Whole-cell display of Pyrococcus horikoshii glutamate decarboxylase in Escherichia coli for high-titer extracellular gamma-aminobutyric acid production.

We investigated the effect of cell-surface display of glutamate decarboxylase (GadB) on gamma-aminobutyric acid (GABA) production in recombinant Escherichia coli. We integrated GadB from the hyperthermophilic, anaerobic archaeon Pyrococcus horikoshii to the C-terminus of the E. coli outer membrane protein C (OmpC). After 12 hr of culturing GadB-displaying cells, the GABA concentration in the extracellular medium increased to 3.2 g/l, which is eight times that obtained with cells expressing GadB in the cytosol. To further enhance GABA production, we increased the temperatures of the culture. At 60°C, the obtained GABA concentration was 4.62 g/l after 12 hr of culture, and 5.35 g/l after 24 hr, which corresponds to a yield of 87.7%.