Identification of gamma-aminobutyric acid (GABA)-producing lactic acid bacteria from plant-based Thai fermented foods and genome analysis of Lactobacillus brevis GPB7-4

Sixteen gamma-aminobutyric acid (GABA)-producing lactic acid bacteria (LAB) strains were isolated from
plant-based Thai fermented foods, such as fermented bamboo shoots (naw-mai-dong), pickled green mustard (phakgard-dong), salted mango (ma-muang-dong), and sweetened radish (hua-chai-po), obtained in Central and Eastern Thailand. These strains were placed in a monophyletic cluster consisting of Lactobacillus, Pediococcus, and Leuconostoc species and divided into seven groups based on phenotypic characteristics and 16S rRNA gene sequences. Eleven rod-shape strains of Lactobacillus were identified as L. brevis (Group I, 6 strains), L. pentosus (Group II, 2 strains), L. fermentum (Group III, 2 strains), and L. plantarum (Group IV, 1 strain). Two tetrad-forming strains of Pediococcus were identified as P. acidilactici (Group V, 1 strain) and P. pentosaceus (Group VI, 1 strain). In addition, three coccus chain bacteria were identified as Leuconostoc mesenteroides (Group VII, 3 strains). The produced GABA from the 16 strains ranged from 0.760.02 to 13.420.28 g/l. Among them, L. brevis GPB7-4 (Group I) gave the highest level of GABA production at 13.420.28 g/l from 30 g/l monosodium glutamate (MSG) when cultivated at 30 °C for 72 h. Based on genome analysis, the GPB7-4 strain was closely related to L. brevis ATCC 367 with an ANIb value of 99.94%. The strain consisted of the complete genes of GABA producer gadA and gadB indicating its ability to produce GABA, thus it is a promising candidate for fermented food applications.