Purification and Characterisation of a Thermostable β-Xylosidase from Aspergillus niger van Tieghem of Potential Application in Lignocellulosic Bioethanol Production

Abstract

A locally isolated strain of Aspergillus niger van Tieghem was found to produce thermostable β-xylosidase activity. The enzyme was purified by cation and anion exchange and hydrophobic interaction chromatography. Maximum activity was observed at 70-75 °C and pH 4.5. The enzyme was found to be thermostable retaining 91 and 87% of its original activity after incubation for 72 h at 60 and 65 °C, respectively, with 52% residual activity detected after 18 h at 70 °C. Available data indicates that the purified β-xylosidase is more thermostable over industrially relevant prolonged periods at high temperature than those reported from other A. niger strains. Maximum activity was observed on p-nitrophenyl-β-D-xylopyranoside and the enzyme also hydrolysed p-nitrophenyl β-D-glucopyranoside and p-nitrophenyl α-L-arabinofuranoside. The purified enzyme acted synergistically with A. niger endo-1,4-β-xylanase in the hydrolysis of beechwood xylan at 65 °C. During hydrolysis of pretreated straw lignocellulose at 70 °C using a commercial lignocellulosic enzyme cocktail, inclusion of the purified enzyme resulted in a 19-fold increase in the amount of xylose produced after 6 h. The results observed indicate potential suitability for industrial application in the production of lignocellulosic bioethanol where thermostable β-xylosidase activity is of growing interest to maximise the enzymatic hydrolysis of lignocellulose.

Discovery of a Novel β-xylosidase with Xylanase Activity and Its Application in the Production of Xylitol from Corncob Xylan

“…It was able to hydrolyze bagasse xylan, oat spelt xylan, birchwood xylan, beechwood xylan, and corncob xylan, and showed its highest hydrolysis activity of 8.16 U/mg for corncob xylan. This finding was significantly different from those reported for β-xylosidases, which exhibited no activity toward xylan substrates [25]. Several β-xylosidases have been found to have additional α-arabinosidase activity [26,27], but β-xylosidases with xylanase activity have rarely been reported and, in such reports, the xylanase activity is very low.…”

Synergistic Enzyme Cocktail to Enhance Hydrolysis of Steam Exploded Wheat Straw at Pilot Scale

“…Other accessory enzymes like hemicelluloses, esterases, arabinofuranosidases, laccases remove the physical protective covering of the cellulase microfibrils thereby, improving the enzyme accessibility (Gonçalves et al, 2015). Since the xylooligomers produced from hemicelluloses inhibit the hydrolysis by either physical blocking of the enzyme or by competitive inhibition of the cellulases; an optimal amount of xylanase is also essential (Qing et al, 2010;Boyce and Walsh, 2018). The commercially available first generation enzyme preparations (like Spezyme CP, Celluclast, and Novozyme 188) have been found to be underperforming in hydrolyzing the xylo-oligomers and overcoming their inhibitory effects at reasonable dosages (Qing et al, 2010;Agrawal et al, 2015b).…”

Computation-Aided Phylogeny-Oriented Engineering of β-Xylosidase: Modification of “Blades” to Enhance Stability and Activity for the Bioconversion of Hemicellulose to Produce Xylose

“…Most studies have been focused on their mining and characterization over the past decade. Generally, the reported β-xylosidases showed some novel properties such as pH stability and thermostability, but very few combined both superior properties. − Nowadays, protein engineering is considered a common and powerful tool for customizing and improving the properties of enzymes for industrial applications . However, there were few protein engineering studies aiming to improve the stability of β-xylosidases in recent years, even though researchers combined DNA shuffling and saturation mutagenesis to enhance the thermal stability of the β-xylosidase XylBH43 or improved the thermostability of β-xylosidase from Selenomonas ruminantium by introducing disulfide bridges. , Ancestral sequence reconstruction (ASR) is a well-established approach used to deduce the evolutionary information on genes and has emerged as a practical protein engineering strategy for generating variants with desirable properties.…”