Screening Of Mutant Strains Producing High Levels Of Cellulase And The Study On Its Fermentation Conditions And Characteristics

Lignocellulosic biomass is the largest renewable resource on the earth. With the declin-ing fossil fuels reserve and acceleration of climate change, utilization of lignocellulosic bio-mass such as agricultural straws to obtain fermentable sugar for producing biofuel and bio-products is an effective way to alleviate energy shortage, protect environment and maintain sustainable economic development. Cellulase as the enzyme for liberating sugars from lig-nocellulose has drawn increasing attentions in biofuel and bioproduct development. Additi-onally, cellulase has been widely applied in various industries such as food, textile, chemica-1, papermaking, extraction of Chinese traditional medicine, animal feed etc. The high cost and low activity however, have been the bottleneck in the applications of cellulase, especial-ly for producing biofuel and bioproducts. Therefore, enhancing cellulase production throug-h screening hyperproducing strains has great significance for large scale industrial applicat-ions of cellulase.In this thesis research, a high yield strain H16was obtained after mutagenesis of wide type strain of Penillium piceum9-3by using DES procedures. The cellulase production of the H16was four times more than that of its parent under the unoptimized conditions. The cellulase production of the mutant strain remained stable after6generations.Single-factor experiment was used to optimize the fermentation conditions of H16. The results showed that the optimal carbon source was avicel, nitrogen source was corn-steep powder, initial pH was5.5, culture temperature was30℃, and the volume of fermentation medium was30mL in250mL shake flasks. Under the optimized conditions, the Filter Paper Activity (FPA) and the β-glucosidase activity of the mutant strain H16reached7.41IU/mL and52.96IU/mL, respectively after5d.Studies on the enzyme properties indicated that the optimum pH and temperature of the enzyme reaction were5-5.5and50-55℃, respectively. Enzymatic activity of the H16was stable at the pH range of4.0-6.5, but it was sensitive to high temperature, as only50%enzyme activity remained after24h at50℃. When the crude cellulase of H16was added to the fermentation broth of Trichoderma reesei RUT C30, its hydrolysis efficiency on filter paper (FPA) and steam-exploded corn stover increased substantially.