Abstract: A bacterial strain BQ₂ that could rapidly produce lipopeptides was isolated from the production water from Xinjiang Oilfield. Phylogenetic analysis of the homoeologous 16S rRNA gene sequences showed that BQ₂ shared a 99% sequence similarity with Bacillus amyloliquefaciens. When cultured with 20 g·L^-1 of glucose and 5 g·L^-1 of sodium nitrate as carbon and nitrogen sources, BQ₂ decreased the surface tension of culture medium from 69.7 mN·m^-1 to 25.9 mN·m^-1 within 8 h. The rapid increase in the production of biosurfactant occurred within 20-24 h, and the highest yield of 655.4 mg·L^-1 was detected at 40 h. Analyses from thin layer chromatography (TLC) and infrared spectroscopy (IF-TR) revealed that the biosurfactant produced by BQ₂ is lipopeptide with cyclic structure. This biosurfactant had a critical micelle concentration (CMC) of 30 mg·L^-1, and showed good emulsifying activity (EI₂₄) against various organic compounds such as crude oil from Xinjiang Oilfield. The surface activity of the fermentation broth of BQ2 remained stable under a wide range of temperature (20-121 ℃), salinity
(30-250 g·L^-1  of sodium chloride), and pH (4-12), respectively. Strain BQ₂ could rapidly produce high yield biosurfactant, with a good environmental stability and this presents a possible great potential in microbial enhanced oil recovery or environmental remediation processes.

Key words: phosphorus balance, phosphorus use efficiency, Chinesecabbage, phosphorus threshold, oasis irrigation region.