Isolation and Optimal Fermentation Conditions of Bacillus licheniformis SFD-Y5 for a New Douchi Fibrinolytic Enzyme Producer

Cardiovascular disease (CVD) has become the leading cause of death, and it is critical to develop new functional foods to prevent intravascular thrombosis, the key cause of CVD. Fermented soy-based food is a good choice because of its native fibrinolytic enzyme (FE) activity. In this study, a strain that can produce a new type of fibrinolytic enzyme was selected from Chinese Douchi and identified as Bacillus licheniformis SFD-Y5 by molecular biology experiments and physiological and biochemical experiments. Single factor experiments combined with statistical experiments, including Plackett–Burman experiment, steepest ascent experiment and RSM (Box–Behnken design), were used to optimize the fermentation of FE by B. licheniformis SFD-Y5. The final FE activity was 2434.45 ± 28.49 IU/mL under optimal conditions, which is the highest FE activity produced by wild B. licheniformis so far. Further studies showed that Y5 FE is a serine metalloproteinase with good stability at alkaline pHs (pH 8.0–11.0). The results of our study could lay a foundation for the future production, molecular modification and further application in functional foods of Y5 FE.