Fatty acids synthesis in vivo and antioxidation level regulated ?-aminobutyric acid production in Lactobacillus brevis, elucidated by supplementation of cysteine

Lactobacillus brevis NPS-QW 145 isolated from kimchi is deficient in glutamate dehydrogenase-encoding gene (gdhA) to form glutamate, hence it required exogenous supplementation of glutamate/monosodium glutamate (MSG) for decarboxylation reaction to produce ?-aminobutyric acid (GABA). However, GABA conversion rate was low in the presence of MSG. Cysteine was selected among 21 amino acids to significantly improve GABA conversion from MSG. Subsequently, RP-HPLC, transcriptomics and RT-PCR were combined to understand the mechanism behind cysteine in improving GABA production in Lb. brevis. Cysteine was found to protect cells against oxidative damage caused by H2O2 and increased cell density of Lb. brevis for increased GABA production. Moreover, cysteine promoted the glycolysis to produce acetyl-CoA for synthesizing fatty acids to significantly up-regulate GABA biosynthesis. However, the mechanism behind fatty acids synthesis and GABA production needs to be further explored. These findings deciphered antioxidative capability of cysteine in Lb. brevis 145 and provided a theoretical basis for fatty acids synthesis-mediated GABA synthesis in Lb. brevis 145 and possibly in other lactic acid bacteria.