Improved production of Bacillus subtilis cholesterol oxidase by optimization of process parameters using response surface methodology

BACKGROUND: Cholesterol oxidase has numerous biomedical and industrial applications. In the current study, a new bacterial strain was isolated from sewage and was selected for its high potency for cholesterol degradation (%) and production of high cholesterol oxidase activity (U/OD(600)). RESULTS: Based on the sequence of 16S rRNA gene, the bacterium was identified as Bacillus subtilis. The fermentation conditions affecting cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD(600)) of B. subtilis were optimized through fractional factorial design (FFD) and response surface methodology (RSM). According to this sequential optimization approach, 80.152% cholesterol degradation was achieved by setting the concentrations of cholesterol, inoculum size, and magnesium sulphate at 0.05 g/l, 6%, and 0.05 g/l, respectively. Moreover, 85.461 U of cholesterol oxidase/OD(600) were attained by adjusting the fermentation conditions at initial pH, 6; volume of the fermentation medium, 15 ml/flask; and concentration of cholesterol, 0.05 g/l. The optimization process improved cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD(600)) by 139% and 154%, respectively. No cholesterol was detected in the spectroscopic analysis of the optimized fermented medium via gas chromatography-mass spectroscopy (GC–MS). CONCLUSION: The current study provides principal information for the development of efficient production of cholesterol oxidase by B. subtilis that could be used in various applications.