Insights into the phylogenetic inconsistencies of the genus and description of epilithic sp. nov. (Cyanobacteria, Nostocales) from Jammu and Kashmir, India.

A dark-coloured thin film of cyanobacteria growing on the bottom of a submerged stone was isolated from Basantgarh village in Udhampur district, Jammu and Kashmir, India. The isolated strain (designated 19C-PS) was characterized using a polyphasic approach. The strain exhibited typical -like morphology with a characteristic feature of having heterocytes in series. The 16S rRNA gene phylogeny placed the strain at a well-supported and distinct node. Notably, the recently described genus, , on the addition of more 16S rRNA gene sequences, reflected a critical split, which proved to be stable and well supported in all phylogenetic analyses of the 16S rRNA gene. Interestingly, CENA67 (type species of the genus) clustered together with our strain 19C-PS in the 16S rRNA gene phylogenetic analysis while the rest of the members of the genus were placed at a separate and distant node. This clearly indicated that strain 19C-PS is a member of . However, the results of phylogenetic analysis of ITS sequences only, in strains purported to belong to did not agree with the 16S rRNA gene results and placed our strain 19C-PS in a sister clade to three strains that have not yet been speciated, UHCC 0702, NIES-4103 and SA22, with falling into a separate clade. Further, folded secondary structures of the D1-D1', V2, BoxB and V3 helices of strain 19C-PS were found to be significantly different from those of all the phylogenetically related taxa. The study revealed an interesting case where low taxon sampling and phylogenomic interpretations came across as points of attention in cyanobacterial taxonomy. Based on the morphological, phylogenetic, 16S-23S ITS secondary structure analyses, we describe our strain as sp. nov. in accordance with the International Code of Nomenclature for algae, fungi and plants. This work also illuminates the need for further research to resolve the taxonomic discrepancies among strains.