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Glutamate decarboxylase (GAD) is a main enzyme for biotransformation of L-glutamic acid (L-glu) to gamma-aminobutyric acid (GABA), a component of pharmaceuticals, functional foods, and the biodegradable plastic polyamide 4.This enzyme exhibits an acidic pH optimum (usually pH 4-5), and sharply loses activity at pH 6.However, the expanding activity of GAD at a near-neutral pH will be useful in industry.In the current study, we identified and characterized a homologue of glutamate decarboxylase from Bacillus megatarium.The gene product designated Bm-GAD exhibited homology to enzymes from E.coli and Lactobacillus brevis (50％ and 23％,respectively).Bm-Gad was cloned, overexpressed in E.coli BL21 (DE3), and purified to homogeneity.The purified recombinant Bm-GAD was approximately 53 kDa.The enzyme showed high activity from 45 ℃ to 60 ℃, and it had a maximum specific activity of 154 U/mg at 50 ℃.The optimal pH of the recombinant Bm-Gad was 5.0 at 50℃, however, the enzyme still had high activity at 6.0, with a specific activity of 56.35 U/mg.The enzyme activity could be significantly inhibited by Cu2+, Fe3+ and Fe2+.The apparent Km and Vmax values were 8.69 mmol/Land 153.16 U/mg, respectively.The expanding activity of Ba-GAD at pH 6 makes it better candidate for GABA production in industry.The production of GABA using E.coli whole-cell biocatalysis will be further investigated.