Efficient production of extracellular alkaline protease in Bacillus amyloliquefaciens by host strain construction

Bacillus amyloliquefaciens is an important industrial microorganism, which can be applied as a protein expression host. However, the extracellular protein expression ability of B. amyloliquefaciens is still low. Hence, it is necessary to develop a B. amyloliquefaciens host with a high extracellular protein expression capacity. In this study, B. amyloliquefaciens HZ-12 was the original strain, then seven important extracellular protease genes (epr, nprE, aprE-a, mpr, pbpF, vpr, ykct1), one important intracellular protease gene (aprX) and two redundant proteins genes (htrB, hag) were deleted in HZ-12, resulting in B. amyloliquefaciens BAX-10. In order to evaluate the extracellular protein expression ability of BAX-10, the alkaline protease gene aprE from Bacillus subtilis D7 was expressed in BAX-10. After fermentation, the alkaline protease activity of BAX-10/aprE reached 666.82 U/mL, which was 57% higher than that of the control strain HZ/aprE. Moreover, the deletion of the ten genes had no negative effect on the growth of B. amyloliquefaciens. In summary, B. amyloliquefaciens BAX-10 could be used as a potential platform host for expression of target extracellular proteins.