Process strategies to improve heterologous protein production in Escherichia coli under lactose or IPTG induction

Cells of Escherichia coli BL21 bearing the chicken muscle Troponin C (TnC) gene under the control of the lacUV5 promoter were induced under different cultivation conditions and the consequences on growth and cell protein cont ent were investigated. The type of inducer molecule (lactose or IPTG), the average carbon source concentration (0.0-10.6 g l(-1)), the specific growth rate at the beginning of induction (0.20-0.54 h(-1)), and the cell concent ration at the beginning of induction (3.2-36.5 g l(-1)) were varied. The hi ghest value for the intracelIular level of the target protein (TnC(X)), 110 mg per gram dry cell weight (DCW), was achieved when isopropyl-beta-D-thio galactoside (IPTG) was the inducer. Under lactose induction, a value of 96 mg per gram DCW was attained. However, the high metabolic load imposed by I PTG, when compared with lactose induction, as assessed by the cell protein content and stability, indicates that lactose is probably the most appropri ate inducer for the synthesis of this heterologous protein. (C) 2000 Elsevi er Science Ltd. All rights reserved.