High-level production of γ-aminobutyric acid via efficient co-expression of the key genes of glutamate decarboxylase system in Escherichia coli

•A double promoter PT7lac and PBAD expression system was constructed for tunable control of GadB and GadC overexpression.•Broadening the active pH range of GadB and GadC towards neutral pH improving the GABA productivity.•A high efficient GABA synthesis system using engineered E. coli Lemo21(DE3) cells as the biocatalysts has been developed.