Synergism of regulatory elements in σ(B)- and σ(A)-dependent promoters enhances recombinant protein expression in Bacillus subtilis.

Strong promoter is an essential factor for production of recombinant protein in various expression systems including Bacillus subtilis. In this study, we described a strategy to improve the expression efficiency using synthetic double promoter. Assembly of the conserved elements from σ(B)- and σ(A)-dependent promoters constitutively improved the yield of recombinant protein approximately 2-3-fold in both exponential and stationary growth phase. The synergistic effect in the double promoter was observed only when σ(B)-promoter was located upstream to σ(A)-promoter but independent to its orientation. A conserved element in either -10 or -35 box of σ(B)-promoter is sufficient to promote the synergism. Hence, this simple strategy of promoter engineering could be an effective way to generate a pool of strong constitutive promoters applicable for heterologous protein expression in B. subtilis in the future.