Partial purification and characterization of a highly thermostable and <i>p</i>H stable endoglucanase from a newly isolated <i style="">Bacillus</i> strain M-9

Abstract

Cellulases to be employed for lignocellulose bioconversion for biofuel (ethanol) industry or for production of other specialty chemicals must be extremely robust to withstand harsh industrial conditions like extremes of temperature, <i>p</i>H, presence of inhibitory agents etc. In the present study the <i style="">Bacillus</i> strain M-9 isolated from decomposing rice bran produced significant amount of endoglucanase after 72 h of fermentation. Endoglucanase was partially purified by ammonium sulphate precipitation (20-50% saturation) and characterized for few properties. The endoglucanase showed activity over broad range of temperatures (30-100^oC) with maximum activity at 60^oC. The enzyme retained 50 and 39% of the maximum activity at 90 and 100^oC, respectively. The enzyme was thoroughly stable at 50-70^oC for 30 min-1 h. The endoglucanase showed activity over a wide range of <i>p</i>H (3-10) with maximum activity at <i>p</i>H 5. Detergents (SDS, Tween 80), metal ions (Zn²⁺, Pb²⁺) and EDTA caused little to moderate reduction in enzyme activity. The endoglucanase was purified to the extent of 9.06 folds by salt precipitation and DEAE-cellulose chromatography. Endoglucanase showed molecular weight of approximately 54 kDa as examined by SDS-PAGE. High thermostability and acid/alkalistability of the endoglucanase reflect potential commercial significance of the enzyme.