Determinative value of a portion of the nifH sequence for the genera Nostoc and Anabaena (Cyanobacteria)

The taxonomic positions of Nostoc and Anabaena strains are currently disput ed. We selected three Nostoc and Anabaena strains, using the classic criter ia of morphology and life cycle. DNA sequences of a part of the nifH gene w ere determined from these strains and aligned with homologous sequences fro m 10 other Nostoc/Anabaena strains in the public databases. Phylogenetic re constructions were carried out to test the consistency of the taxonomic pla cement of these strains. The phylogenetic trees do not separate these strai ns into distinct groups. Our results are in agreement with other molecular- based phylogenies that also fail to differentiate the Nostoc-Anabaena group s. The data suggest that the currently recognized genera Nostoc and Anabaen a may in fact belong within a single, broadly defined genus.