The response of the nitrogen-fixing cyanobacterium anabaena azollae to combined nitrogen compounds and sugar

Symbiotic Anabaena isolated from the water fern Azolla exhibits properties similar to those of heterocystous free-living cyanobacteria. Anabaena azollae is unique in its capacity of employing fructose for efficient N₂ fixation in the dark. Combined nitrogen compounds are metabolized by A. azollae and are tolerated at low concentrations. Both nitrate and NH⁺₄ affect the biosynthesis of nitrogenase and other proteins. The presence of low NH⁺₄ concentrations, which are tolerated by A. azollae, affects the cell structure and organization.