Research progress on Bacillus subtilis expression systems and effects of different promoters on expression efficiency

This review systematically summarizes the features of Bacillus subtilis expression systems, the regulatory effects of various promoters on heterologous expression efficiency, and rational modification strategies of promoter core regions. B. subtilis WB600 or WB800 are the preferred hosts for autonomous plasmid-based expression systems due to their multiple protease deletions, which reduce recombinant protein degradation. In contrast, wild-type strains are more suitable for chromosomal integration systems because of native genomic background and physiological characteristics, which are advantageous for long-term stable expression. Constitutive promoters are suitable for stable and large-scale industrial enzyme production, while inducible promoters realize accurate and tunable control of gene expression. Dual promoters can effectively enhance transcription and protein yield, but are not universally superior to single promoters, and the final expression efficiency mainly depends on the downstream promoter adjacent to the target gene. Core region modification, such as optimizing the consensus sequences of the -35 and - 10 regions and adjusting the spacer length, can significantly improve promoter strength and consequently protein expression. The coordinated optimization of host-promoter-critical elements is critical to achieve highly efficient expression of target products. This review provides a theoretical basis for the further development and application of B. subtilis expression systems, offering valuable references for the rational development of high-efficiency promoter engineering strategies and heterologous gene expression optimization.