Systematic Screening of Optimal Signal Peptides for Secretory Production of Heterologous Proteins in Bacillus subtilis.

Bacillus subtilis is widely used for large-scale industrial production of heterologous proteins. Because of its high intrinsic secretory capacity, it can efficiently secrete proteins into the culture supernatant via the general Sec-type secretion pathway. In this study, the α-amylase AmyS was used as a reporter to construct a library encompassing 173 Sec-type signal peptides (SPs) from B. subtilis using a fast, sequence-independent method. The resulting library DNA which harbored different signal peptides in the expression vector was used to transform B. subtilis directly at high efficiency, and 15 SPs which produced a significantly increased yield of AmyS were identified using a starch-iodine-based high-throughput assay. Furthermore, the correlation between the sequences of the best-performing signal peptides and their secretion efficiency was analyzed, which revealed several common properties of these SPs. Finally, high-cell-density fermentation of the α-amylase-producing strain with the best-performing signal peptide yielded a maximum of 5086 U/mL amylase at 66 h with a high productivity of 77.1 U/mL·h.