Kinetics studies of the partially purified cellulase produced during the degradation of rice husk pre-treated at different phs using Mucor indicus

Abstract

This study was aimed at the production of cellulase from the degradation of rice husk using a fungi species isolated from rice husk dump site. Rice husk was pre-treated at 120°C in a mineral nutrient medium at different pH 2, 7 and 12. After the pre-treatment the pH of the different media was adjusted to 7 which was suitable for microbial growth. Mucor indicus isolated from the rice husk dump site was inoculated into the pre-treated husk media and the set-up was allowed to stand for 28 days with periodic shaking. At the expiration of the 28 days, the broth was filtered and centrifuged at 4000 rpm for 20 min to remove all cell suspension. Cellulase was isolated using 90% ammonium sulfate saturation. The yield of cellulase produced were 14.81, 13.43 and 26.74% with specific activity 1.415, 23.237 and 15.524 m mg−1for pH 2, 7 and 12, respectively. After gel filtration the yield of cellulase produced was 0.71, 6.01 and 12.10% with specific activity of 0.114, 22.365 and 19.320 m mg−1for pH 2, 7 and 12, respectively. The Vmax of crude cellulase produced were 0.81, 2.10 and 2.84 μmol min−1while the Km were 46.30, 42.21 and 47.72 mg mL−1for pH 2, 7 and 12, respectively. The Vmax: Km ratio were 0.0176, 0.0497 and 0.0594 mL mg−1for pH 2, 7 and 12, respectively, which showed that the cellulase produced at pH 12 will be more efficient in the hydrolysis of cellulose to glucose. This was also demonstrated by the catalytic efficiency of the enzyme at pH 12 (3.57×10−4). The result also showed that cellulase extracted from rice husk pretreated at pH 12 possesses high catalytic efficiency when compared with other pHs.