Development of a synthetic cumate-inducible gene expression system for Bacillus

A novel inducible gene expression system using p-isopropyl benzoate (cumate) as an inducer was developed for the industrial production hosts, Bacillus subtilis and Bacillus megaterium. Cumate is non-toxic to the host, inexpensive, and carbon source-independent inducer which provides an economical option for large-scale production of valuable proteins and chemicals from Bacillus strains. The synthetic cumate-inducible system was constructed by combining the strong constitutive Bacillus promoter P_veg with regulatory elements of the Pseudomonas putida, CymR repressor, and its operator sequence CuO. The designed expression cassette containing a sfGFP reporter under the cumate-inducible promoter was assembled into a Bacillus-E. coli shuttle and gene expression investigated in the two Bacillus strains. Characterization of gene expression levels, expression kinetics, and dose-response to cumate inducer concentration confirmed high-level, but tightly controlled GFP reporter expression in tunable, cumate concentration-dependent manner. Unexpectedly, this expression system works equally well for Escherichia coli, resulting in a platform that can be used both in gram-positive and gram-negative expression host. Its tight regulation and controllable expression makes this system useful for metabolic engineering, synthetic biology studies as well industrial protein production.