Effect of glutamate on GABA production by C. glutamicum GAD. To examine the effect of adding L-glutamate during GABA fermentation, C. glutamicum GAD was cultured in 20 mL GP2 medium containing 25 μg mL−1 kanamycin in a shaker flask at 30°C for 96 hours. At 24 hours, 1.0 g L−1 (triangle) or 2.0 g L−1 (circle) of L-glutamate was added to the culture. GP2 medium without glutamate (diamond) served as a control. A: Extracellular GABA (solid line) and glucose (dotted line) levels in each flask were monitored for 96 hours. B: Extracellular glutamate production by C. glutamicum GAD in each flask was monitored throughout the fermentation. Data are expressed as the mean and standard error from three independent experiments.