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A stable long-life tannase was synthesised by Fusarium subglutinans and the fermentation processing parameters were optimised. Maximum enzyme production (9.38 U/ml) was recorded after 96 h of incubation at 35°C, initial pH 5, in submerged culture (200 rpm) utilising 2% (w/v) tannic acid as a sole carbon source. The tannase produced was purified to electrophoretic homogeneity through two-step column chromatography and the purified form remained stable in a pH range of 6-8. Its midpoint of thermal inactivation (T m ) was recorded at 70°C after 60 min of exposure. Maximum tannase activity was enabled at pH 6 and 40°C. Ca 2+ , K + , Mg 2+ and Mn + showed a stimulatory effect while Ba 2+ , Co 2+ , Cu 2+ , Fe 3+ and Zn + showed a competitive inhibitory effect on enzyme activity. Values of K m , V max , K cat and the molecular mass of the purified enzyme were 0.116 μM ml −1 min −1 , 3.57 mM, 1.16 μM ml −1 min −1 and 150 kDa, respectively. The participation of the SH group and carbohydrates in the enzyme structure was also suggested by the results. The stability of the purified and partially purified enzyme at −15°C extended to 13 months.

Cellulase producing fungus Chaetomium cellulolyticum NRRL 18756 was subjected to various doses of gamma irradiation to enhance the production of the industrially important enzyme carboxymethyl cellulase (CMCase). Among all the mutants tested, M-7 obtained through 0.5 KGy irradiation showed highest extracellular CMCase production which is 1.6-fold higher than 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, 2.5mM MgSO4, and 0.05% (v/w) Tween 80. Optimal moisture content and initial pH was 40% (v/w) and 5.0-6.5, 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 words: Chaetomium cellulolyticum; Carboxymethyl cellulase; Mutation; Optimization; Solid state fermentation DOI: http://dx.doi.org/10.3329/bjb.v40i2.9769   Bangladesh J. Bot. 40(2): 139-147, 2011 (December)