Improvement of heterologous protein productivity by controlling postinduction specific growth rate in recombinant Escherichia coli under control of the PL promoter.

To develop the optimal operational strategy for the PL promoter of interferon (IFN)-gamma-producing Escherichia coli, some rational medium feeding methods, carried out just after temperature induction to control the postinduction specific growth rate (mu i), were designed. Using experimental data from various batch cultures, we correlated mu i with specific IFN-gamma production rate (qpi) to find out how mu i just after induction affected qpi. It was revealed that sustaining mu i above a certain value after induction was the key factor for high-level production of IFN-gamma. Stepwise and constant-rate medium feeding, in which the temperature induction was done simultaneously, at the late-exponential growth phase of batch culture resulted in a dramatic extension of the production period as a result of sustaining mu i after temperature induction. These methods led to the overcoming of harsh conditions after temperature induction and the improvement of IFN-gamma productivity. Finally, by both a high-cell-density culture using an exponential fed-batch culture for cell growth and constant-rate medium feeding after temperature induction for IFN-gamma production, we accomplished an increase in IFN-gamma production by 23-fold, 7.43 g/L, as compared with that of batch culture.