Recombinant Protein Production in High Cell Density Cultures of Escherichia coli with Galactose as a Gratuitous Inducer

A new expression system was developed by introducing two major modifications into the genome of Escherichia coli : a deletion in the gal operon (Δ galEKT ) to allow the use of the inexpensive compound galactose as a gratuitous inducer and the introduction of the gal P 2 promoter driving the expression of the T7 RNA polymerase. The novel JRR10 strain containing these two features gives high‐level expression of a reporter gene cloned under the T7 ϕ10 promoter in high cell density cultures. The cost of the induction of this novel system is more than 30 times lower than that of the IPTG‐induced system of the widely used BL21 strain.