Nostoc thermotolerans sp nov., a soil-dwelling species of Nostoc (Cyanobacteria)

A filamentous, soil-dwelling cyanobacterial strain (9C-PST) was isolated from Mandsaur, Madhya Pradesh, India, and is described as a new species of the genus Nostoc. Extensive morphological and molecular characterization along with a thorough assessment of ecology was performed. The style of filament orientation, type and nature of the sheath (e.g. distribution and visibility across the trichome), and vegetative and heterocyte cell dimensions and shape were assessed for over one year using both the laboratory grown culture and the naturally occurring samples. Sequencing of the 16S rRNA gene showed 94% similarity with Nostoc piscinale CENA21 while analyses of the secondary structures of the 16S23S ITS region showed unique folding patterns that differentiated this strain from other species of Nostoc. The level of rbcl and rpoC1 gene sequence similarity was 91 and 94% to Nostoc sp. PCC 7524 and Nostoc piscinale CENA21, respectively, while the nifD gene sequence similarity was found to be 99% with Nostoc piscinale CENA21. The phenotypic, ecological, genetic and phylogenetic observations indicate that the strain 9C-PST represents a novel species of the genus Nostoc with the name proposed being Nostoc thermotolerans sp. nov. according to the International Code of Nomenclature for Algae, Fungi, and Plants.