Use of a Mixture of Thermophilic Enzymes Produced by the Fungus Thermoascus aurantiacus to Enhance the Enzymatic Hydrolysis of the Sugarcane Bagasse Cellulose

Abstract

Problem statement: The production of hydrolytic enzymes by T. aurantiacus has been performed under solid-state fermentations using lignocellulosic materials. The influences of the inoculum size and of the fermentation medium on the production of hemicellulases and cellulases were studied. Filtrates from the cultures were used to hydrolyze a pulp of sugarcane bagasse and the produced enzymes were shown to be candidates for use as co-adjuvants in plant saccharification. Aproach: The present study focuses on the effect of different culture conditions on production of cellulases and hemicellulases by T. aurantiacus. It is also provides a possible application of T. aurantiacus enzymes in the degradation of sugarcane bagasse pulp, considering that this thermophilic fungus is a potential source of thermostable enzymes. Results: T. aurantiacus was cultivated on four different agricultural residues: sugarcane bagasse, sugarcane straw, wheat straw and corn cob. Xylanase was produced with much more expressive activity than cellulases. The highest titre of xylanase was obtained on sugarcane straw at 9 days (1679.8 IU g⁻¹); the same was observed for β- glucosidase (29.9 IU g⁻¹) at 6 days. With an inoculum load of 10⁸ spores g⁻¹, the amount of exoglucanase produced by the fungus considerably exceeds that produced with 10⁴ spores g⁻¹. Xylanases and cellulases purified from filtrates of the cultures were investigated to hydrolyze a bagasse pulp prepared with alkaline peroxide. Xylanase or sulphuric acid were used as pretreatments for xylan removal, increasing the cellulase performance on pulp bagasse. However, results revealed that the removal of hemicellulose is not the only main factor limiting the cellulose hydrolysis. Conclusion: Results indicate that the xylanase action on alkaline-pretreated sugar cane bagasse enhances the cellulolytic effect promoted by a commercial cellulase. This study thus presents an evaluation of the applicability of enzymes from Thermoascus aurantiacus to potentially improve the enzymatic cellulose hydrolysis.