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

Acknoeledgements

We are grateful for the support of the Natural Science Foundation of Fujian Province (2016J05074 and 2014J01037).

Additional information

Funding

This work received financial support from the Natural Science Foundation of Fujian Province under grants number 2016J05074 and 2014J01037.