Establishment of a low‐dosage‐IPTG inducible expression system construction method in Escherichia coli

The lac operon is a delicate inducible gene expression element in bacteria. To efficiently induce gene expression, a sufficient dosage of an inducer, usually that of 500–1000 µM isopropyl β‐D‐1‐thiogalactopyranoside (IPTG), is required to keep repressor LacI from its binding sites, which is a heavy cost burden in low‐value‐added products. So we propose a strategy to reduce the required dosage of IPTG by restricting LacI expression. To test this strategy, we employed a reconstructed IPTG inducible expression system based on lac operon, Promoter( lacO )‐target gene‐P tac L‐ lacI , where a modified promoter, P tac , with a random synthetic library (P tac L) to instead of P lacI to optimize LacI expression in Escherichia coli . Finally, the P tac L mutant, P tac L4, which could maintain the same repression effect as the original P lacI while reducing the required dosage of IPTG from 500 to 20 µM, was selected. This method is simple and efficient and can be of a good reference point for attempts to reduce inducer concentration in the IPTG or similar inducible expression systems.