Identification of cyanobacterial species with overlapping morphological features by 16S rRNA gene sequencing

Four strains of two species of Nostoc, N. commune (VB512188 and VB516200) and N. punctiforme (VB511286 and VB512190), isolated from the exterior of stone monuments and maintained in culture, showed very similar morphological features. Analysis of partial 16S rRNA gene sequences of these taxa with N. commune and N. punctiforme sequences from GenBank gave confusing results. Nostoc commune VB516200 and N. punctiforme VB511286 grouped together while the other two strains were placed in other clades. Phylogenetic analysis of an alignment including sequences of Nostoc and Desmonostoc species (N. commune, N. punctiforme and D. muscorum) from GenBank along with these four taxa, N. commune (VB512188 and VB516200) and N. punctiforme (VB511286) formed a distinct clade. However, the other strain of N. punctiforme (VB512190) clustered with sequences from Nostoc sp. from Spain and Australia and was quite distant from the other Indian samples. These results showed that identification of cyanobacterial species requires both morphological analysis in culture, and the use of molecular techniques.