Broad-host-range application of the srfA promoter from Bacillus subtilis in Escherichia coli

The promoter of the srf operon (P_srfA) had been used to construct a cell-density-dependent expression system in B. subtilis in our previous work. The P_srfA and its derivative P_srfA12 showed good performance of heterologous protein expression in B. subtilis. In this work, using green fluorescent protein (GFP) and β-galactosidase (LacZ) as the reporter proteins, the host feasibility and expression characteristics of the P_srfA and P_srfA12 in E. coli were identified. The prominent green fluorescence shooted by laser scanning confocal microscope, fluorescence intensity measured by spectrophotometer and the distinct protein bands detected by SDS-PAGE demonstrated that the GFP could be largely expressed under the control of the P_srfA and P_srfA12 in the E. coli host strain of BL21 (DE3) and JM109 and the expression of GFP in strain BL21 (DE3) was much higher than that of in strain JM109. Meanwhile, the promoter P_srfA 12 was much stronger than P_srfA to the extent that the GFP controlled by P_srfA12 in strain BL21 (DE3) was leaked into the supernatant. And the fluorescence intensity detected in the supernatant of the recombinant strain BL21 (DE3) containing P_srfA12 was 10.25-fold higher than that of strain JM109 containing P_srfA. Moreover, the LacZ could also be produced by P_srfA and P_srfA12 in strain BL21 (DE3) and JM109 and the strain JM109 showed better performance than BL21 (DE3) in expressing LacZ. The LacZ activity controlled by P_srfA and P_srfA12 in JM109 were separately 2.47-fold and 2.36-fold higher than that of in strain BL21 (DE3). This work will broaden the applied range of the P_srfA and enrich the efficient toolbar for cross-species gene expression or module construction in E. coli and B. subtilis.