Life on the rocks: polyphasic evaluation of three epilithic cyanobacterial strains isolated from a single rock, with the description of <i>Nostoc sikkimense</i> sp. nov., from the northeastern region of India

Three epilithic cyanobacterial strains were isolated from the scrapings of a single rock surface from the Reshi River in Sikkim, India. At the time of sampling, the rock surface did not show any visible cyanobacterial growth; however, the surface of the rock was glistering. Subsequent morphological analysis indicated that two out of three strains exhibited typical Nostoc-like morphology and the third strain had cell division in multiple planes showing typical morphology of a member of the family Hapalosiphonaceae. Further, 16S rRNA gene phylogeny indicated the strains to be members of the genera Nostoc, Desmonostoc, and Westiellopsis. For species-level demarcation, additionally, 16S-23S ITS (Internal Transcribed Spacer) region analysis was performed, which indicated that the strain RESHI-1B-PS was a novel cyanobacterial lineage of the genus Nostoc, while the strains RESHI-1A-PS and RESHI-1C-PS were representatives of Desmonostoc sp. and Westiellopsis prolifica, respectively. Thus, in the current investigation, we have described an undocumented species of the cyanobacteria, which we named Nostoc sikkimense in accordance with the guidelines outlined in the International Code of Nomenclature for algae, fungi, and plants (ICN). The study also enumerates and illustrates different life cycle stages of N. sikkimense RESHI-1B-PS along with further expanding the geographic distribution of W. prolifica and its substantial ecological adaptability.