Uncovering cyanobacterial diversity in Northeast India: phylogenetic and structural insights from heterocystous Strains

The North-East region of India, a recognised Indo-Myanmar biodiversity hotspot, remains underexplored for its cyanobacterial diversity. In this study, ten heterocystous cyanobacterial strains were isolated from freshwater-associated habitats using a polyphasic approach integrating morphological, molecular, and structural analyses. Morphological identification was complemented by 16S rRNA gene sequencing, phylogenetic reconstruction, and secondary structure prediction. The isolates were assigned to the genera Anabaena , Scytonema , Nostoc , Calothrix , Hapalosiphon , and Neowestiellopsis . Notably, one isolate corresponded to Neowestiellopsis sp. BTA1159 a taxon previously reported only from Iran marking the first record of this genus from Manipur and the second global report. Phylogenetic analysis using the neighbour-joining method (p-distance, Jukes Cantor correction) revealed that Neowestiellopsis sp. BTA1159 occupied a distinct polyphyletic position, while Calothrix sp. BTA1160 formed an outbranch. Minimum free energy (MFE) calculations for 16S rRNA secondary structures indicated that Neowestiellopsis sp. BTA1159 exhibited the highest structural stability among all isolates. These findings not only document novel cyanobacterial diversity from a globally significant hotspot but also demonstrate the utility of secondary structure analysis in complementing phylogenetic resolution.