Synthesis of γ-aminobutyric acid by expressing Lactobacillus brevis-derived glutamate decarboxylase in the Corynebacterium glutamicum strain ATCC 13032.

Purpose of this work is to synthesize γ-aminobutyric acid by glutamate-producing species expressing Lactobacillus brevis-derived glutamate decarboxylase genes, i.e. recombinant Corynebacterium glutamicum strains, which directly convert endogenous L-glutamate precursor into γ-aminobutyric acid (GABA) through single-step fermentation. To express exogenous glutamate decarboxylase (GAD) in an L-glutamate-producing strain, Lactobacillus brevis Lb85, which can produce GABA, was used. Two Lb85 GAD genes, gadB1 and gadB2, and the ancillary genes, gadC-gadB2 and gadR-gadC-gadB2, were cloned separately into pDXW-8 and transformed into C. glutamicum. All four recombinant strains produced GABA whereas the wild-type strain did not. GABA produced by the recombinant strains continually increased after 36 h of fermentation. Although the mRNA levels of LbgadB2 and LbgadC were similar among the corresponding recombinants, GABA production of pDXW-8/gadRCB2 at 72 h (2.15 g/l) was higher than that of pDXW-8/gadCB2 (1.25 g/l) and pDXW-8/gadB2 (0.88 g/l). Thus, by introducing Lbgad genes, C. glutamicum was genetically engineered to synthesize GABA using endogenous L-glutamate.