An L-methionine—D,L-sulfoximine-resistant mutant of the cyanobacterium Nostoc muscorum showing inhibitor-resistant γ-glutamyl-transferase, defective glutamine synthetase and producing extracellular ammonia during N2 fixation

AbstractThe role of γ-glutamyl-transferase in regulation of N2-fixation and ammonia assimilation in Nostoc muscorum was examined by isolating mutants in which the enzyme was resistant to L-methionine—D,L-sulfoximine. Mutant and wild-type were compared with respect to nitrogenase activity, extracellular production of nitrogenase-catalysed ammonia, γ-glutamyl-transferase activity and growth in N2 and glutamine media. While the production of inhibitor-resistant enzyme with defective γ-glutamyl-transferase activity fully explains the inhibitor-resistant growth phenotype, the present results also suggest close metabolic linkage between γ-glutamyl transferase, nitrogenase and assimilation and extracellular production of N2-derived ammonia