Cellulase activity of filamentous fungi induced by rice husk

Abstract

The objective of this study was to determine the potential of different filamentous fungi to degrade cellulose in rice husk pre-treated with steam explosion or alkaline hydrolysis. A preliminary test performed with carboxymethyl cellulose and nine fungi (Trichoderma 1, 2, 3, 4, 5; Trichoderma reesei; Aspergillus niger; Rhizopus oryzae and an isolated fungus from rice husk) allowed the selection of the fungi that can degrade cellulose the most. Subsequently, the fastest growing fungi on the substrate (carboxymethyl cellulose) were subjected to a fermentation bioreactor (18 mL of the fungus with 2 mL of conidial suspension at a concentration of 5 x 106 conidia mL^-1). Their potential to degrade cellulose was determined. This was done by measuring the amount of total carbohydrate and reducing sugars using the anthrone method and 3,5 dinitrosalicylic acid respectively. On the other hand, the endoglucanase, exoglucanase and β-glucosidase activity of the two most promising fungus (Trichoderma sp. 1 and Aspergillus sp.) was evaluated. Statistical analysis revealed no significant differences; however, the rice husk pre-treated with steam explosion before the fungal strains had the greatest amount of total carbohydrates; it produces 2.9 and 1.4 times more than those not treated with alkaline hydrolysis. Moreover, fungi Trichoderma sp. 1 and Aspergillus sp. had higher number of total released carbohydrate and reducing respectively, which demonstrated the difference in the enzyme system of the two microorganisms. Endoglucanase and exoglucanase activities had similar performance for Aspergillus sp., and Trichoderma sp. 1, during the 288 h of the test. Likewise, β-glucosidase activity was similar. After 192 h, values of 0.150 and 0.140 IU mL^-1 were obtained for Aspergillus sp. and Trichoderma sp. 1, respectively. Finally, the applicability of rice husk in agribusiness as a raw material for subsequent fermentation and for obtaining added-value compounds is shown.

Keywords: Enzymatic activity, rice husk, fermentable sugar, agroindustrial wastes, filamentous fungi.

African Journal of Biotechnology, Vol 13(45) 4236-4245