Nitrogen and carbon regulation of glutamine synthetase and glutamate synthase in Corynebacterium glutamicum ATCC 13032

Abstract

The effect of nitrogen and carbon status on the regulation of glutamine synthetase (GS) and glutamate synthase (GOGAT) were investigated in Corynebacterium glutamicum 13032. Under carbon-sufficient, nitrogen-limiting conditions, GS and GOGAT activities were five-and seven-fold higher, respectively, and transcription of the corresponding genes (glnA and gltBD) was similarly induced. GS activity was also induced in complete medium with added glucose, while GOGAT activity was unaffected. Under carbon-limiting, nitrogen-limiting conditions, the level of GS induction was reduced approximately three-fold, whereas GOGAT activity did not respond. Disruption of the hkm gene, encoding a putative histidine kinase upstream of gltBD, reduced the levels of GOGAT activity two-fold under both nitrogen-rich and nitrogen-limiting conditions. Promoter studies using a hkm^chloramphenicol acetylase fusion plasmid revealed that transcription of hkm is moderately induced (ca. 1.5-fold) by nitrogen starvation, indicating that the Hkm protein may play a role in signal transduction of the nutritional status of the growth medium. ß

Regulation of nitrogen metabolism in Mycobacterium tuberculosis: A comparison with mechanisms in Corynebacterium glutamicum and Streptomyces coelicolor

“…Thus, GOGAT is not directly regulated at the level of enzyme activity in either C. glutamicum, or M. tuberculosis (8). Under conditions of nitrogen limitation, the activity of GOGAT in C. glutamicum increased 7-fold which corresponded particularly well with an increase in gltBD (operon encoding the large, gltB, and small, gltD, subunits of GOGAT) transcription (8). In the absence of posttranslational modification, the activity of GOGAT is therefore regulated at the transcriptional level.…”

“…In contrast, there has been thus far, no report of posttranslational modification of GOGAT in response to changing nitrogen conditions. Thus, GOGAT is not directly regulated at the level of enzyme activity in either C. glutamicum, or M. tuberculosis (8). Under conditions of nitrogen limitation, the activity of GOGAT in C. glutamicum increased 7-fold which corresponded particularly well with an increase in gltBD (operon encoding the large, gltB, and small, gltD, subunits of GOGAT) transcription (8).…”

“…The low ammonium affinity GDH pathway is preferentially utilized when nitrogen availability is high and Glu is produced through reversible amination of 2-oxoglutarate (8). In contrast, the high affinity GS/GOGAT pathway is utilized under nitrogen-limiting conditions.…”

Metabolic analysis of Chlorobium chlorochromatii CaD3 reveals clues of the symbiosis in ‘Chlorochromatium aggregatum’

“…Both mechanisms are regulated by nitrogen availability. The GS/GOGAT pathway is a high-affinity mechanism that is active when there is low availability of nitrogen, and in the case of diazotrophic bacteria, when they are fixing nitrogen (Rudnick et al, 1997;Schulz et al, 2001). On the contrary, the assimilation of ammonia by GDH is a mechanism of low affinity that is active when there is high availability of nitrogen (Brown and Herbert, 1977;Rudnick et al, 1997).…”

Mutation-induced metabolite pool alterations in Corynebacterium glutamicum: Towards the identification of nitrogen control signals

“…Assimilation via glutamate dehydrogenase is bioenergetically more favourable, as the GS/GOGAT pathway utilizes an additional mol ATP per mol ammonium assimilated. Consequently, GDH is preferentially used in ammonium-rich medium, while transcription of gltBD, coding for GOGAT, is completely repressed in this situation (Beckers et al, 2001;Schulz et al, 2002) and transcription of glnA, coding for GS, is maintained at a basal level to provide l-glutamine for growth (Nolden et al, 2001a). When the cells face nitrogen limitation, assimilation via GDH is not sufficient due to the low affinity of the enzyme.…”