| In this thesis, 9 biosurfactant-producing strains were isolated from Xinjiang Oilfield. A bacteria strain BQ-2 that could rapidly produce lipopeptides was identified. Phylogenetic analysis of the homoeologous 16 S r RNA gene sequences showed that BQ-2 share 99%sequence similarity with Bacillus amyloliquefaciens.When cultured with glucose and sodium nitrate as carbon and nitrogen sources, BQ-2decreased the surface tension of culture medium from 69.7 m N·m-1 to 25.9 m N·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-1was detected at 40 h.Analyses from thin layer chromatography(TLC) and infrared spectroscopy(IF-TR)revealed that the biosurfactant produced by BQ-2 is lipopeptide with cyclic structure. This biosurfactant has a critical micelle concentration(CMC) of the production 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-1of sodium chloride), and p H(4–12), respectively.In order to improve the biosurfactant yield of BQ-2 strain, single factor combined with response surface methodology was used to optimize the culture medium composition and culture conditions. The result is as follows(g·L-1): Molasses 79.41, Na Cl 0.6, KCl 0.6, KH2PO43.75, K2HPO4·3H2O 4.75,Mg SO4·7H2O 0.55, Yeast extract, microelement 2.44 m L, initial p H6.0. Compared to the initial medium and conditions, the optimized medium and conditions increased biosufactant yield about 200% from 616.36 mg·L-1 to 1776.52 mg·L-1.In conclusion, strain BQ-2 could rapidly produce high yield biosurfactant, with a good environmental stability and this presents possible great potential in microbial enhanced oil recovery and environmental remediation processes. |
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