Effect of gadB and gdh Co-expression on Bacterial γ-aminobutyric Acid Production

This study aimed to create a genetically engineered bacterium that could produce γ-aminobutyric acid (GABA) directly from glucose without exogenous L-glutamic acid (L-Glu).The gadB and gdh genes responsible for the generation of two critical enzymes, glutamic acid decarboxylase (GAD) and glutamate dehydrogenase (GDH), respectively, in the synthesis of plant lactobacillus GABA were co-expressed in a Glu-producing strain of Corynebacterium glutamicum, SF016.The resulting effects on GABA production by the recombinational strain, SF016-pgg, were analyzed. The activities of GAD and GDH in SF016-pggnearly doubled after incubation in a shaking flask for 40 h reaching 0.63 mol·min^-1·g^-1 and 0.131 mol·min^-1·g^-1, respectively. Furthermore, the SF016-pgg production of GABA from glucose as a single carbon source totaled 23.12 g·L^-1 in a 40 h fermentation in a tank. The results seemed to clearly demonstrate the effectiveness of the gadB and gdh co-expressed recombinant strain on producing GABA by converting glucose without exogenous addition of L-Glu. As a result, the GABA production cost was significantly reduced making the industrialization of food, feed and/or pharmaceutical applications exceedingly promising.