Studies on gamma-aminobutyric acid production by immobilized Escherichia coli cells

E. coli cells with glutamate decarboxylase activity were immobilized by entrapment in calcium alginate gel lattices, followed by cross-linking with glutaric dialdehyde to increase mechanical strength. A large number of cells was immobilized in the gel, resulting in high enzyme activity. Optimum conditions for gamma-aminobutyric acid production were investigated. A comparative study of three reactor modes, i.e., batch, continuously stirred, and continuous column, found the optimal pH and temperature for -aminobutyric acid production to be 4.4 and 37 degrees C respectively. The batch process was run on a shaker at 120 r/min, the continuously stirred reaction (in a flask reactor) at 6 ml/h, and column production (in a special column reactor) at 12 ml/h. Conversion of the L-glutamate to gamma-aminobutyric acid was about 85-100% under these conditions. The immobilized cells could be regenerated by incubation in phosphopyridoxal coenzyme solution when enzyme activity and immobilized-cell throughput declined. The column-type process had some advantages over the others.