Heterotrophic micro- and macrocultures of a nitrogen-fixing cyanobacterium.

Anabaena variabilis can be cloned in the dark from fragments with one and few cells, with an efficiency of about 40%, on the nitrogen-free medium of Allen and Arnon solidified with 0.5% agarose and supplemented with 5 mM fructose. The organism can be grown exponentially (tau2 approximately or equal to 36 h) in fermentor cultures in the dark, fixing N2, to a density of greater than 10 g dry weight/l.