Generation of an Artificial Double Promoter for Protein Expression in Bacillus subtilis through a Promoter Trap System

Bacillus subtilis is an attractive host for production of recombinant proteins. Promoters and expression plasmid backbones have direct impacts on the efficiency of gene expression. To screen and isolate strong promoters, a promoter trap vector pShuttleF was developed in this study. Using the vector, approximately 1000 colonies containing likely promoters from Bacillus licheniformis genomic DNA were obtained. Amongst them, pShuttle-09 exhibited the highest β-Gal activities in both Escherichia coli and B. subtilis. The activity of pShuttle-09 in B. subtilis was eight times of that of the P43 promoter, a commonly used strong promoter for B. subtilis. A sequence analysis showed that pShuttle-09 contained P(luxS) and truncated luxS in-frame fused with the reporter gene as well as another fragment upstream of P(luxS) containing a putative promoter. This putative promoter was a hybrid promoter and its β-Gal activity was higher than P(luxS). Reconstructing the hybrid promoter from pShuttle-09 to P(lapS) further improved the β-Gal production by 60%. The usefulness of our promoter trap system is likely due to random shuffling and recombination of DNA fragments and adoption of a rapid and high-throughput screening. Thus, our data provide additional evidence to support the concept of using a promoter trap system to create new promoters.