In this study, morphological and microscopic observations were performed along with growth measurements, evaluation of extracellular ammonium and nitrogenase activity. A total of 62 diazotrophic nostocalean cyanobacteria belonging to 12 genera viz- Scytonema (2), Anabaena (22), Nostoc (17), Cylindrospermum (2), Anabaenopsis (1), Dichothrix (1), Tolypothrix (2), Calothrix (6), Aulosira (4), Microchaete (3), Wollea (1) and Rivularia (1) which were originally isolated from different niches of north east India were procured from National fresh water cyanobacterial and microalgal repository of DBT-IBSD, Imphal, Manipur, India. Among the different nostocalean cyanobacteria encountered from the various habitats, Anabaena sp. BTA650, an isolate from lithophytes under running water, Moreh, Chandel, Manipur exhibited highest nitrogenase activity of 111.08±13.26 nmole C2H4 µg-1 Chl-a h-1 can be a potential candidate for biofertilizer formulation particularly for terraced hill rice culture condition.
Key words: Diazotrophs, cyanobacteria, nitrogenase activity, extracellular ammonium, repository, biofertilizer
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