Genetic improvement of Trichoderma reesei for large scale cellulase production

A strategy based on plate screening tests was designed for the selection of mutant strains of the fungus Trichoderma reesei suitable for cellulase (EC 3.2.1.4) production on an industrial scale. Six mutant generations were successively isolated, each of them fulfilling all of the three criteria: (1) improved productivity compared to the previous one, (2) high stability, (3) ability to be further improved. The mutant ultimately selected, CL 847, exhibited a four-fold increase in cellulase productivity in cellulose media as compared to the starting strain QM 9414, resistance to catabolite repression, increased β-d-glucosidase (EC 3.2.1.21) specific activity and it was partially constitutive. High cellulase concentrations were obtained in simple media with lactose or glucose as sole carbon source. The strain is currently used in an industrial fermentation plant.