New species of Nostoc (cyanobacteria) isolated from Pune, India, using morphological, ecological and molecular attributes

Filamentous cyanobacterium (strain NE-PS) isolated from a freshwater body in Pune, India, is being described as new species of the polyphyletic genus Nostoc. Phenotypic and molecular characterizations were performed, and the combined results validated the strain as a new species. Careful observations of the filaments, the presence of a distinct sheath throughout the length of the trichome, prominent differences in the shape and dimensions of the vegetative cells, heterocytes and the akinetes provided reliable morphological signals that the strain differed from rest of the closely related species. Sequencing of the 16S rRNA gene showed 98.66 % sequence similarity with Nostoc linckia, while rbcL and psbA sequencing showed 97 and 94 % similarities with Nostoc sp. PCC 7906 and Nostoc punctiforme PCC 73102, respectively, while the nifD gene sequence similarity was found to be 96 % with N. punctiforme Ind35 and Desmonostoc muscorum. The PC-IGS region was sequenced and concatenated cpcB, IGS and cpcA regions indicated the closest similarity with Nostoc linckia PACC 5085 at 96 %. Subsequent phylogenetic analyses gave a strong pattern of distinct clustering in case of all the molecular markers. The phenotypic, genetic and phylogenetic observations prove conclusively that the strain NE-PS is a new species in the genus Nostoc with the name proposed being Nostoc punensis, sp. nov.