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영어

Production cost of cellulases is critical for the effective cellulosic ethanol production processes. A fast-growing cellulolytic fungus Penicillium decumbens has been isolated in our laboratory in 1979. It has a well balanced lignocellulose degrading enzyme system. The higher productive and catabolite-derepression mutants (JU-A10 and JU-A10-T) were isolated by mutagenesis and screening. The mutants have been successfully used to produce cellulase preparations and cellulosic ethanol in industrial or pilot scale in China. Higher cellulase activity was achieved by optimizing culture conditions of the strain and composition of production medium with corncob residue (CCR) from xylitol industry as the substrate. The cellulase activity reached 18.9 IU/ml and the cost of cellulase fermentation was reduced. To learn how cellulase production was regulated, genome sequencing of wild type strain 114-2, resequencing of JU-A10 and JU-A10-T genomes were performed to identify the difference in their genomes. The genome size is about 30 Mb, containing 9984 putative genes. 23 genes were found having CBM1 (carbohydrate binding module 1), which is highest number comparing with other known cellulase producing fungi. The digital gene expression tag profiling and Fluorescent Difference 2D Gel Electrophoresis were used to analyze the gene expression patterns and transcriptomics of P.decumbens strains grown in medium containing cellulose-wheat bran or glucose. More than 7 million tags were sequenced for each RNA sample.
When P.decumbens was grown in medium containing cellulose as carbon source, transcripts of many cellulases and hemicellulases were expressed at higher levels relative to glucose-grown cultures. Up-regulated genes in the presence of wheat bran included: genes encoding various biomass-degrading enzymes, such as cellobiohydrolases, endoglucanases, β-glucosidase, swollenin, xylanases, arabinosidase, esterases, α-amylase, chitinase and cutinase. It was found that a single nucleotide deletion occurred in the gene of CreA, a repressor of cellulase and xylanase expression, in the mutants, and it was confirmed to be the reason of derepression. Our analysis will provide genome-wide insights into the changes in P. decumbens mutants. The results provided valuable information for the study on the mechanism of cellulase synthesis in P.decumbens. The cellulase and cellulosic ethanol production processes were studied to etermine the optimal techniques for cellulase fermentation and related parameters for alcohol fermentation, in order to provide reference for industrialization of cellulosic ethanol in China.