Isolation and genetic analysis of an Enterococcus gallinarum strain with high GABA-producing capacity from the murine intestine

Some intestinal bacteria possess the glutamate decarboxylase ( gad ) gene and can produce γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter in mammals, from glutamate. The physiological role of gut-microbiota-derived GABA has attracted attention because of the relationships identified between gut microbiota and psychiatric and neurological disorders. We screened for GABA-producing or GABA-consuming bacteria in the murine intestine using selective media targeting two groups of bacteria that were reduced or increased in children with autism spectrum disorder: Lactobacillales and Clostridiales. As a result, an Enterococcus gallinarum strain belonging to Lactobacillales was identified as a high GABA producer. The isolated strain possesses the gad cluster and produced larger amounts of GABA from glutamate than the Levilactobacillus brevis strain, a well-known GABA producer. This study identified a novel gut-resident bacterium with a high GABA production capacity as a potential source of intestinal GABA. • An Enterococcus gallinarum strain was isolated from the murine intestine. • This strain produced high levels of GABA from glutamate. • Whole-genome sequencing revealed the presence of a gad gene cluster. • The cluster contained gad C, gad , and a gene encoding helix-turn-helix protein.