Production of γ-aminobutyric acid by Levilactobacillus brevis: basic aspects and applications in foods

Gamma-aminobutyric acid (GABA) is a non-proteinogenic amino acid, widely recognized as the main inhibitory neurotransmitter in the mammalian central nervous system. GABA exerts several physiological effects, including antihypertensive, antidiabetic, anxiolytic, and anti-inflammatory activities, making it a promising bioactive compound for the formulation of functional foods. The natural concentration of GABA in foods is relatively low, and chemical synthesis, although efficient, rely on toxic reagents and is unsuitable for food-grade applications. Consequently, microbial fermentation (mainly by using lactic acid bacteria, LAB), has recognised as a sustainable and safe strategy for GABA production. This Ph.D. thesis focuses on the production of GABA by Levilactobacillus brevis LB12, a LAB strain isolated from sourdough, in order to elucidate the physiological, molecular, and genomic factors underlying its ability to synthetise GABA. The research activities integrate cultivations in different growth conditions (i.e. glutamate supplementation, pH, oxygen), stress response, gene expression analysis, and whole-genome sequencing to provide a comprehensive understanding of GABA biosynthesis and its functional role in microbial robustness.