Engineering fungi for boosting cellulase production and its potential industrial application
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Bioconversion of lignocellulosic residues is initiated primarily by microorganisms such as fungi and bacteria which are capable of degrading lignocellulolytic materials. Fungi produce large amounts of extracellular cellulolytic enzymes including endoglucanases, cellobiohydrolases (exoglucanases) and β-glucosidases that work efficiently on cellulolytic residues in a synergistic manner. The ascomycete Hypocrea jecorina (anamorph Trichoderma reesei), an industrial (hemi)cellulase producer, can efficiently degrade plant polysaccharides. However, the biology underlying cellulase hyperproduction of T. reesei, and the conditions for enzyme induction in this organism are not completely understood. In this study, the optimum conditions for cellulase production by T. reesei strains were investigated. Three different strains of T. reesei, including QM6a (wild-type), and mutants QM9414 and RUT-C30, were grown on 7 soluble and 7 insoluble carbon sources, with the latter group including 4 pure polysaccharides and 3 lignocelluloses. Maximum cellulase activity of QM6a and QM9414 strains, for the majority of tested carbon sources, occurred after 120 h of incubation, while RUT-C30 had the greatest cellulase activity after around 72 h. Maximum cellulase production was 0.035, 0.42 and 0.33 μmol glucose equivalents using microcrystalline celluloses for QM6a, QM9414, and RUTC-30, respectively. Increased cellulase production with the ability to grow on microcrystalline cellulose was positively correlated in QM9414 and negatively correlated in RUT-C30.