied Arthrospira strains divided them into three clusters/taxa. The main two taxa, namely Taxon I and Taxon II, include planktonic representatives, with irregular and regular helical structure of the filament, respectively. In contrast, Taxon III comprises the benthic representatives of the genus. Arthrospira strains Nigrita M1 and Nigrita C1 fall into Taxon I and II, respectively. The combined phenotypic and phylogenetic analysis suggests classification of Arthrospira strains into three taxa as subspecies of a single species within the genus Arthrospira.