Screening Of Oil-producing Strains

Microbial oils is usually known as single-cell oil, referring to oils synthesised bymicroorganisms utilizing carbohydrates and hydrocarbons in vivo, and the content of oilcan achieve more than20%in cells.The demand of oil has increased significantly because of the more and morepopulation and the growing shortage of natural resources. Meanwhile, the limiteddevelopment of traditional oils and fats industry leads to the increase of thecontradiction between supply and demand of oils. Therefore, searching a new oilresource--microbial oils using renewable resources as raw materials has a greatsignificance for people on meetingt the demands of oils.In this paper, thermal-acid method was determined as the method for screeninghigh-yield strains of oil by comparing methods of Soxhlet extraction and thermal-acid.The extraction conditions were optimized by single factor and orthogonal experiments.The results were as follows: dry cell0.5g, hydrochloric acid volume7mL, heat treatingtime8min, alcohol volume5mL, aether-petroleum ether20mL, extraction22min.After Cryptococcus SP-11was treated by UV-irradiation and diethyl sulfate etc, astrain ULi5-2producing oils with high yield and genetic stability, was successfullyobtained. The biomass, oil yield and oil content of the mutant reached19.12g/L,11.09g/L,58.01%respectively, which improved by21.71%，49.06%，22.54%more thanbefore. Analyzed by gas chromatography, the fatty acid compositions of CryptococcusULi5-2were oleic acid, linolic acid, cetylic acid, stearic acid and linolenic acid, whichwere similar to the vegetable oils.The culture medium and the fermentation conditions of the strain ULi5-2wereoptimized by single-factor experiments. The optimum culture conditions for oilsproduction were as follows (g/L):glucose140, glycerol0.5, sodium citrate2, corn steepliquor3, KNO31, K2HPO4.3H2O2, MgSO4.7H2O1, MnSO4.H2O0.002, CaCl20.0003,FeSO4.7H2O0.0025, ZnSO4.7H2O0.0008; inoculation time24h, inoculation amount10%, initial pH7.0, temperature28℃, rotation speed180rpm, broth’s volume30mL/250mL in shake flask, culture time96h. Under the optimum condition, thebiomass, oil yield and oil content of strain ULi5-2reached30g/L，60%，18.36g/L,which improved by56.90%，3.43%，65.55%respectively.The kinetic models of cell growth, product formation and substrate consumption were established basing on the experimental date of batch fermentation byCryptococcus ULi5-2in5L fermentation reactor. The non-line fitting was employed tomodel the kinetics of fermentation by software OriginPro8.0. The results showed thatthe values of model calculations and experimental value of batch fermentation fittedwell, the dynamic models could describe the parameter changes of CryptococcusULi5-2in fermentation process well.