Production and characterization of highly thermostable [beta]-glucosidase during the biodegradation of methyl cellulose by Fusarium oxysporum

Production of [beta]-glucosidase from Fusarium oxysporum was investigated during degradation of some cellulosic substrates (Avicel, [alpha]-cellulose, carboxymethyl cellulose (CMC), and methylcellulose). Optimized production of [beta]-glucosidase using the cellulosic substrate that supported highest yield of enzyme was examined over 192 h fermentation period and varied pH of 3.0-11.0. The [beta]-glucosidase produced was characterized for its suitability for industrial application. Methyl cellulose supported the highest yield of [beta]-glucosidase (177.5 U/mg) at pH 6.0 and 30[degrees]C at 96 h of fermentation with liberation of 2.121 [micro]mol/mL glucose. The crude enzyme had optimum activity at pH 5.0 and 70[degrees]C. The enzyme was stable over broad pH range of 4.0-7.0 with relative residual activity above 60% after 180 min of incubation. [beta]-glucosidase demonstrated high thermostability with 83% of its original activity retained at 70[degrees]C after 180 min of incubation. The activity of [beta]-glucosidase was enhanced by [Mn.sup.2+] and [Fe.sup.2+] with relative activities of 167.67% and 205.56%, respectively, at 5 mM and 360% and 315%, respectively, at 10 mM. The properties shown by [beta]-glucosidase suggest suitability of the enzyme for industrial applications in the improvement of hydrolysis of cellulosic compounds into fermentable sugars that can be used in energy generation and biofuel production.