Isolation and properties of β-xylosidase from Aspergillus niger GS1 using corn pericarp upon solid state fermentation

Abstract

There is growing interest in developing high-yield and low-cost production of xylanolytic enzymes for industrial applications using agroindustrial byproducts. A native strain of Aspergillus niger GS1 was used to produce β-xylosidase (EC 3.2.1.37) on solid state fermentation using corn pericarp (CP) with innovative alkaline electrolyzed water (AEW) pretreatment at room temperature. β-xylosidase was purified by ammonium sulfate fractionation followed by anion exchange and hydrophobic interaction chromatographies. β-Xylosidase showed a molecular weight of 111kDa, isoelectric point of 5.35 and specific activity of 386.7U (mg protein)−1, using p-nitrophenyl-β-d-xylopyranoside as substrate, at pH 5 and 60°C, and optimal activity at pH 4.5. Optimal temperature was 65°C, showing full activity after 1h at 60°C. Activity was reduced by 1mM β-mercaptoethanol (55.6±0.1%), and enhanced by 1mM SDS (11.0±0.03%). Km and Vmax were 6.1±0.9mM and 1364±105U (mgprotein)−1, respectively, whereas kcat was 5.1s−1. A predominant α-helix (41%) was determined from circular dichroism on β-xylosidase, while thermal transition profiles produced a Tm of 54.1±5.8°C, enthalpy change for unfolding of 67.4±6.7kJ/mol, and onset temperature of 37°C. Pre-treatment of CP using AEW is an ecologically friendly alternative to chemical and heat treatments for the production of relatively high levels of β-xylosidase.