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 (NH4) 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 NH4 concentrations > 10 mM suggesting that under these conditions the GDH reaction is the primary NH4 assimilation pathway. Consistent with this suggestion, a GDH-deficient C. glutamicum mutant showed slower growth at NH4 concentrations 10 mM and, in contrast to the wild-type, did not grow in the presence of the GS inhibitor methionine sulfoximine. © Rapid Science Ltd. 1998