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Background  We recently constructed a  Bacillus subtilis  strain (CCTCC M 2016536) from which we had deleted the  srfC ,  spoIIAC ,  nprE ,  aprE  and  amyE  genes. This strain is capable of robust recombinant protein production and amenable to high-cell-density fermentation. Because the promoter is among the factors that influence the production of target proteins, optimization of the initial promoter, P amyQ  from  Bacillus amyloliquefaciens , should improve protein expression using this strain. This study was undertaken to develop a new, high-level expression system in  B. subtilis  CCTCC M 2016536.    Results  Using the enzyme β-cyclodextrin glycosyltransferase (β-CGTase) as a reporter protein and  B. subtilis  CCTCC M 2016536 as the host, nine plasmids equipped with single promoters were screened using shake-flask cultivation. The plasmid containing the P amyQ′  promoter produced the greatest extracellular β-CGTase activity; 24.1 U/mL. Subsequently, six plasmids equipped with dual promoters were constructed and evaluated using this same method. The plasmid containing the dual promoter P HpaII –P amyQ′  produced the highest extracellular β-CGTase activity (30.5 U/mL) and was relatively glucose repressed. The dual promoter P HpaII –P amyQ′  also mediated substantial extracellular pullulanase (90.7 U/mL) and α-CGTase expression (9.5 U/mL) during shake-flask cultivation, demonstrating the general applicability of this system. Finally, the production of β-CGTase using the dual-promoter P HpaII –P amyQ′  system was investigated in a 3-L fermenter. Extracellular expression of β-CGTase reached 571.2 U/mL (2.5 mg/mL), demonstrating the potential of this system for use in industrial applications.    Conclusions  The dual-promoter P HpaII –P amyQ′  system was found to support superior expression of extracellular proteins in  B. subtilis  CCTCC M 2016536. This system appears generally applicable and is amenable to scale-up.    Electronic supplementary material  The online version of this article (doi:10.1186/s12934-017-0649-1) contains supplementary material, which is available to authorized users.

High-level extracellular protein production in Bacillus subtilis using an optimized dual-promoter expression system