EXCRETION OF AMMONIUM BY AZOSPIRILLUM-BRASILENSE MUTANTS RESISTANT TO ETHYLENEDIAMINE

Several spontaneous ethylenediamine-resistant mutants of Azospirillum brasilense strain FP2 (Sp7, Nal(R) Sm(R)) were isolated. Four mutants, HM053, HM14, HM26, and HM210, were found to fix nitrogen constitutively in the presence of high concentration of NH4+ and to excrete NH4+ derived from nitrogen fixation. They also showed lower rates of NH4+ uptake than the wild-type strain, FP2. All of the mutants were prototrophic for glutamine or glutamate. Their glutamate synthase and glutamate dehydrogenase activities were similar to those of the wild-type strain. However, they presented different patterns of glutamine synthetase activity. Mutant HM 14 showed low levels of normally regulated glutamine synthetase activity, while the other mutants showed low levels (HM053) or wild-type levels (HM26 and HM210) of constitutively adenylylated glutamine synthetase activity. The mutants are probably defective in the adenylylation system.