Enhanced β-galactosidase production by high cell-density culture of recombinantBacillus subtiliswith glucose concentration control

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Abstract
Cell concentration, recombinant protein (β‐galactosidase) level, and the specific enzyme expression level were increased from 19 to 184 g/L, 18.3 to 129 U/mL, and 3.2 to 5.7 U/mg protein, respectively, in fed‐batch culture of recombinant Bacillus subtilis when glucose concentration was controlled at 1 g/L as compared with those of conventional fed‐batch culture. Glucose concentration of the culture broth was monitored by an automatic on‐line glucose analyzer and controlled with a moving identification combined with optimal control (MICOC) strategy. When glucose concentrations were controlled at 10, 1, and 0.2 g/L, accumulated propionic acid concentrations and specific enzyme activities were 18.5, 4.4, and 0.6 g/L and 2.9, 5.7, and 7.1 U/mg protein, respectively. The addition of various concentrations of sodium propionate to the growth medium in batch cultures resulted in a drastic decrease in the growth rate with respect to propionate concentration. The propionic acid was shown to be responsible for cell growth inhibition and enzyme activity reduction in fed‐batch culture. © 1992 John Wiley & Sons, Inc.