Construction and optimization of engineered Bacillus subtilis for surfactin production

Surfactin has great potential applications in enhancing oil recovery, agriculture, pharmaceuticals, foods and beverages, and cosmetics due to its extraordinary surface activity, biodegradability, anti-bacterial activity and biocompatibility. Enhancing surfactin production by engineering surfactin-producer and optimizing culture conditions is the key of its industrial production and subsequent applications. In this study, the effect of fatty acid synthesis pathway on surfactin synthesis was investigated, and Bacillus subtilis THBS-2 and THBS-8 with high surfactin titer were constructed by overexpressing key genes involved in the fatty acid synthesis pathway. To optimize culture condition, the amount and adding time of isopropyl-beta-D-thiogalactopyranoside (IPTG) and amino acids were studied, and a two-stage culture method was obtained: IPTG (final concentration: 1.25 mmol/L) and leucine (final concentration: 5 g/L) were added at 3 h, leucine (final concentration 5 g/L) and condensed culture medium (5 mL) were added at 24 h. Applying this strategy, the surfactin titer of B. subtilis THBS-2 reached to 24 g/L in shake flask at 48 h and up to 34 g/L after 68 h fermentation in a 30-L fermentor. The results provide basis for large-scale production and broad application of surfactin.