Fructose-enhanced development and growth of the n₂-fixing cyanobiont anabaena azollae

Fructose supported the heterotrophic growth of the cyanobiont Anabaena azollae, isolated from the water fern Azolla filiculoides, and also enhanced its growth in the light by 2-3-fold. Fructose was taken up at a high rate in the light and in the dark, in an energy-dependent reaction. The photosynthetic and respiratory activities of the fructose grown cells were modified: 0 2 evolution in vivo was decreased by 40%, while PS I activity and dark respiration were 2-3-fold higher than in autotrophically grown cells. These changes were accompanied by 2-3-fold increase in heterocyst differentiation and by a 4-fold stimulation of nitrogenase activity.