Screening,Identification And Breeding Of A Candida Yeast Producing Alkline Lipase And Studying On Its Fermentation Conditions

Twenty-two strains which hydrolyze olive oil on the primal agar plates containing olive oil were isolated from the 160 soil samples via to repeating isolate. Among these strains some are molds and the others are yeasts , through describing with optic microscope and analysis of the morphology of colony . Bacteria nearly cann't be found for the reason of adding Streptomycin in the enrichment medium . All of these strains were purified by repeating lining on the agar plates.Preponderate over one decade strains were isolated from the 42 strains , their diameter ratio between digest zone and colony (D/d) on the primal agar plates are over one point five , all of them are activated and then rescreening through testing their enzyme activities by Potentiomatric Titration . There are 12 strains whose lipase activity came to 40U/mL under the culture condition of 40℃ and pH 9.0 . One strainvs enzyme activity of them was the highest and came to 63.3U/mL, and coded L₃₀ , it's heredity was fixedness during the repeating subculture . At the same time, studying showed the enzyme is a alkaline lipase . Utilizing themorphology , physiology and biochemistry methods ,we identified it as Deuteromycotin , Blastoymcates , Cryptococcccus the Candida amylolenta .To improve L3Ovs lipase yield , it was treated by the routine U.V. and NTG. On the base of conventional mutation , for the more it was treated with the Na-succinic and Nystatin , Na-succinic is the structure analogy of its metabolization, but Nystatin can enhance the penetration of the cell wall. Seven yeasts whose diameter ratio between digest zone and colony were found, and the lipase activity produced by them have enhanced patently on the agar plates than that of I^o, by several ground disposing and screening . At last, by rescreening with test enzyme activity , a high yield strain was selected , its enzyme activity came to 94U/mL and coded L30-UNN. After six subculture and testing its heredity proved to be stabilization. Later , we studied L3o-UNNvs conditions optimization of fermentation and producing lipase .The optimization experiment about fermentation medium composition and culture conditions have showed lipase produced by yeasts L30-UNN is a induced enzyme , carbon sources and pH have great impact on its lipase yield, the optimal seed age is between 18h and 24h . The optional medium composition for thes strain producing alkaline lipase is(%): soybean meal 4, sucrose0.5, olive oil 2, (NH4)2SO4 0.1, K2HPO4 0.2, MgSO4.7H2O 0.03, its enzyme activity of fermentation aqueous solution came to 97U/mL under the condition of 28 °C and aeration rate of 170rpm culture for 72h . The lipase activity was 50% higher than that of the original strain.