Efficient gamma-aminobutyric acid bioconversion by engineered Escherichia coli

Abstract

Gamma-aminobutyric acid (GABA) can be converted into 2-pyrrolidone, an intermediate in the synthesis of nylon 4 and agrochemicals, which has great potential for application in the chemical industry. The main aim of this work was to construct a simple and efficient process for industrial production of GABA from L-glutamic acid (L-Glu) by whole-cell bioconversion. The gene encoding glutamate decarboxylase (GAD) from Lactococcus lactis FJNUGA01 was overexpressed using the most available vector in Escherichia coli, pET-28a. GABA production was enhanced by optimizing the concentration of the catalyst isopropyl-β-D-thiogalactoside (IPTG), induction temperature and induction time. After optimization, GABA production reached 98.4 g L−1 with 96 mol% conversion within 6 h was achieved by whole-cell conversion using the cells induced with 1 mmol L−1 IPTG for 12 h at 30 °C. Furthermore, when the initial concentration of L-Glu was adjusted, 204.12 g L−1 GABA with 34 g L−1 h−1 productivity was reached using 2 mol L−1 L-Glu as the substrate. During the 6 h whole-cell bioconversion process, almost all L-Glu was converted to GABA with a conversion efficiency of ∼99%. The high conversion efficiency and high productivity made the GABA purification occur downstream, and the whole process is more simple and economical for industrial application.

Keywords

• Gamma-aminobutyric acid
• glutamate decarboxylase
• whole-cell bioconversion
• Escherichia coli