In order to improve the yield of nattokinase and promote its industrial production and application, Bacillus subtilis was isolated from fresh natto from five different producing areas, and the strain with larger ratio of hydrolysis circle to colony was selected through preliminary screening of colony morphology and re-screening of casein plate, and the nattokinase activity in its fermentation broth was measured, and a strain X3 with relatively high enzyme activity was selected. X3 strain was identified as Bacillus subtilis by systematic 16S rDN...
