Effect of Glutamate Concentration and Atmosphere of Incubation on the Production of ɣ-Aminobutyric Acid in Levilactobacillus brevis LB12

Levilactobacillus brevis is able to produce ɣ-aminobutyric acid (GABA), a non-proteogenic amino acid that provides several benefits to human health. In this study, we investigated the effect of glutamate (Glu) and oxygen (O2) on biomass yield, GABA production and regulation of the gad operon in Lvb. brevis LB12. A change in incubation atmosphere from anaerobiosis (AN) to aerobiosis (AE) was applied to elucidate if AE pre-adaptation and cultivation could be exploited to improve cell density, as well as to determine the role of O2 on the expression of the gad operon. AE increased biomass yield, but impaired Glu to GABA conversion, in both the cultivation and the adaptation phases. The gad operon (gadR, gadC, gadB, gltX) was up-regulated in the presence of Glu, while O2 strongly reduced the transcription of gadC and gadB. Switching the incubation atmosphere (AE vs. AN) and Glu supplementation did not restore the gene functionality, suggesting that the negative effect of O2 was persistent and more prolonged adaptation to AN would be required. This study provides additional data on the regulation of the gad operon, but further insight on the effect of O2 upon GABA production by Lvb. brevis must be expanded to understand the possible mechanisms involved.