NITROGEN-FIXATION AND HYDROGEN UPTAKE IN 4 CYANOBACTERIA

Anabaena variabilis, Nostoc spongiaeforme, Westiellopsis prolifica, and Nostoc sp. isolated from diverse local habitats fixed nitrogen under aerobic conditions, but the nitrogenase activity was greater in anaerobic conditions. Nitrogenase activity was highest in fluorescent light in the case of A. variabilis, W. prolifica and Nostoc sp., but that of N. spongiaeforme was higher in incandescent light. N. spongiaeforme showed high nitrogenase activity in blue light also, whereas the other three species had stronger activity in red light than in blue light. A concentration of H-2 up to 20% enhanced the nitrogenase activity, but 25% was inhibitory in all of the four organisms. All the four strains were found capable of utilizing exogenous hydrogen. N. spongiaeforme showed higher H-2 uptake activity both under aerobic and anaerobic conditions and its capacity for chromatic adaptation may partly account for such behaviour. Addition of DCMU inhibited hydrogen uptake in A. variabilis, W. prolifica and Nostoc sp. but not in N. spongiaeforme.