Specific γ-aminobutyric acid decomposition by gabP and gabT under neutral pH in recombinant Corynebacterium...

Corynebacterium glutamicum that expresses the exogenous L-glutamate decarboxylase (GAD) gene can synthesize γ-aminobutyric acid (GABA). To prevent GABA decomposition in the recombinant C. glutamicum GAD strain, GABA uptake and the GABA shunt pathway were blocked.

GABA uptake is catalyzed by GABA permease encoded by gabP. The first reaction of the GABA shunt pathway is catalyzed by the GABA transaminase encoded by gabT. Initially, the effects of pH on GABA decomposition in recombinant C. glutamicum co-expressing two GAD genes (gadB1 and gadB2) were analyzed, demonstrating that GABA could be decomposed under neutral pH. Next, the gabP and gabT were individually deleted, and the GABA production of the related GAD strains was investigated by controlling the pH of the final fermentation stage at a neutral state. During this stage, the GABA concentration of the gabT-deleted GAD strain decreased from 23.9 ± 1.8 to 17.7 ± 0.7 g/l. However, the GABA concentration of the gabP-deleted GAD strain remained at 18.6-19.4 g/l.

This study demonstrated that GABA was decomposed under neutral pH and that the deletion of gabP could effectively alleviate GABA decomposition in C. glutamicum.