Taxonomic interpretation of non-heterocystous Cyanobacteria (Oscillatoriales) from eastern India with particular emphasis on Lyngbya Plectonema complex

Filamentous non-heterocystous cyanobacterial taxa from 8 genera were collected from different ecological niches like high altitudes, plains and estuaries of eastern India. The systematic accounts of 23 taxa were investigated with a polyphasic approach considering morpho taxonomy, cultural behavior, and molecular phylogenetic analysis with 16S and 16S-23S Internal Transcribed Spacer (ITS) regions as molecular markers. The collected taxa were from the families Oscillatoriaceae, Phormidiaceae and Pseudanabaenaceae with 8 representative genera viz. Lyngbya, Plectonema, Oscillatoria, Limnothrix, Leptolyngbya, Planktothrix, Desertifilum and Phormidium. The 16S-23S ITS region-based molecular characterization of 13 species from Oscillatoriaceae, 6 species from Phormidiaceae, and 4 species from Pseudanabaenaceae were found to be congruent with earlier phylogenetic studies using other markers. Phylogenetic tree analysis revealed habitat-specific clustering of ITS sequences of the investigated taxa. The 16S molecular marker-based phylogenetic analysis, along with cultural studies of the Lyngbya-Plectonema clade, highlighted the need for morphotaxonomic reconsideration of Lyngbya birgei and Plectonema tomasinianum related to the formation of false branching. The present study affirmed that 98% sequence similarity in the ITS region can be considered as a threshold percentage for conspecificity determination in the Lyngbya genus. Keywords: Cyanobacteria; ITS; Oscillatoriaceae; Phormidiaceae; Phylogenetic tree; Pseudanabaenaceae.