Discovery of Glycoside Hydrolase Enzymes in an Avicel-Adapted Forest Soil Fungal Community by a Metatranscriptomic Approach

To discover the structural and functional novel glycoside hydrolase enzymes from soil fungal communities that decompose cellulosic biomass, transcripts of functional genes in a forest soil were analyzed. Pyrosequencing of the Avicel and wheat-amended soil cDNAs produced 56,084 putative protein-coding sequence (CDS) fragments, and the most dominant group of putative CDSs based on the taxonomic analysis was assigned to the domain Eukarya, which accounted for 99% of the total number of the putative CDSs. Of 9,449 eukaryotic CDSs whose functions could be categorized, approximately 40% of the putative CDSs corresponded to metabolism-related genes, including genes involved in carbohydrate, amino acid, and energy metabolism. Among the carbohydrate-metabolism genes, 129 sequences encoded glycoside hydrolase enzymes, with 47 sequences being putative cellulases belonging to 13 GH families. To characterize the function of glycoside hydrolase enzymes, we synthesized the putative CelA gene with codon optimization for heterologous expression in Escherichia coli, which was shown to be similar to the structure of plant expansins, and observed stimulation for cellulase activity on Avicel degradation. This study demonstrated that fungal communities adapt to Avicel and wheat decomposition and that metatranscriptomic sequence data can be reference data for identifying a novel gene.