Enhancement of γ-aminobutyric acid production in recombinant Corynebacterium glutamicum by co-expressing two glutamate decarboxylase genes from Lactobacillus brevis

gamma-Aminobutyric acid (GABA), a non-protein amino acid, is a bioactive component in the food, feed and pharmaceutical fields. To establish an effective single-step production system for GABA, a recombinant Corynebacterium glutamicum strain co-expressing two glutamate decarboxylase (GAD) genes (gadB1 and gadB2) derived from Lactobacillus brevis Lb85 was constructed. Compared with the GABA production of the gadB1 or gadB2 single-expressing strains, GABA production by the gadB1-gadB2 co-expressing strain increased more than twofold. By optimising urea supplementation, the total production of l-glutamate and GABA increased from 22.57 +/- A 1.24 to 30.18 +/- A 1.33 g L-1, and GABA production increased from 4.02 +/- A 0.95 to 18.66 +/- A 2.11 g L-1 after 84-h cultivation. Under optimal urea supplementation, l-glutamate continued to be consumed, GABA continued to accumulate after 36 h of fermentation, and the pH level fluctuated. GABA production increased to a maximum level of 27.13 +/- A 0.54 g L-1 after 120-h flask cultivation and 26.32 g L-1 after 60-h fed-batch fermentation. The conversion ratio of l-glutamate to GABA reached 0.60-0.74 mol mol(-1). By co-expressing gadB1 and gadB2 and optimising the urea addition method, C. glutamicum was genetically improved for de novo biosynthesis of GABA from its own accumulated l-glutamate.