Screening. Of Cellulase Highly Producing Strains By Mutation Treatment And Fermentation Condition Optimization

After the spores of penicillium decumbens A10 ,the initial strain, was treated by U.V.and High-energy ion beams, a penicillium decumbens A-135 with high cellulase activity was screened. The enzymatic activity of the mutant strain kept stable after 10 generations. Then the A-135 was treated by 30keV N+ with dosage of 5×1015 N+/cm2, a high production strain K79 was obtained. On the condition of unoptimized cluture medium, the Filter Paper Activity(FPA) of the fermentation broth was improved from 25.5 IU/mL to 40.8 IU/mL which was 60% higher than the initial strain and shows fine stability.Single-factor experiment was carried out on the amount of wheat bran, peptone, surfactant and VC which was the bases of the culture medium for producing cellulase by the mutant strain K79 on the optimum condition, After orthogonal designing experiment, the optimized fermentation conditions of penicillium decumbens K79 were obtained, the test proportion was as following: wheat Bran 2%, corn straw powder 3%, KH2PO40.3%,(NH4)2SO40.2%,CO(NH2)20.05%,MgSO40.05%,CaCO30.5%,peptone 0.1%,tween-80 0.015mL/100mL,VC 0.01%. On this circumstance, the FPA of the mutant strain K79 reached 55.5IU/mLunder the optimized conditions.Different fermentation temperature, different initial fermentation pH and different airflow were studied during the enzyme producing process. The results showed the optimum conditions for producing cellulase by the mutant strain K79 were 32℃, pH6.8 and 30mL/250mL flask. The mutant strain K79 and the initial strain A10 were all exhibited the same kinds of CMCase and FPA activities, the CMCase and FPA of the mutant strain were higher than those of the initial strain.Cellulase of the initial strain A10 showed optimal enzyme activities at pH 5.4 ,while the K79 is pH 6.0. Enzymatic activity of the mutant strain K79 is stable at the range of pH 6.0～10 ,while the initial strain A10 is for pH 7.0～10. Cellulase for both K79 and A10 exhibited optimal activities at 52℃and showed better stability with the temperature of 20℃- 50℃. The temperature for lost of halfactivity ( t1/2 ) for both strains was around 55℃.