In situ biotransformation of synthetic glutamate to γ-amino butyric acid by an auxotrophic Lactococcus lactis in polysorbate-mediated thermoaerobic process.

This study focused on the in situ biotransformation to γ-aminobutyric acid (GABA) from synthetic glutamate using a specialized Lactococcus lactis strain that is auxotrophic, facilitated by a polysorbate-assisted thermoaerobic fermentation approach. Physical mutagenesis was applied in the wild-type ISL-7 strain using ultraviolet (UV) light, and various experimental conditions were explored, including different concentrations of L-tryptophan (0.005 to 0.03%, w/v), ultraviolet exposure times (5 to 30 min), and distances (5 to 30 cm). Out of 34 mutant strains evaluated for their ability to produce GABA, mutant strain, named UV-L-cys-3, demonstrated notably enhanced GABA synthesis (137.70 ± 6.88 mM) in contrast to the wild type ISL-7 strain, which produced 24.36 ± 1.22 mM. Fermentation conditions using monosodium glutamate (MSG) as the primary substrate were subsequently optimized for both the wild-type and mutant strains under submerged cultivation. The wild-type strain produced 214.36 ± 10.71 mM GABA at 30 °C with 45 min of reaction time in a medium containing 1.25% yeast extract, 1.5% MSG, and 10% glucose at a pH of 7.2. In contrast, the UV-L-cys-3 strain achieved a basal optimal yield of 344.36 mM GABA in a medium with 1% yeast extract, 1% MSG, and 4% glucose under its optimal conditions. Additionally, the effects of various reaction mediators and growth stimulators including L-ascorbic acid, methanol, and polysorbate were assessed. Methanol and polysorbate significantly enhanced GABA production, yielding peak concentrations of 260.36 and 450.03 mM in ISL-7 and UV-L-cys-3, respectively. L-ascorbic acid was found to have an inhibitory effect on GABA yield under the tested conditions. The UV-L-cys-3 mutant strain exhibited a significant improvement, producing 1.73 times more GABA than the wild-type strain, with high statistical significance (p ≤ 0.05), indicating its promising potential for scale-up and industrial-level GABA production applications.

© 2026. The Author(s), under exclusive licence to Springer Nature B.V.