Robust production of gamma-amino butyric acid using recombinant Corynebacterium glutamicum expressing glutamate decarboxylase from Escherichia coli.

Gamma-amino butyric acid (GABA) is a component of pharmaceuticals, functional foods, and the biodegradable plastic polyamide 4. Here, we report a simple and robust system to produce GABA from glucose using the recombinant Corynebacterium glutamicum strain GAD, which expresses GadB, a glutamate decarboxylase encoded by the gadB gene of Escherichia coli W3110. As confirmed by HPLC analysis, GABA fermentation by C. glutamicum GAD cultured at 30°C in GABA Production 1 (GP1) medium containing 50 g/L glucose without the addition of glutamate yielded 8.07 ± 1.53 g/L extracellular GABA after 96 h. Addition of 0.1mM pyridoxal 5'-phosphate (PLP) was found to enhance the production of GABA, whereas Tween 40 was unnecessary for GABA fermentation. Using the optimized GABA Production 2 (GP2) medium, which contained 50 g/L glucose and 0.1mM PLP, fermentation was performed in a flask at 30°C with 10% (v/v) seed culture of C. glutamicum GAD. GABA was produced in the culture supernatant with a yield of 12.37 ± 0.88 g/L after 72 h with a space-time yield of 0.172 g/L/h, which is the highest yield obtained to date for GABA from fermentation with glucose as a main carbon source.

Glutamate production from ß-glucan using endoglucanase-secreting Corynebacterium glutamicum.

We demonstrate glutamate production from ß-glucan using endoglucanase (EG)-expressing Corynebacterium glutamicum. The signal sequence torA derived from Escherichia coli K12, which belongs to the Tat pathway, was suitable for secreting EG of Clostridium thermocellum using C. glutamicum as a host. Using the torA signal sequence, endoglucanase from Clostridium cellulovorans 743B was successfully expressed, and the secreted EG produced 123 mg of reducing sugar from 5 g of ß-glucan at 30 °C for 72 h, which is the optimal condition for C. glutamicum growth. Subsequently, glutamate fermentation from ß-glucan was carried out with the addition of Aspergillus aculeatus ß-glucosidase produced by recombinant Aspergillus oryzae. Using EG-secreting C. glutamicum, 178 mg/l of glutamate was produced from 15 g of ß-glucan. This is the first report of glutamate fermentation from ß-glucan using endoglucanase-secreting C. glutamicum.

Direct production of cadaverine from soluble starch using Corynebacterium glutamicum coexpressing alpha-amylase and lysine decarboxylase.

Here, we demonstrated the one-step production of cadaverine from starch using a Corynebacterium glutamicum strain coexpressing Streptococcus bovis 148 alpha-amylase (AmyA) and Escherichia coli K-12 lysine decarboxylase (CadA). We constructed the E. coli-C. glutamicum shuttle vector, which produces CadA under the control of the high constitutive expression (HCE) promoter, and transformed this vector into C. glutamicum CSS secreting AmyA. The engineered C. glutamicum expressed both CadA and AmyA, which retained their activity. We performed cadaverine fermentation using 50 g/l soluble starch as the sole carbon source without pyridoxal-5'-phosphate, which is the coenzyme for CadA. C. glutamicum coexpressing AmyA and CadA successfully produced cadaverine from soluble starch and the yield of cadaverine was 23.4 mM after 21 h. CadA expression levels under the control of the HCE promoter were assumed to be sufficient to convert L-lysine to cadaverine, as there was no accumulation of L-lysine in the culture medium during fermentation. Thus, we demonstrated that C. glutamicum has great potential to produce cadaverine from biomass resources.