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Glutamate excretion as a major kinetic bottleneck for the thermally triggered production of glutamic acid by Corynebacterium glutamicum.

The study was aimed at evaluating the extent of flux control exercised by the amino acid excretion step on the glutamate production flux in C. glutamicum 2262 strain that is induced for glutamate excretion by an upward temperature shift. Cells initially induced to excrete glutamate were cultivated at different controlled temperatures between 33 and 40 degrees C, and changes in glutamate excretion flux and intracellular concentration were determined in response to increased culture temperature. The fastest growth rate of 0.45 h(-1) and the lowest glutamate excretion rate of 1 mmole/g dw x h were observed at 33 degrees C, together with a high intracellular 0.5 mmole/g dw glutamate accumulation. On the contrary, the fastest glutamate excretion rate of 6 mmole/g dw x h was obtained at 40 degrees C, when cell growth was arrested and the internal glutamate level reduced to 0.25 mmol/g dw. The observed sixfold increase in excretion flux as a result of the temperature increase clearly suggests a specific effect of temperature on the glutamate export system which appears as the major kinetic bottleneck for the glutamate production flux. This conclusion is corroborated by the high internal accumulation of glutamate which, even under the fastest excretion conditions, severely inhibits the activity of the glutamate biosynthesis pathway.