Characterization of three glutamate decarboxylases from Bacillus spp. for efficient γ-aminobutyric acid production

Background: Gamma-aminobutyric acid (GABA) is an important bio-product used in pharmaceuticals and functional foods and as a precursor of the biodegradable plastic polyamide 4. Glutamate decarboxylase (GAD) converts L-glutamate (L-Glu) into GABA via decarboxylation. Compared with other methods, develop a bioconversion platform to produce GABA is of considerable interest for industrial use. Results: Three GAD genes were identified from three Bacillus strains and heterologously expressed in Escherichia coli BL21 (DE3). The optimal reaction temperature and pH values for three enzymes were 40 degrees C and 5.0, respectively. Of the GADs, GADZ11 had the highest catalytic efficiency towards l-Glu (2.19 mM(- 1) s(- 1)). The engineered E. coli strain that expressed GADZ11 was used as a whole-cell biocatalyst for the production of GABA. After repeated use 14 times, the cells produced GABA with an average molar conversion rate of 98.6% within 14 h. Conclusions: Three recombinant GADs from Bacillus strains have been conducted functional identification. The engineered E. coli strain heterologous expressing GADZ1, GADZ11, and GADZ20 could accomplish the biosynthesis of L-Glu to GABA in a buffer-free reaction at a high L-Glu concentration. The novel engineered E. coli strain has the potential to be a cost-effective biotransformation platform for the industrial production of GABA.