Substrate sustained release-based high efficacy biosynthesis of GABA by Lactobacillus brevis NCL912

Abstract

Background: Gamma-aminobutyric acid (GABA) plays a significant role in the food and drug industries. Our previous study established an efficient fed-batch fermentation process for Lactobacillus brevis NCL912 production of GABA from monosodium l-glutamate; however, monosodium l-glutamate may not be an ideal substrate, as it can result in the rapid increase of pH due to decarboxylation. Thus, in this study, l-glutamic acid was proposed as a substrate. To evaluate its potential, key components of the fermentation medium affecting GABA synthesis were re-screened and re-optimized to enhance GABA production from L. brevis NCL912. Results: The initial fermentation medium (pH 3.3) used for optimization was: 50g/L glucose, 25g/L yeast extract, 10mg/L manganese sulfate (MnSO4.H2O), 2g/L Tween-80, and 220g/L l-glutamic acid. Glucose, a nitrogen source, magnesium, and Tween-80 had notable effects on GABA production from the l-glutamic acid-based process; other factors showed no or marginal effects. The optimized levels of the four key components in the fermentation medium were 25g/L glucose, 25g/L yeast extract FM408, 25mg/L MnSO4.H2O, and 2g/L Tween-80. A simple and efficient fermentation process for the bioconversion of GABA by L. brevis NCL912 was subsequently developed in a 10L fermenter as follows: fermentation medium, 5L; glutamic acid, 295g/L; inoculum, 10% (v/v); incubation temperature, 32°C; and agitation, 100rpm. After 48h of fermentation, the final GABA concentration increased up to 205.8±8.0g/L. Conclusions:l-Glutamic acid was superior to monosodium l-glutamate as a substrate in the bioproduction of GABA. Thus, a high efficacy bioprocess with 205g/L GABA for L. brevis NCL912 was established. This strategy may provide an alternative for increasing the bioconversion of GABA.