Efficient production of biosurfactant surfactin by a newly isolated Bacillus subtilis (sp.) 50499 strain from oil-contaminated soil

Abstract

Biosurfactant surfactin has a high market value and broad application prospects in the food industry and various industrial fields. However, its production efficiency limits its suitability for real applications. In this study, a new Bacillus subtilis (sp.) 50499 strain was isolated from crude oil-contaminated soil and used to efficiently produce surfactin. The initial surfactin titer was 2.25 g/L after three days of fermentation. Adding 2 g/L of L-Leu significantly improved the titer to over 5.5 g/L after optimizing the culture medium at 37 °C. However, adding D-Leu had the opposite effect on surfactin production, and the surfactin titer dropped to below 0.2 g/L. Furthermore, the product of this strain was analyzed to confirm the identity of surfactin. The surfactin obtained in the present study reduced the surface tension of water to 28.6 mN/m at a critical micelle concentration of 20 mg/L. The emulsification index against n-hexane, corn, and crude oil was as high as over 90%. Hence, the present study provides a newly over-producing strain for surfactin production.