Bacillus subtilis is an aerobic, Gram-positive soil bacterium. It secretes numerous enzymes to degrade a variety of substrates, enabling the bacterium to survive in a continuously changing environment. B. subtilis expression systems with good genetic stability are available for various purposes. It has excellent protein secretion ability and no strong codon preference, making it important host for the production of heterologous proteins. Moreover, the CRISPR/cas9 tool has been widely used in the genetic engineering of B. subtilis for production of industrial chemicals or enzymes, medicine, and biomaterials. B. subtilis is generally recognized as safe (GRAS).