Glutamate synthase of Corynebacterium glutamicum is not essential for glutamate synthesis and is regulated by the nitrogen status

The Corynebacterium glutamicum gItB and gItD genes, encoding the large (alpha) and small (fi) subunit of glutamate synthase (GOGAT), were investigated in this study. Using RT-PCR, a common transcript of gItB and gItD was shown. Reporter gene assays and Northern hybridization experiments revealed that transcription of this operon depends on nitrogen starvation. The expression of gItBD is under control of the global repressor protein AmtR as demonstrated by gel shift experiments and analysis of gItB transcription in an amtR deletion strain. In contrast to other bacteria, in C. glutamicum GOGAT plays no pivotal role; e.g. gItB and gItD inactivation did not result in growth defects when cells were grown in standard minimal medium and only a slight increase in the doubling time of the corresponding mutant strains was observed in the presence of limiting amounts of ammonia or urea. Additionally, mutant analyses revealed that GOGAT has no essential function in glutamate production by C. glutamicum.