C-13 NMR-STUDIES OF THE FLUXES IN THE CENTRAL METABOLISM OF CORYNEBACTERIUM-GLUTAMICUM DURING GROWTH AND OVERPRODUCTION OF AMINO-ACIDS IN BATCH CULTURES

The carbon flux distribution in the central metabolism of Corynebacter ium glutamicum was studied in batch cultures using [1-C-13]- and [6-C- 13]glucose as substrate during exponential growth as well as during ov erproduction of L-lysine and L-glutamate. Using the C-13 NMR data in c onjunction with stoichiometric metabolite balances, molar fluxes were quantified and normalised to the glucose uptake rate, which was set to 100. The normalised molar flux via the hexose monophosphate pathway w as 40 during exponential growth, whereas it was only 17 during L-gluta mate production. During L-lysine production, the normalised hexose mon ophosphate pathway flux was elevated to 47. Thus, the carbon flux via this pathway correlated with the NADPH demand for bacterial growth and L-lysine overproduction. The normalised molar flux in the tricarboxyl ic acid cycle at the level of 2-oxoglutarate dehydrogenase was 100 dur ing exponential growth and 103 during L-lysine secretion. During L-glu tamate formation, the normalised flux through the tricarboxylic acid c ycle was reduced to 60. In contrast to earlier NMR studies with C. glu tamicum, no significant activity of the glyoxylate pathway could be de tected. All experiments indicated a strong in vivo flux from oxaloacet ate back to phosphoenolpyruvate and/or pyruvate, which might be due to phosphoenolpyruvate carboxykinase activity in C. glutamicum.