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Background  In lactic acid bacteria (LAB), acid stress leads to decreases of cell vitality and fermentation yield. Glutamate decarboxylase (GAD) system is regarded as one of the essential acid-resistance mechanisms in LAB. However, the regulation of GAD system is not well identified in the genus  Lactobacillus . Although potential transcriptional regulator gene located upstream of GAD system genes was found in several  Lactobacillus  species, such as  Lactobacillus  ( L. )  brevis , the contribution of the regulator to acid resistance of the genus  Lactobacillus  has not been experimentally determined.    Results  The potential transcriptional regulator gene  gad R was disrupted by homologous recombination in  L. brevis  ATCC 367, leading to the decreased expression of  gad C and  gadB . The inactivation of GadR completely eliminated γ-aminobutyric acid (GABA) production and decreased the glutamate-dependent acid resistance. Moreover, expression of  gad C and  gad B in the presence of glutamate was increased and glutamate also stimulated the expression of  gad R. In addition,  L. brevis  D17, a strain screened from acidic fermented grains of Chinese liquor production, had much higher expression level of  gad R than the typical strain  L. brevis  ATCC 367. Under the pH-controlled and mixed-feed fermentation,  L. brevis  D17 achieved a titer of 177.74 g/L and a productivity of 4.94 g/L/h of GABA within 36 h. However, the  L. brevis  ATCC 367 only achieved a titer of 6.44 g/L and 0.18 g/L/h of GABA although the same fermentation control approach was employed.    Conclusions  GadR is a positive transcriptional regulator controlling GABA conversion and acid resistance in  L. brevis .  L. brevis  strains with hyper-expressing of  gad R are excellent candidates for GABA production in industrial scale.    Electronic supplementary material  The online version of this article (10.1186/s12934-019-1157-2) contains supplementary material, which is available to authorized users.

Deciphering the crucial roles of transcriptional regulator GadR on gamma-aminobutyric acid production and acid resistance in Lactobacillus brevis