To search for a novel glutamate decarboxylase (GAD) with an optimum pH towards near-neutrality in order to improve production of gamma-aminobutyric acid (GABA) in recombinant hosts. A novel glutamate decarboxylase, BmGAD, from Bacillus megaterium was overexpressed and purified. BmGAD was approximately 53 kDa by SDS-PAGE analysis. Its optimum activity was at pH 5 and 50 A degrees C. BmGAD had a specific activity of 59 +/- A 5.2 U mg(-1) at pH 6, which is the highest value reported so far. The apparent Km and V-max values of BmGAD were 8 +/- A 0.5 mM and 150 +/- A 4.7 U mg(-1), respectively. Through site-directed mutagenesis, two BmGAD mutants (E294R and H467A) showed higher V-max values than that of wild-type, with the values of 210 +/- A 6.9 and 180 +/- A 4.1 U mg(-1) at pH 5 and 50 A degrees C, respectively. The unusual high activity of BmGAD at pH 6 makes it an attractive GABA-producing candidate in industrial application.