An Engineered Inducible Promoter System with over 10 000-Fold Dynamic Range.

is the leading model Gram-positive bacterium, and a widely used chassis for industrial protein production. However, research is limited by a lack of inducible promoter systems with low leakiness and high dynamic range. Here, we engineer an inducible promoter system based on the T7 RNA Polymerase (T7 RNAP), the lactose repressor LacI, and the chimeric promoter P, integrated as a single copy in the genome. In the absence of IPTG, LacI strongly represses T7 RNAP and P and minimizes leakiness. Addition of IPTG derepresses P and simultaneously induces expression of T7RNAP, which results in very high output expression. Using green fluorescent and β-galactosidase reporter proteins, we estimate that this LacI-T7 system can regulate expression with a dynamic range of over 10 000, by far the largest reported for an inducible promoter system. Furthermore, LacI-T7 responds to similar IPTG concentrations and with similar kinetics as the widely used P IPTG-inducible system, which we show has a dynamic range of at most 300 in a similar genetic context. Due to its superior performance, our LacI-T7 system should have broad applications in fundamental biology studies and biotechnology.