On-line detection of acetate formation in Escherichia coli cultures using dissolved oxygen responses to feed transients

Recombinant protein production in Escherichia coli can be significantly red uced by acetate accumulation. It is demonstrated that acetate production ca n be detected on-line with a standard dissolved oxygen sensor by superimpos ing short pulses to the substrate feed rate. Assuming that acetate formatio n is linked to a respiratory limitation, a model for dissolved oxygen respo nses to transients in substrate feed rate is derived. The model predicts a clear change in the character of the transient response when acetate format ion starts. The predicted effect was verified in fed-batch cultivations of E. coli TOPP1 and E. coli BL21(DE3), both before and after induction of rec ombinant protein production. It was also observed that the critical specifi c glucose uptake rate, at which acetate formation starts, was significantly decreased after induction. On-line detection of acetate formation with a s tandard sensor opens up new possibilities for feedback control of substrate feeding. (C) 1999 John Wiley & Sons, Inc.