Characterization of a β-xylosidase produced by a mutant derivative of Humicola lanuginosa in solid state fermentation

The production of extracellular beta-xylosidase by a newly isolated mutant derivative of Humicola lanuginosa M7D on lignocellulosic substrates and xylan was maximized in solid state fermentation by adopting a search technique varying one parameter at a time. The H. lanuginosa mutant achieved maximum production of beta-xylosidase (728 IU g(-1) substrate, Y-P/S) when grown on Vogel's medium containing xylan, followed by medium containing corncobs (669 IU g(-1)) supplemented with corn steep liquor (initial pH 6.5, moisture level 75%) at 45 degrees C. Purified mutant-and parent-derived enzyme exhibited K-m values of 1.8 and 2.0 mM, respectively. Both enzymes were optimally active at pH 8.5 and a temperature of 60 degrees C. Both enzymes displayed high thermostability, with a half-life of 2.9 and 0.9 min, enthalpy of denaturation (Delta H*) of 102.1 and 110.10 kJ mol(-1), entropy of denaturation (Delta S*) of -38.5 and -4.5 J/mol K, and free energy of denaturation (Delta G*) of 115.7 and 111.7 kJ/mol at 80 degrees C for the mutant- and parent organism-derived enzymes, respectively. The kinetic and thermodynamic properties suggest that the beta-xylosidases from both strains are superior to several previously reported enzymes from other thermophilic species, and may have potential applications in various industrial fields.