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Background  Gamma (γ)-Aminobutyric acid (GABA) as a bioactive compound is used extensively in functional foods, pharmaceuticals and agro-industry. It can be biosynthesized via decarboxylation of monosodium glutamate (MSG) or L-glutamic acid (L-Glu) by glutamate decarboxylase (GAD; EC4.1.1.15). GADs have been identified from a variety of microbial sources, such as  Escherichia coli  and lactic acid bacteria. However, no GADs from  Streptomyces  have been characterized. The present study is aimed to identify new GADs from  Streptomyces  strains and establish an efficient bioproduction platform for GABA in  E. coli  using these enzymes.    Results  By sequencing and analyzing the genomes of three  Streptomyces  strains, three putative GADs were discovered, including StGAD from  Streptomyces toxytricini  NRRL 15443, SsGAD from  Streptomyces  sp .  MJ654-NF4 and ScGAD from  Streptomyces chromofuscus  ATCC 49982. The corresponding genes were cloned from these strains and heterologously expressed in  E. coli  BL21(DE3). The purified GAD proteins showed a similar molecular mass to GadB from  E. coli  BL21(DE3). The optimal reaction temperature is 37 °C for all three enzymes, while the optimum pH values for StGAD, SsGAD and ScGAD are 5.2, 3.8 and 4.2, respectively. The kinetic parameters including  V   max  , K m ,  k   cat   and  k   cat  /K m  values were investigated and calculated through in vitro reactions. SsGAD and ScGAD showed high biocatalytic efficiency with  k   cat  /K m  values of 0.62 and 1.21 mM − 1 ·s − 1 , respectively. In addition, engineered  E. coli  strains harboring StGAD, SsGAD and ScGAD were used as whole-cell biocatalysts for production of GABA from L-Glu.  E. coli /SsGAD showed the highest capability of GABA production. The cells were repeatedly used for 10 times, with an accumulated yield of 2.771 kg/L and an average molar conversion rate of 67% within 20 h.    Conclusions  Three new GADs have been functionally characterized from  Streptomyces , among which two showed higher catalytic efficiency than previously reported GADs. Engineered  E. coli  harboring SsGAD provides a promising cost-effective bioconversion system for industrial production of GABA.    Electronic supplementary material  The online version of this article (10.1186/s13036-019-0154-7) contains supplementary material, which is available to authorized users.

Identification of new glutamate decarboxylases from Streptomyces for efficient production of γ-aminobutyric acid in engineered Escherichia coli