Effect of 7-Azatryptophan on Nitrogen Fixation and Heterocyst Formation in the Blue-green Alga Anabaena cylindrica

Abstract

In the blue-green alga Anabaena caienula, 7-azatryptophan was shown to alter the pattern of heterocyst formation in two ways: (a) the number of these specialized cells is increased, (b) groups of adjacent heterocysts are formed. The present communication extends these observations on the morphological changes to the blue-green alga Anabaena cylindrica . Moreover, nitrogen fixation activities are observed to increase parallel with the formation of new heterocysts when Anabaena is grown in the presence of 1—5, µ M azatryptophan indicating that the heterocysts are the main site of nitrogenase in these aerobically grown cultures. Kinetic studies show that azatryptophan first affects nitrogen fixation. This inhibition is followed by an increase in the number of heterocysts and finally by a recovery of the nitrogen fixation activity beyond that of control algae grown without the tryptophan analogue. Azatryptophan specifically inhibits nitrogen fixation in Anabaena, since it does not affect ammonia-grown Anabaena cylindrica or nitrogen fixing Klebsiella pneumoniae .