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 (alp ha) and small (fi) subunit of glutamate synthase (GOGAT), were investigated in this study. Using RT-PCR, a common transcript of gItB and gItD was show n. Reporter gene assays and Northern hybridization experiments revealed tha t transcription of this operon depends on nitrogen starvation. The expressi on of gItBD is under control of the global repressor protein AmtR as demons trated by gel shift experiments and analysis of gItB transcription in an am tR deletion strain. In contrast to other bacteria, in C. glutamicum GOGAT p lays no pivotal role; e.g. gItB and gItD inactivation did not result in gro wth defects when cells were grown in standard minimal medium and only a sli ght increase in the doubling time of the corresponding mutant strains was o bserved in the presence of limiting amounts of ammonia or urea. Additionall y, mutant analyses revealed that GOGAT has no essential function in glutama te production by C. glutamicum.