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As a result of the continuous revision of cyanobacterial taxonomy, Phormidium autumnale (Agardh) Trevisan ex Gomont, 1892 has been transferred to the genus Microcoleus as Microcoleus autumnalis (Gomont, 1892) Strunecky, Koma'rek & J.R.Johansen, 2013. This transfer was based on a single strain and literature data. In the present study, we revise the taxonomic position of Microcoleus autumnalis by applying the classical approach of polyphasic taxonomy and additionally using metabolomics. Cyanobacterial strains identified as Phormidium autumnale and Microcoleus vaginatus (type species of the genus Microcoleus) were used for comparative analyses. In addition, the taxonomic relationship between the species Phormidium autumnale and Phormidium uncinatum was determined on the basis of polyphasic characteristics. Monitoring of the morphological variability of Phormidium autumnale and Microcoleus vaginatus strains showed a difference in the morphology concerning the ends of the trichomes, the shape of the apical cells, as well as the presence/absence of the calyptra and its shape. The performed TEM analysis of the thylakoid arrangement of the studied strains showed parietal arrangement of the thylakoids in the representatives of genus Phormidium and fascicular arrangement in genus Microcoleus. Molecular genetic analyses, based on 16S rDNA, revealed grouping of the investigated P. autumnale strains in a separate clade. This clade is far from the subtree, which is very clearly formed by the representatives of the type species of genus Microcoleus, namely M. vaginatus. The metabolomic analysis involving P. autumnale and M. vaginatus strains identified 39 compounds that could be used as potential biochemical markers to distinguish the two cyanobacterial species. Based on the data obtained, we suggest changing of the current status of Microcoleus autumnalis by restoring its previous appurtenance to the genus Phormidium under the name Phormidium autumnale (Agardh) Trevisan ex Gomont, 1892 and distinguishing this species from genus Microcoleus. [ABSTRACT FROM AUTHOR]

As a result of the continuous revision of cyanobacterial taxonomy, Phormidiumautumnale (Agardh) Trevisan ex Gomont, 1892 has been transferred to the genus Microcoleus as Microcoleusautumnalis (Gomont, 1892) Strunecky, Komárek & J.R.Johansen, 2013. This transfer was based on a single strain and literature data. In the present study, we revise the taxonomic position of Microcoleusautumnalis by applying the classical approach of polyphasic taxonomy and additionally using metabolomics. Cyanobacterial strains identified as Phormidiumautumnale and Microcoleusvaginatus (type species of the genus Microcoleus ) were used for comparative analyses. In addition, the taxonomic relationship between the species Phormidiumautumnale and Phormidiumuncinatum was determined on the basis of polyphasic characteristics. Monitoring of the morphological variability of Phormidiumautumnale and Microcoleusvaginatus strains showed a difference in the morphology concerning the ends of the trichomes, the shape of the apical cells, as well as the presence/absence of the calyptra and its shape. The performed TEM analysis of the thylakoid arrangement of the studied strains showed parietal arrangement of the thylakoids in the representatives of genus Phormidium and fascicular arrangement in genus Microcoleus . Molecular genetic analyses, based on 16S rDNA, revealed grouping of the investigated P.autumnale strains in a separate clade. This clade is far from the subtree, which is very clearly formed by the representatives of the type species of genus Microcoleus , namely M.vaginatus . The metabolomic analysis involving P.autumnale and M.vaginatus strains identified 39 compounds that could be used as potential biochemical markers to distinguish the two cyanobacterial species. Based on the data obtained, we suggest changing of the current status of Microcoleusautumnalis by restoring its previous appurtenance to the genus Phormidium under the name Phormidiumautumnale (Agardh) Trevisan ex Gomont, 1892 and distinguishing this species from genus Microcoleus ., Competing Interests: No conflict of interest to declare Disclaimer: This article is (co-)authored by any of the Editors-in-Chief, Managing Editors or their deputies in this journal., (Ivanka Teneva, Detelina Belkinova, Tsvetelina Paunova-Krasteva, Krum Bardarov, Dzhemal Moten, Rumen Mladenov, Balik Dzhambazov.)