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

Abstract

The production of extracellular β-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 β-xylosidase (728 IU g−1 substrate, YP/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°C. Purified mutant- and parent-derived enzyme exhibited Km values of 1.8 and 2.0 mM, respectively. Both enzymes were optimally active at pH 8.5 and a temperature of 60°C. Both enzymes displayed high thermostability, with a half-life of 2.9 and 0.9 min, enthalpy of denaturation (ΔH*) of 102.1 and 110.10 kJ mol−1, entropy of denaturation (ΔS*) of −38.5 and −4.5 J/mol K, and free energy of denaturation (ΔG*) of 115.7 and 111.7 kJ/mol at 80°C for the mutant- and parent organism-derived enzymes, respectively. The kinetic and thermodynamic properties suggest that the β-xylosidases from both strains are superior to several previously reported enzymes from other thermophilic species, and may have potential applications in various industrial fields.