Activity dynamics and regulation mechanism of extracellular proteases in <i>Bacillus velezensis</i> SW5

<i>Bacillus velezensis</i> is capable of producing and secreting a rich variety of proteases, making it an excellent catalyst for food fermentation and bioremediation, as well as a promising source of proteases with industrial application potential. However, our knowledge of the activity and regulation mechanism of extracellular proteases in <i>B. velezensis</i> during growth remains limited. In our study, we investigated the growth dynamics, extracellular protease activity, and transcriptional profiles of <i>B. velezensis</i> strain SW5 over the course of the incubation period. The growth dynamics analysis showed that the cell density of SW5 increased exponentially until 10 h post-incubation, then declined or remained stable afterward. However, the extracellular protease activity followed the opposite trend: it remained low during exponential growth but significantly increased during the stationary phase, peaking at 54 h. Transcriptomic analyses showed that key extracellular proteases, such as AprE (subtilisin), exhibited maximal expression levels at 54 h and contributed primarily to extracellular protease activity. The transcriptomic data also identified key regulatory systems of extracellular proteases, including DegQ, DegU, ComQXPA quorum-sensing system, and negative regulators (e.g., AbrB, Hpr/ScoC, and CodY), which collectively regulate protease gene expression in <i>B. velezensis</i>. Overall, our study offers comprehensive insights into the activity dynamics and potential regulatory mechanisms of extracellular proteases in <i>B. velezensis</i>, providing a theoretical foundation for the industrial application of <i>B. velezensis</i> and its proteases.IMPORTANCE<i>Bacillus velezensis</i> holds significant economic relevance for fermentation products due to its excellent biosafety profile and strong proteolytic capabilities. Therefore, understanding the dynamics of extracellular protease activity and their corresponding regulatory mechanisms in <i>B. velezensis</i> is of great significance. In our study, we monitored the extracellular protease activity of strain SW5 and highlighted changes in the transcription levels of extracellular protease genes and their regulators throughout the incubation period. Notably, the transcriptomic data suggested that the extracellular protease activity was likely regulated by a complex network involving the DegS-DegU two-component system, the ComQXPA quorum-sensing system, DegQ, and negative regulators. Our results also revealed distinct expression patterns among extracellular protease genes and their regulators at different growth stages, highlighting the growth stage-specific regulation mode of extracellular proteases. These findings offer valuable insights into the proteolytic characteristics in <i>B. velezensis,</i> as well as the industrial application potential of <i>B. velezensis</i>.