Effect of carbon source availability and growth phase on expression of Corynebacterium glutamicum genes involved in the tricarboxylic acid cycle and glyoxylate bypass.

The effect of different carbon sources on the expression of tricarboxylic acid (TCA) cycle genes, along with glyoxylate bypass genes, in Corynebacterium glutamicum was determined. All TCA cycle genes were coordinately expressed in medium containing acetate. Growth in the presence of acetate gave rise to abundant expression of most TCA cycle genes, with the level of gltA transcript being the highest. However, when the cells entered the stationary phase triggered by acetate exhaustion, all genes were repressed, except sucCD and mdhB, which were slightly induced. Acetate withdrawal from the growth medium during the exponential phase also led to rapid repression of most TCA cycle genes and a corresponding twofold increase in the expression of sucCD, which were strongly induced by citrate and succinate. In addition, glucose depletion during the stationary phase led to a corresponding 8-20-fold induction of the sucCD, aceA and aceB genes. Addition of glucose to acetate medium resulted in about 10-fold induction of sucCD. The strong dependence of TCA cycle sucCD and glyoxylate bypass aceA and aceB expression on carbon source availability was confirmed and the regulatory system will be studied precisely.