Ammonia assimilation in Corynebacterium glutamicum and a glutamate dehydrogenase-deficient mutant

In the wild-type of Corynebacterium glutamicum, the specific activity of glutamate dehydrogenase (GDH) remained constant at 1.3 U (mg protein)(-1) when raising the ammonia (NH(4)(+)) concentration in the growth medium from 1 to 90 mM. In contrast, the glutamine synthetase (GS) and glutamate synthase (GOGAT) activities decreased from 1.1 U (mg protein)(-1) and 42 mU (mg protein)(-1), respectively, to less than 10 % of these values at NH(4)(+) concentrations > 10 mM suggesting that under these conditions the GDH reaction is the primary NH(4)(+) assimilation pathway. Consistent with this suggestion, a GDH-deficient C. glutamicum mutant showed slower growth at NH(4)(+) concentrations greater than or equal to 10 mM and, in contrast to the wild-type, did not grow in the presence of the GS inhibitor methionine sulfoximine.