Highly Thermostable Xylanase of the Thermophilic Fungus Talaromyces thermophilus: Purification and Characterization

A thermostable xylanase from a newly isolated thermophilic fungus Talaromyces thermophilus was purified and characterized. The enzyme was purified to homogeneity by ammonium sulfate precipitation, diethylaminoethyl cellulose anion exchange chromatography, P-100 gel filtration, and Mono Q chromatography with a 23-fold increase in specific activity and 17.5% recovery. The molecular weight of the xylanase was estimated to be 25kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and gel filtration. The enzyme was highly active over a wide range of pH from 4.0 to 10.0. The relative activities at pH5.0, 9.0, and 10.0 were about 80%, 85.0%, and 60% of that at pH7.5, respectively. The optimum temperature of the purified enzyme was 75°C. The enzyme showed high thermal stability at 50°C (7days) and the half-life of the xylanase at 100°C was 60min. The enzyme was free from cellulase activity. K _m and V _max values at 50°C of the purified enzyme for birchwood xylan were 22.51mg/ml and 1.235μmol min⁻¹ mg⁻¹, respectively. The enzyme was activated by Ag⁺, Co²⁺, and Cu²⁺; on the other hand, Hg²⁺, Ba²⁺, and Mn²⁺ inhibited the enzyme. The present study is among the first works to examine and describe a secreted, cellulase-free, and highly thermostable xylanase from the T. thermophilus fungus whose application as a pre-bleaching aid is of apparent importance for pulp and paper industries.