Production of γ-Aminobutyrate (GABA) in Recombinant Corynebacterium glutamicum by Expression of Glutamate Decarboxylase Active at Neutral pH

γ-Aminobutyrate (GABA) is an important chemical by itself and can be further used for the production of monomer used for the synthesis of biodegradable polyamides. Until now, GABA production usingCorynebacterium glutamicum harboring glutamate decarboxylases (GADs) has been limited due to the discrepancy between optimal pH for GAD activity (pH 4.0) and cell growth (pH 7.0). In this study, we developed recombinant C. glutamicum strains expressing mutated GAD from Escherichia coli (EcGADmut) and GADs from Lactococcus lactis CICC20209 (LlGAD) and Lactobacillus senmaizukei (LsGAD), all of which showed enhanced pH stability and adaptability at a pH of approximately 7.0. In shake flask cultivations, the GABA productions of C. glutamicum H36EcGADmut, C. glutamicum H36LsGAD, and C. glutamicum H36LlGAD were examined at pH 5.0, 6.0, and 7.0, respectively. Finally, C. glutamicum H36EcGADmut (40.3 and 39.3 g L^-1), H36LlGAD (42.5 and 41.1 g L^-1), and H36LsGAD (41.6 and 40.2 g L^-1) produced improved GABA titers and yields in batch fermentation at pH 6.0 and pH 7.0, respectively, from 100 g L^-1glucose. The recombinant strains developed in this study could be used for the establishment of sustainable direct fermentative GABA production from renewable resources under mild culture conditions, thus increasing the availability of various GADs.