Evaluation of oil displacement potential of genetically engineered strain WJPAB fermentation broth

Rhamnoolipids are the most widely studied and used biosurfactants, which can be used in microbial flooding to enhance oil recovery. Pseudomonas aeruginosa is the main species of rhamnoolipids synthesized at present. In this study, wild strain WJ was modified by directional genetic engineering, and the strong promoter PoprL was used to replace the original promoter of rhlAB gene, and the genetically engineered strain with increased copy number of Popr-Rhlab gene was constructed, which was named as the genetically engineered strain WJPAB. The optimal carbon source of WJPAB was rapeseed oil. Under the optimal fermentation conditions, the product yield of WJPAB was 57.83g/L, which was 91.17% higher than that of wild strain WJ.The metabolites of strain WJPAB are purified and analyzed by high performance liquid chromatography mass spectrometry (HPLC-MS). The products are confirmed to be rhamnose homologues, including 3 single rhamnose homologues and 5 double rhamnose homologues. The physical and chemical properties of the metabolites of strain WJPAB were studied, and it was found that the metabolites of strain WJPaB had good surface/interfacial activity, which could reduce the surface tension of water to 27.34 mN/m, and change the surface of oil-wet core from oil-wet surface to water-wet surface. The emulsification index of simulated oil, cetane and liquid paraffin is above 60%. In addition, bacterial metabolites have good stability and can maintain good surface activity even at pH 3–11, salinity 0–20g/L and temperature 120 °C, and can adapt to a wide range of reservoir environmental conditions. In the oil displacement experiment, a compound oil displacement system is established by combining fermentation broth and xanthan gum. The compound system can increase the recovery rate by 15.45%, save the separation and purification process of biosurfactant, and reduce the application cost. The results show that Pseudomonas aeruginosa WJPAB has a good application prospect in the microbial oil recovery field.