Development of a highly efficient microbial fermentation process of recombinant Escherichia coli for GABA production from glucose

This study was aimed to develop a highly productive microbial fermentation process for gamma-aminobutyric acid (GABA) production from glucose. For this, an efficient GABA-producing E. coli strain was firstly developed through metabolic engineering with a strategy of increasing the flux of GABA biosynthetic pathway and deleting or repressing the GABA shunt pathways that compete with GABA biosynthesis. According to this strategy, three metabolically engineered E. coli strains of GTB, GTS, and A1S1 were constructed, and through batch cultivation of these strains, E. coli GTS was ultimately selected as the most efficient GABA-producing strain. From flask cultures, E. coli GTS was found to produce 3.96 g/L of GABA, a titer 2.1 times or 17 % higher than that produced by E. coli GTB or E. coli A1S1, respectively. To maximize GABA production from glucose, pH-stat fed-batch culture conditions of the E. coli GTS were optimized in a one-factor-at-a-time manner. Fed-batch cultivation of the E. coli GTS under optimal conditions resulted in the highest GABA production performance with a concentration of 85.9 g/L and a volumetric productivity of 2.37 g/L/h. This result shows that the microbial fermentation process developed in this study has outstanding potential for the mass production of GABA.