Efficient Autoinducible Expression of Recombinant Proteins via the DegSU Quorum Sensing System in a Robust Bacillus subtilis

DegSU quorum sensing (QS) system enables autoinducible expression of recombinant proteins in Bacillus subtilis . However, insufficient promoter strength and a complex regulatory circuit limit its practical application. Here, the QS-responsive promoter PaprE was modified by core region mutation, upstream truncation, and addition of activating binding sites, yielding PE742 with a 118.3% increase in strength. A mathematical model was developed to accurately quantify the regulatory process from a comprehensive perspective. Guided by this model, the DegSU QS system was further optimized in a robust B. subtilis by knocking out competitive target genes sacB and amyE, operons pgs and srfA, introducing variants degUL113F and degQ36Hy, and increasing regulatory strength by 84.0%. A 52.5% increase in acetoin titer and a 65.9% increase in extracellular carboxypeptidase activity validated the industrial value of this study. Overall, this study addresses the limitations of the DegSU QS system in practical application and demonstrates its potential for high-level recombinant protein production.