Find in Library

Surfactin is widely used in the petroleum extraction, cosmetics, biopharmaceuticals and agriculture industries. It possesses antibacterial and antiviral activities and can reduce interfacial tension. <i>Bacillus</i> are commonly used as production chassis, but wild-type <i>Bacillus subtilis</i> 168 cannot synthesise surfactin. In this study, the phosphopantetheinyl transferase (PPTase) gene <i>sfp</i>* (with a T base removed) was overexpressed and enzyme activity was restored, enabling <i>B. subtilis</i> 168 to synthesise surfactin with a yield of 747.5 ± 6.5 mg/L. Knocking out <i>ppsD</i> and <i>yvkC</i> did not enhance surfactin synthesis. Overexpression of predicted surfactin transporter gene <i>yfiS</i> increased its titre to 1060.7 ± 89.4 mg/L, while overexpression of <i>yerP</i>, <i>ycxA</i> and <i>ycxA-efp</i> had little or negative effects on surfactin synthesis, suggesting YfiS is involved in surfactin efflux. By replacing the native promoter of the <i>srfA</i> operon encoding surfactin synthase with three promoters, surfactin synthesis was significantly reduced. However, knockout of the global transcriptional regulator gene <i>codY</i> enhanced the surfactin titre to 1601.8 ± 91.9 mg/L. The highest surfactin titre reached 3.89 ± 0.07 g/L, with the yield of 0.63 ± 0.02 g/g DCW, after 36 h of fed-batch fermentation in 5 L fermenter. This study provides a reference for further understanding surfactin synthesis and constructing microbial cell factories.