Homology modeling in combination of phylogenetic assortment, a new approach to resolve the phylogeny of selected heterocystous cyanobacteria based on phycocyanin encoding cpcBA-IGS locus

The present communication deals with phylogenetic assessment of phycocyanin coding genes, based on their 3-D structures which is still in its infancy. Homology modeling of cpcA and cpcB in conjunction with molecular phylogenetics for 12 strains belonging to the heterocystous cyanobacteria has been performed with an aim to resolve the ambiguities in their phylogenetic positions. 3D structure has been deduced using Discovery studio while CHIMERA, PEROMALS3D and SALIGN tools have been used for studying the structure based diversity of cpcA and cpcB genes respectively. MEME suite has been further used for motif analysis. Calothrix brevissima Ind9 was the most divergent strain. Nostoc and Anabaena were found to be intermixed at structural level also. The phylogeny suggested monophyletic origin of the heterocystous clade. Conserved Signature Indels provides novel means of identification and also supported monophyletic origin of heterocystous cyanobacteria. At the structure level the secondary elements are more conserved. Overall data obtained through the 3D structure based phylogeny affirmed close association and similar origin of the two subsections. This approach provides better resolution and must be used along with molecular phylogenetics for better identification of cyanobacteria.