Mass production of thermostable D-hydantoinase by batch culture of recombinant Escherichia coli with a constitutive expression system

Abstract

D-Hydantoinase is an industrial enzyme widely used for the synthesis of optically active D-amino acids. A gene encoding thermostable D-hydantoinase of Bacillus stearothermophilus SD-1 has previously been cloned and constitutively expressed by its native promoter in Escherichia coli XL1-Blue (Lee et al., 1996b). In this work, we attempted mass production of the D-hydantoinase by batch culture of the recombinant E. coli using glycerol as a carbon source. The plasmid content in cells increased in proportion to the culture temperature, which resulted in a two- or three-fold increase of the specific D-hydantoinase activity at 37 degrees C compared with that at 30 degrees C. The plasmid was stably maintained over 80 generations. When glycerol was initially added to a concentration of 100 g/L, the final biomass concentration reached about 50 g-dry cell weight/L in a 50 L-scale fermentation, resulting in the specific enzyme production of 3.8 x 10(4) unit/g-dry cell weight in a soluble form. Glycerol-using batch cultivation of recombinant E. coli was found to be a cost-effective process for the mass production of industrially useful D-hydantoinase. (C) 1997 John Wiley & Sons, Inc.