Plant cell wall proteins called expansins are thought to disrupt hydrogen bonding between cell wall polysaccharides without hydrolyzing them. We describe here a novel gene with sequence similarity to plant expansins, isolated from the cellulolytic fungus Trichoderma reesei. The protein named swollenin has an N-terminal fungal type cellulose binding domain connected by a linker region to the expansin-like domain. The protein also contains regions similar to mammalian fibronectin type III repeats, found for the first time in a fungal protein. The swollenin gene is regulated in a largely similar manner as the T. reesei cellulase genes. The biological role of SWOI was studied by disrupting the swo1 gene from T. reesei. The disruption had no apparent effect on the growth rate on glucose or on different cellulosic carbon sources. Non-stringent Southern hybridization of Trichoderma genomic DNA with swo1 showed the presence of other swollenin-like genes, which could substitute for the loss of SWOI in the disruptant. The swollenin gene was expressed in yeast and Aspergillus niger var. awamori. Activity assays on cotton fibers and filter paper were performed with concentrated SWOI-containing yeast supernatant that disrupted the structure of the cotton fibers without detectable formation of reducing sugars. It also weakened filter paper as assayed by an extensometer. The SWOI protein was purified from A. niger var. awamori culture supernatant and used in an activity assay with Valonia cell walls. It disrupted the structure of the cell walls without producing detectable amounts of reducing sugars.

The cellulase and hemicellulase genes of the filamentous fungus Trichoderma reesei have been shown to be under carbon catabolite repression mediated by the regulatory gene cre1. In this study, strains were constructed in which the cre1 gene was either completely removed or replaced by a truncated mutant variant, cre1-1, found previously in the Rut-C30 mutant strain with enhanced enzyme production capability. The T. reesei transformants with either deletion or truncation of cre1 had clearly altered colony morphology compared with the parental strains, forming smaller colonies and fewer aerial hyphae and spores. Liquid cultures in a medium with glucose as a carbon source showed that the transformants were derepressed in cellulase and hemicellulase production. Interestingly, they also produced significantly elevated levels of these hydrolytic enzymes in fermentations carried out in a medium inducing the hydrolase genes. This suggests that cre1 acts as a modulator of cellulase and hemicellulase gene expression under both noninducing and inducing conditions. There was no phenotypic difference between the ⌬cre1 and cre1-1 mutant strains in any of the experiments done, indicating that the cre1-1 gene is practically a null allele. The results of this work indicate that cre1 is a valid target gene in strain engineering for improved enzyme production in T. reesei.The filamentous fungus Trichoderma reesei (Hypocrea jecorina) produces large amounts of extracellular enzymes. The majority of the secreted proteins are various plant polymerdegrading enzymes; the most abundant of these enzymes are the cellobiohydrolases and endoglucanases that act synergistically to break down cellulose. This fungus has been used as a production host for various industrial enzymes, including products tailored for textile, feed, food, and pulp and paper applications (6, 10). It has been reported that protein production levels in the industrial T. reesei process exceed 100 g/liter (7).The major cellulase and hemicellulase genes are regulated in a coordinate manner by the carbon source available (2, 9, 14). Cellulose and other plant materials and other substances (for example, lactose) induce the expression of cellulase and hemicellulase genes, while glucose acts as a repressing carbon source. Several genes coding for regulators of cellulase and hemicellulase expression have been isolated. These include CREI mediating carbon catabolite repression, the repressor ACEI, the activator ACEII, the CCAAT binding complex Hap2/3/5 (reviewed in references 2, 17, and 27) and the activator XYRI (29). The CREI protein has sequence similarity with other fungal proteins mediating glucose repression, such as Aspergillus nidulans CREA (8) and Saccharomyces cerevisiae MIG1 and RGR1 (22). In T. reesei, glucose repression has been shown to occur upon binding of CREI to specific sequences in the cbh1 promoter (13). A mutant cre1 gene (cre1-1) encoding a truncated form of CREI has been isolated from the hypercellulolytic T. reesei strain Rut-C30, which is capable of cel...

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The global feed enzyme market, beneficial effects of feed enzymes on animal production performances; overview on the structure conformation and production of cellulases (β-glucanases) and xylanase enzymes; current enzyme products on the market; developments in the feed enzymes and future trends in the enzyme industry are highlighted in this chapter.

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