IPTG can replace lactose in auto-induction media to enhance protein expression in batch-cultured Escherichia coli

Auto-induction media containing glucose, lactose, and glycerol are a simple and efficient approach for high-throughput protein expression in Escherichia coli with lac-derived expression systems. Its principle is based on inducer exclusion between glucose and lactose, preventing the induction by lactose before the depletion of glucose. Isopropyl-β-d-1-thiogalactopyranoside (IPTG)-at least in typically used millimolar concentrations-is thought to be unsuitable for this purpose since it can enter the cell by diffusion independently of inducer exclusion. In this study, using parallel batch cultivations in stirred-tank bioreactors on a milliliter scale, we show that the induction by micromolar concentrations of IPTG is prevented in the presence of glucose. With up to 40 μM IPTG, full induction and heterologous protein expression start only after the depletion of glucose. Thus, auto-induction is possible with either lactose or IPTG, and the expression greatly depends on the type and concentration of the inducer. The best expression of enhanced green fluorescent protein was achieved with 40 μM IPTG in stirred-tank bioreactors on a milliliter scale. The IPTG-based auto-induction was also reproduced in shaking flasks. Therefore, IPTG can be used in auto-induction media for protein expression in batch-cultured E. coli. Furthermore, we show that acetate or arabinose can have significant effects on the auto-induction mechanism.