A novel γ-aminobutyric acid biosynthetic pathway in Lentilactobacillus curieae CCTCC M 2011381T

Gamma-aminobutyric acid (GABA) is an important neurotransmitter for mammals, thus biosynthesized or bio-transformed GABA is an important compound for functional foods. In this study, unique biosynthetic pathways of GABA in a novel lactic acid bacteria (LAB) strain, Lentilactobacillus curieae CCTCC M 2011381T, was discovered. L-glutamate decarboxylase (GAD) which generally catalyzes L-glutamate decarboxylation to form GABA in bacteria, is absent in this strain. Alternatively, transcriptional analysis revealed that L-glutamate played as an amino donor for the step through which succinic semialdehyde (SSA) was converted to GABA catalyzed by GABA transaminase (GABA-T). Then, the deletion and complementation of the GABA-T gene confirmed that GABA-T was the key enzyme responsible for GABA accumulation from SSA. According to residual GABA titer could be detected after the deletion of the GABA-T gene, other decarboxylases among the genome were analyzed by RT-PCR. 5-Oxopent-3-ene-1,2,5-tricarboxylate decarboxylase (HpaG) was verified possessing weaker catalytic capability for the decarboxylation of L-glutamate based on the hetero-expression of the enzyme in E. coli. Thus, GABA is produced mainly through the transamination reaction on SSA catalyzed by GABA-T and L-glutamate as the amino donor, and slightly from the decarboxylation of L-glutamate catalyzed by HpaG in L. curieae, which are distinct pathways in LAB.