Zymogram Analysis and Identification of the Extracellular Proteases from Bacillus velezensis SW5

Abstract Bacillus velezensis is regarded as a potential starter culture for food, due to its biological safety and efficient protein hydrolysis ability. To clarify the diversity of extracellular proteases produced by B. velezensis SW5 isolated from fish sauce, substrate immersing zymography and peptide analysis based on MS were used. A total of 12 proteases were identified in the extracellular fermentation broth of B. velezensis SW5, and it was found that the strain produces some unknown proteases. Among them, only subtilisin E, bacillopeptidase F, and bacillolysin had signal peptides. Subtilisin E comprised the majority of the protease activity of B. velezensis SW5. Both subtilisin E and bacillopeptidase F are serine proteases from S8A peptide subfamily, while bacillolysin is a metalloproteinase in the peptidase M4 family. These proteases formed multiple substrate hydrolysis bands during non-denaturing electrophoresis, indicating that they exist outside the cell in various mature forms. Nine signal peptide-free proteases, from a number of different protease families, such as S8A, G2, M16B, U32, C15, M20B, and M23B, were also identified in the cell-free supernatant of the strain. The composition of extracellular proteases in B. velezensis SW5 is complex, and the catalytic types of these proteases are diverse.