Evaluation of incongruence between traditional classification and phylogenetic relationships based on 16S rDNA sequence of two Nostoc species

Subject Areas : Biotechnology and Applied Microbiology journal

Received: 2017-11-05 Accepted : 2017-11-05 Published : 2014-08-23

Keywords: Morphology, ITS, Cyanobacteria, 16S rRNA, Nostoc,

Abstract :

Studies of cyanobacterial species are important to the global scientific community, mainly, the order, Nostocalesfixes atmospheric nitrogen, and thus, contributing to the fertility of agricultural soils worldwide, while othersbehave 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 taxonomyare still problematic and doubtful, often being based on current morphological and physiological studies, whichgenerate confusing classification systems and usually vary under different conditions. The present researchaimed to investigate through a polyphasic approach, the differences in morphological and genotypic features oftwo cyanobacteria strains isolated from paddy fields of Iran, belonging to the family Nostocaceae (subsection IV.I). Based on the description of the morphology provided by valid keys, two strains were identified as Nostocellipsosporum and Nostoc muscorum. Challenges arise when two Nostoc strains cannot be discriminated by 16SrRNA and ITS genes sequencing. The results of sequencing of the cloned bacterial 16S rRNA fragment stronglyindicated that the current morphological classification of the two Nostoc species is invalid. Moreover,phylogenetic studies of two Nostoc strains have demonstrated that genetic relationships conflict with themorphological classification. We concluded that the two Nostoc strains investigated might possibly be unitedinto one species.