A biosurfactants-producing strain QS-M2 could be isolated from the water samples of Daqing Oilfield by a series of steps including hydrocarbon enrichment culture

streak separation

hemolytic activity assay and phenol sulfuric acid assay and so on. The strain was identified as pseudomonas aeruginosa by analysis of 16S rDNA gene and physiochemical methods. Thin-layer chromatography（TLC） and high performance liquid chromatography with mass spectrometry （HPLC-MS） examination showed that the key components of the crude biosurfactant were identified as rhamnolipid species containing two major monorhamnolipid species of Rha C10C10 and RhaC12C12 and three major dirhamnolipid species of Rha2C14C12

Rha2C10C12 and Rha2C10C10. The strain produced crude biosurfactant makes the interfacial tension of water decrease from 72 mN/m to 36. 9 mN/m and has excellent emulsifica- tion property which was stable within 72 h. The present study states that the rhamnolipid biosurfactants are major factors of QS-M2 strain in microbial enhanced oil recovery.