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

摘要

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.