GlnR positively affects the acid resistance of Lactiplantibacillus plantarum from wine by regulating glutamate metabolism

Introduction Owing to its remarkable capacity to modify the aroma profile of wine, Lactiplantibacillus plantarum ( L. plantarum ) derived from wine has emerged as a potential starter for malolactic fermentation. However, the inadequate acid resistance of this bacterium severely restricts its application. In some bacterial species, GlnR is considered a universal transcriptional regulator in response to acid stress. Methods In this study, we determined the function of GlnR in the acid resistance of L. plantarum for the first time. RT-qPCR and yeast one-hybrid assays revealed a direct regulatory correlation between GlnR and genes associated with the glutamate metabolic pathway. Metabolomics analysis via liquid chromatography-mass spectrometry and fermentation studies confirmed that GlnR affected γ-aminobutyric acid (GABA) production. Results The growth and survival rate of the knockout strain XJ25-Δ glnR were significantly lower than those of the wild-type strain XJ25. GlnR can directly bind to the promotor regions of the genes glnA , gadB , and glms1 , thereby upregulating gadB transcription while downregulating glnA and glms1 transcription, directing the increased metabolic flux toward GABA synthesis. Discussion We present evidence that GlnR plays a vital role in the glutamate metabolic pathway and is a positive transcriptional regulator that can control the acid resistance of L. plantarum XJ25. Although GlnR interacts with glnA , gadB , and glms1 , additional studies are warranted to determine how this interaction affects its acid resistance.