The use of cellulases from a β‐glucosidase‐hyperproducing mutant of Trichoderma reesei in simultaneous saccharification and fermentation of wheat straw

Conidia of the cellulolytic strain Trichoderma reesei F522 were mutagenized with UV irradiation and N ‐methyl|‐ N ′‐nitro‐ N ‐nitrosoguanidine (NTG). A visual agar plate detection system was developed, using esculin and ferric ions, to identify mutants of T. reesei with increased β‐glucosidase activity. Selected mutants were tested for production of extracellular cellulases in shake flasks on autohydrolyzed wheat straw as carbon source. The most active mutant V‐7 showed about 6‐times higher activity of β‐glucosidase than the parent strain F‐522, whereas the filter paper degrading and endo‐1,4‐β‐ D ‐glucanase activities increased by 45% and by almost 31%, respectively. Cellulase preparations obtained from the parent and mutant strains were then used along with Kluyveromyces fragilis cells for ethanol production from ethanol‐alkali pulped straw in the simultaneous saccharification and fermentation (SSF) process. From 10% (w/v) of straw pulp (dry matter), 2.5% (w/v) ethanol was obtained at 43°C after 48 h using cellulase derived from the parent strain of T. reesei. When the β‐glucosidase‐hyperproducing mutant V‐7 was employed, the ethanol yield in the SSF process increased to 3.4% (w/v), the reaction time was shortened to 24 h and no cellobiose was detected in straw hydrolyzates.