Genome sequences and functional analysis of Levilactobacillus brevis LSF9-1 and Pediococcus acidilactici LSF1-1 from fermented fish cake (Som-fak) with gamma-aminobutyric acid (GABA) production

Gamma-aminobutyric acid (GABA) is a crucial inhibitory neurotransmitter in the sympathetic nervous system that exerts regulatory effects on the blood, immune, and nervous systems. GABA production in som-fak , a traditional fermented fish of Thailand, has been attributed to the activity of lactic acid bacteria (LAB). The present study aims to characterize the LAB isolates and compare the genomes and GABA synthesis genes of selected isolates capable of GABA production. Thirteen isolates demonstrating GABA synthesis capability were identified based on their phenotypic and genotypic characteristics. Seven isolates (group I: LSF3-3, LSF8-3, LSF9-1, LSF9-3, LSF9-6, LSF9-7, and LSF10-14) were identified as Levilactobacillus brevis with 99.78–100% similarity. LSF2-1, LSF3-2, LSF5-4, and LSF6-5 (group II) were identified as Lactiplantibacillus pentosus with 99.86–100% similarity. Strain LSF1-1 (group III) was identified as Pediococcus acidilactici (99.47%), and LSF10-4 (group IV) was identified as Pediococcus pentosaceus with 99.93% similarity. The GABA production of isolates ranged from 0.087 to 16.935 g/L. The maximum production of 16.935 g/L from 3% monosodium glutamate was obtained from strain LSF9-1. Gene and genome analysis revealed that L. brevis LSF9-1 has multiple gad genes in the genome, such as gadB1 , gadB2 , gadC1 , and gadC2 , making it the potential strain for GABA production. Additionally, the genome analysis of P. acidilactici LSF1-1 consists of gadA , gadB , and gadC , which respond to controlling GABA production and export. Furthermore, strain LSF1-1 was considered safe, containing no virulence factors. Thus, Levilactobacillus brevis LSF9-1 and Pediococcus acidilactici LSF1-1 have the potential for GABA production and probiotic use in future studies.