Improvement of carboxymethyl cellulase production from Chaetomium cellulolyticum NRRL 18756 by mutation and optimization of solid state fermentation

Abstract

The purpose of the present investigation was to enhance the production of the industrially important enzyme carboxymethyl cellulase (CMCase) by subjecting the wild cellulase producing fungal strain Chaetomium cellulolyticum NRRL 18756 to various doses of gamma irradiation (0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0 KGy). Among all the mutants tested, M-7 obtained at 0.5 KGy of C. cellulolyticum strain showed highest extracellular CMCase production in a yield 1.6-fold exceeding that of the wild type. Optimal conditions for the production of CMCase by the mutant fungal strain using solid-state fermentation were examined. The optimized medium consisted of sugarcane bagasse supplemented with 1% (w/w) peptone, 2.5 mM MgSO4, and 0.05% (v/w) Tween 80. Optimal moisture content and initial pH was 40% (v/w) and 5.0 to 6.5, respectively. The medium was fermented at 40°C for 4 days. The resulting CMCase yield was 4.0-fold more than that of the wild type strain grown on the basal wheat bran medium. Some characteristics of partially purified CMCase from the mutant and wild type of C. cellulolyticum were investigated. The partially purified mutant CMCase was more stable than the wild type CMCase. Thus, the higher thermostability of mutant CMCase makes it a potential candidate for commercial and industrial process. Key word: Chaetomium cellulolyticum, carboxymethyl cellulase, mutation, optimization, solid state fermentation, characterization.