Construction and optimization of engineered Bacillus subtilis for surfactin production / 生物工程学报

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.

Exploring novel drug targets in fatty acid pathway of Plasmodium falciparum.

The malarial parasite Plasmodium falciparum infects humans and proliferates rapidly inside the host before its detection. The proliferation step requires a large amount of lipids for membrane synthesis. Thus fatty acid biosynthesis occurring in the apicoplast plays an important role in causing cerebral malaria. In this study, we explored and analyzed these pathways using stoichiometric matrix, elementary flux modes and robustness analysis. Based on the above analysis, the robustness of this pathway diminished as the result of virtual enzyme knock out indicating four key enzymes, 3-oxoacyl-ACP synthase, 3-oxoacyl-ACP synthase, 3-oxoacyl-ACP synthase and Glycerol-3-phosphate o-acyl transferase. Among the four, the first three are existing drug targets. Subsequently, we also found that a combinatorial double knock out of these enzymes predicts further reduction in overall pathway enzyme activity. Thus, we propose multi drug targeting as a better way to treat brain malaria.