Productivity improvement and biochemical characterization of xylanase from rice straw by Trichoderma

Abstract

Trichoderma reesei F418 has a potential for xylanase production using rice straw (RS) as carbon source under solid state fermentation conditions (SSF). A hyperproducing fused isolate Trichoderma reesei F418FS was obtained after UV-mutagenesis followed by intra-specific protoplast fusion. The optimized SSF conditions for maximum xylanase production by T. reesei F418FS (6875 IU/gDW) was achieved at pH 7.0, 35oC and 90% moisture content at the 5thday of incubation. A major xylanase isoenzyme was purified to homogeneity and has molecular weight of 33 kDa, optimum pH at 5.0, stable at pH ranged from 3.5 to 8.0, optimum temperature for activity at 50oC with activation energy (Ea) 22.93 Kcal mol-1 (5.48 KJ mol-1) and stable at temperature up to 70oC. T. reesei F418FS xylanase exhibited a high specificity towards xylans with a low activity for cellulosic substrates such as avicel cellulose and carboxymethyl cellulose which concluded that T. reesei F418FS xylanase can be described as a cellulase-free xylanase. The Km values for T. reesei F418FS xylanase are 2.8, 2.65 and 7.7 mg ml−1 for BiWX, BeWX and OSX, respectively. T. reesei F418FS xylanase slightly stimulated by monovalent cations K+ and Li+, inhibited by Hg2+ and also inhibited by Cu2+, confirmed the presence of at least sulfhydryl group in the active site of the enzyme. The inhibitory effect of EDTA suggested that T. reesei F418FS xylanase is a metalloprotein. T. reesei F418FS xylanase can be described as an acidic cellulase-free xylanase, has a possible application in biobleaching in paper and pulp industry.

Key Words: Xylanase, Trichoderma reesei, UV-mutagenesis, intraspecific protoplast fusion, rice straw, agroindustrial waste, purification and characterization.