IMPROVEMENT OF HETEROLOGOUS PROTEIN PRODUCTIVITY BY CONTROLLING POSTINDUCTION SPECIFIC GROWTH-RATE IN RECOMBINANT ESCHERICHIA-COLI UNDER CONTROL OF THE P-L PROMOTER

To develop the optimal operational strategy for the PL promoter of int erferon (IFN)-gamma-producing Escherichia coli, some rational medium f eeding methods, carried out just after temperature induction to contro l the postinduction specific growth rate (mu(i)), were designed. Using experimental data from various batch cultures, we correlated mu(i) wi th specific IFN-gamma production rate (q(pi)) to find out how mu(i) ju st after induction affected q(pi). It was revealed that sustaining mu( i) above a certain value after induction was the key factor for high-l evel production of IFN-gamma. Stepwise and constant-rate medium feedin g, 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) aft er temperature induction. These methods led to the overcoming of harsh conditions after temperature induction and the improvement of IFN-gam ma productivity. Finally, by both a high-cell-density culture using an exponential fed-batch culture for cell growth and constant-rate mediu m feeding after temperature induction for IFN-gamma production, we acc omplished an increase in IFN-gamma production by 23-fold, 7.43 g/L, as compared with that of batch culture.