Improvement of lichenysin production in Bacillus licheniformis by replacement of native promoter of lichenysin biosynthesis operon and medium optimization

Lichenysin is a biodegradable surfactant with huge potential for recovering crude oil from the oil reservoir. The current production of lichenysin is made through fermentation from wild strain of Bacillus licheniformis, which is limited by low yield. The aim of this work was to improve lichenysin-producing capability of a wide strain B. licheniformis WX-02. Lichenysin produced from WX-02 was first extracted, purified, and identified. Through the substitution of the promoter of lichenysin biosynthesis operon, the mutants B. licheniformis WX02-P43lch, WX02-Pxyllch, and WX02-Psrflch were constructed with the constitutive promoter (P43), the xylose-inducible promoter (P ₓyₗ ), and the surfactin operon promoter (P ₛᵣf ), respectively. A consistent change trend was observed between lichenysin production and lchAA gene transcription, confirming the strength of the promoters as an important factor for lichenysin synthesis. Among the three mutants, WX02-Psrflch produced the highest lichenysin yield. The production by the mutant WX02-Psrflch was further improved with the optimization of the major medium components including glucose, NH₄NO₃, and Na₂HPO₄/KH₂PO₄. Under 30 g/L glucose, 5 g/L NH₄NO₃, and 80 mM/60 mM Na₂HPO₄/KH₂PO₄, the strain WX02-Psrflch produced 2,149 mg/L lichenysin, a 16.8-fold improvement compared to that of wild strain WX-02.