ISOLATION AND CHARACTERIZATION OF RAPIDLY-GROWING, MARINE, NITROGEN-FIXING STRAINS OF BLUE-GREEN-ALGAE

Five strains of heterocytous blue-green algae capable of high rates of growth and nitrogenase activity were isolated from shallow coastal environments. Growth of the organisms was characterized with respect to temperature, NaCl concentration in the medium and N source. The temperature optima ranged from 35-42.degree. C and all but 1 of the strains displayed a requirement for added NaCl. The generation times under N2-fixing conditions were 5.1-5.9 h and were as low as 3.4 h for growth on NH4Cl. Nitrogenase activity (C2H2 reduction) was high throughout the logarithmic growth phase of each strain. The maximum value observed for 1 strain was 65.5 nmol C2H4 produced/mg protein .times. min and the average values for the 5 strains ranged from 24.5-46.7 nmol C2H4/mg protein .times. min. The organisms all belong to the genus Anabaena. The growth and nitrogenase activity of these strains are much higher than those of the heterocystous blue-green algae commonly used for investigation of N metabolism; they should be useful physiological tools. Their prevalence, as judged by the ease of their enrichment and isolation, in bay and estuarine environments suggests that they are important contributors of combined N.