Analysis Of The Degradation Effect Of Neurospora Crassa CBH Overexpression Strain

How to degrade straw efficiently,reasonably and effectively is the primary problem to be solved in waste recycle,straw as the biggest producer of agricultural waste has been listed as one of the most important biological energy.Neurospora crassa could produce cellulase to degrade straw though with low efficiency.In this paper,3 CBH genes of cellulase were selected and over-expressed so that they could be used in straw degradation of corn,rice,wheat and sorghum.First the solid state fermentation method was used to testify the changes of cellulase activity with CBH deletion strains.The results showed that the cbh-2over-expressed strain was more suitable for degradation of corn and rice,and the cbh-1over-expressed strain was suitable for wheat,and the gh6-3 over-expressed strain could degrade sorghum better.Further the degrading conditions were optimized based on single factor and orthogonal experimental design.The optimum conditions for the cbh-2 over-expressed strain to degrade corn straw was: the corn straw's particle size was 70 mesh,the initial pH was 5.5,the fermentation temperature was at 30?,and 14 days fermentation.While the cbh-2 over-expressed strain was more likely to degrade rice straw as following condition: the straw's particle size was 80 mesh,the initial pH was 5,the fermentation time was 13 days,the fermentation temperature was at 28?.The wheat straws were degraded by the cbh-1 over-expressed strain more efficacy as: the straw's particle size was 80 mesh,the initial pH was 5.5,the fermentation time was 14 days,the fermentation temperature was at 28?.And the sorghum straw's best degradation by gh6-3 over-expressed : the straw's size was 90 mesh,the initial pH was 5,temperature was at 30? for 13 days fermentation.Based on the results of optimization the degrading system of 4 types of straws were established.After 7day's fermentation,the highest CBH activity were detected,they were 45.57U/mL for corn straw degradation,37.98U/mL for rice straw,34.59U/mL for wheat and 40.15U/mL for sorghum straw respectively.The degradationrate of straws of corn,rice,wheat and sorghum could reach up to47.92%,38.93%,33.01%,41.27% corresponding to their CBH activity.The surface of the straw could be seen clearly under the SEM micrograph,straw fibers were broken down and became loose that made further degradation happen.