Gamma-aminobutyric acid (GABA) plays a key role as an inhibitory neurotransmitter in the mammalian sympathetic nervous system and has other health benefits. Molecular characterization, genome analysis, and optimization were investigated to improve GABA production of a selected strain of lactic acid bacteria. Eleven isolates from plant materials were screened for GABA productivity and were identified based on phenotypic and genotypic characteristics. The most potent strain was chosen for genome analysis and GABA production optimization using the response surface methodology (RSM). Each of the two strains was closely related to Lactobacillus plantarum, Lactobacillus brevis, Weissella cibaria, Leuconostoc pseudomesenteroides while each strain was similar to Lactobacillus pentosus, Enterococcus lactis, and Leuconostoc mesenteroides. They produced GABA ranging from 0.036 ± 0.000 to 17.315 ± 0.171 g/L at 72 h-cultivation. Among them, the most potent strain, SL9-6, showed the highest GABA production (17.315 g/L) when cultivated with 10% (v/v) inoculum for 48 h. The draft genome sequence of strain SL9-6 exhibited 96.90% average nucleotide identity value and 74.50% digital DNA-DNA hybridization to Lactobacillus brevis NCTC 13768T. This strain contained a glutamate decarboxylase gene system (gadA, gadB, and gadC). Optimal culture conditions were determined as 40.00 g/L glucose, 49.90 g/L monosodium glutamate, pH 5.94, and 31.10°C by RSM, giving maximum GABA production of 32.48 g/L. Results from RSM also indicated that monosodium glutamate concentration, pH, and temperature were significant variables. GABA production significantly improved here could promise further application of strain SL9-6.
Keywords: Lactobacillus brevis; gamma-aminobutyric acid; glutamate decarboxylase gene; lactic acid bacteria; response surface methodology; silage.