High-Yield Bacillus subtilis Protease Production by Solid-State Fermentation

Abstract

A Bacillus subtilis isolate was shown to be able to produce extracellular protease in solid-state fermentations (SSF) using soy cake as culture medium. A significant effect of inoculum concentration and physiological age on protease production was observed. Maximum activities were obtained for inoc-ula consisting of exponentially growing cells at inoculum concentrations in the range of 0.7–2.0 mg g−1. A comparative study on the influence of cultivation temperature and initial medium pH on protease production in SSF and in submerged fermentation (SF) revealed that in SSF a broader pH range (5–10), but the same optimum temperature (37°C), is obtained when compared to SF. A kinetic study showed that enzyme production is associated with bacterial growth and that enzyme inactivation begins before biomass reaches a maximum level for both SF and SSF. Maximum protease activity and productivity were 960 U g−1 and 15.4 U g−1 h−1 for SSF, and 12 U mL−1 and 1.3 U mL−1 h−1 for SF. When SSF protease activity was expressed by volume of enzyme extract, the enzyme level was 10-fold higher and the enzyme productivity 45% higher than in SF. These results indicate that this bacterial strain shows a high biotechnological potential for protease production in solid-state fermentation.