Studies of cyanobacterial species are important to the global scientific community, mainly, the order, Nostocales fixes atmospheric nitrogen, thus, contributing to the fertility of agricultural soils worldwide, while others behave as nuisance microorganisms in aquatic ecosystems due to their involvement in toxic bloom events. However, in spite of their ecological importance and environmental concerns, their identification and taxonomy are still problematic and doubtful, often being based on current morphological and physiological studies, which generate confusing classification systems and usually vary under different conditions. In fact,the taxonomy of cyanobacteria has been substantially modified in the last few decades, particularly, after the application of modern ultrastructural and molecular methods. Therefore, the present research aimed to investigate through a polyphasic approach, the differences in morphological and genotypic features of two cyanobacteria strains isolated from paddy fields of Iran, belonging to the family Nostocaceae (subsection IV. I). In the present study, morphometric and genetic (16S rRNA) data were used to characterize the strains in liquid suspension cultures and solid media under photoautotrophic conditions. The heterocytous cyanobacteria form a monophyletic group according to 16S rRNA gene sequence data. Phylogenetic analysis of 16S rRNA indicated that strain FSN_E and ASN_M are parts of the Nostoc cluster. The result was verified with morphological observations. These cyanobacteria are named as Nostoc sp. FSN_E andNostoc sp. ASN_M.
Key words: Cyanobacteria, Nostoc sp. FSN_E, Nostoc sp. ASN_M, hormogonia, phylogenetic analyses, morphological evaluation, 16S rRNA.
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