Physiological Characterization of the Ammonium Transport System in the Free-living Diazotrophic Cyanobacterium Anabaena cycadeae

The methylammonium (ammonium) transport activity in both the parental and glutamine synthetase-deficient mutants strains of Anabaena cycadeae was found to be characteristically active, energy requiring, and biphasic with a fast initial phase followed by a relatively slower second phase. The persistance of the biphasic pattern of the ammonium transport process in the absence of glutamine synthetase activity in the mutant strain suggests that it does not play a role in controlling methylammonium (ammonium) uptake in this cyanobacterium. The methyl-ammonium (ammonium) transport activity remained sensitive to methionine sulfoximine (MSX) inhibition in both the strains, thereby suggesting methylammonium (ammonium) transport activity to be specially sensitive to direct action of MSX. The methylammonium (ammonium) transport activity was found to be repressible and derepressible, suggesting the involvement of «nitrogen regulation» system. Derepression of ammonium transport activity was found to require de novo protein synthesis and was inhibited by glutamine. Repression did not require any de novo protein synthesis.