Isolation and Optimal Fermentation Condition of the Bacillus subtilis Subsp. natto Strain WTC016 for Nattokinase Production

Nattokinase is a serine protease in the subtilisin family which is produced by Bacillus subtilis subsp. natto and exhibits vigorous fibrinolytic activity that has been suggested to be able to prevent and treat thromboembolic diseases. In this study, WTC016, a spore-forming and rod-shaped bacterium with fibrinolytic activity was successfully isolated from soil, which was identified as Bacillus subtilis subsp. natto based on morphological and physiological tests, and phylogenetic analysis of 16S rRNA and gyrA. According to the growth curve of WTC016, the nattokinase production reached the highest amount in the stationary phase. To optimize the liquid fermentation condition for nattokinase yield of WTC016, further optimal tests of four factors, including the temperature, pH, inoculum size, and loading volume, followed by orthogonal test of all these factors, was performed. The optimal fermentation conditions were determined as 30 degrees C, 7.0 pH, 2% inoculum size, and 60 mL of loading volume in 250 mL conical flask, which indicates the highest nattokinase production of 3284 +/- 58 IU/mL while fermented for 26 h. This work laid the foundation for producing nattokinase using Bacillus subtilis subsp. natto WTC016.