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Study on the Screening of Biosurfactant-producing Bacteria Strains at Low Temperature and Preliminary Application

Author: LiuChang
Tutor: WangHongYan
School: Northeast Agricultural University
Course: Microbiology
Keywords: Low temperature Biosurfactants Screening Fermentation condition Straw returning
CLC: TQ423
Type: Master's thesis
Year: 2013
Downloads: 43
Quote: 0
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Abstract

Biosurfactants are a kind of effective surface-active compounds mainly produced by microorganisms. In addition to have the same characteristics with chemical surfactants,which have distinct advantages like friendly to environment and reduce costs by using in-situ synthesis. Nowadays, the microorganism which produces the surface active agent is mostly focus on normal temperature bacteria, and the hypothermia microorganisms has few studies. The paper concentrates on the screening of biosurfactant-producing bacteria in the low temperature environment and the optimization of fermentation conditions. Through laboratory simulation of straw returning study, research the effect of low-temperature bacteria and produced biosurfactant on straw degradation, soil chemistry and soil microbiology characteristics. To broaden the biosurfactant application and to clear the straw returning potential application in low temperature environment, carry out the beneficial exploration and attempt. The main results are as follows:Using blood agar plates and blue agar plate as primary screening medium and oil spreading as re-screening method,4strains of cold-adapted biosurfactant-producing bacteria were isolated from the samples, which is from the natural decay of straw in low-temperature environment. The strain B-17with the most ability of biosurfactant-producing had been measured surface tension by secondary screening. With the following morphological characteristics, physiological, biochemical characteristics and16SrDNA sequence analysis, the strain was identified preliminarily as Petrimonas sp..To extract and purify the strain B-17which producing biosurfactant, the results of FT-IR showed that the biosurfactant produced by the metabolic processes of the strain B-17was a kind of glycolipid. Emulsifying capacity measurements of Fermentation broth show that the emulsification activity of fermentation liquor of the strain can maintain75%in5days, which with well solubilizing effect.The fermentation conditions and culture mediums of strain B-17were optimized by single-factor experiment and orthogonal test. The optimal culture medium for biosurfactant-production were as follows(g/L):sucrose20, urea4, Na2HPO41.5, K2HPO41.5, MgSO41, NaCl8. The optimal fermentation conditions for biosurfactant-production were as follows:temperature10℃, initial pH7, the quantity of inoculation8%, volume in conical flask50mL/250mL. With the optimal fermentation conditions,the surface tension of the fermentation broth can fall to27.6mN·m-1from72.0mN·m-1in5 days, which had reduced9.86mN·m-1compared with the initial.The laboratory simulation of straw returning study showed that, adding different amount of the fermentation broth and asepsis fermentation broth can increase the number of soil bacteria and actinomycetes, enhance the enzyme activity including soil urease, invertase, catalase, cellulase and neutral phosphatase, and improve the content of soil nutrient. All of these promote the degradation of straw. in addition, adding amount of the fermentation broth and asepsis fermentation broth which control in30mL/kg is particularly obvious. From the general point of view, the treatment of asepsis fermentation broth has more advantages.

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