Alkali-tolerant β-glucosidase produced by newly isolated Aspergillus fumigatus WL002 from rotten wood

• An alkalophilic lignocellulosic decomposing fungus WL002 was isolated and identified.
• A β-glucosidase gene was cloned from newly isolated A. fumigatus WL002.
• β-glucosidase purified from E. coli had pH optima in the alkaline range.
• Enzyme displayed the higher activity against p-nitrophenyl-β-d-glucopyranoside.
• Alkali β-glucosidase was a likely catalyst for biodegradation of cellulosic biomass.

A lignocellulosic decomposing fungus WL002 with a high β-glucosidase activity was isolated from rotten wood. The fungus was classified and designated as Aspergillus fumigatus WL002 through morphological and internal transcribed spacer sequence (ITS) analysis. A putative β-glucosidase gene, bglW, which was cloned from the isolated strain by PCR amplification, consists of an open reading frame of 2517 nucleotides and encodes a polypeptide containing 838 amino acids with a catalytic domain that belongs to the glycosyl hydrolase family 3. The bglW gene was successfully expressed in Escherichia coli Rosseta and the expressed product exhibited a molecular weight of 92.2 kDa through SDS-PAGE. The optimal pH and temperature of the activity of the purified recombinant enzyme BglW with salicin were 9.0 and 50 °C, respectively. BglW was sufficiently stable at pH 8.0- pH 9.5 and at 40 °C −50 °C. BglW also retained >75% of its original activity after 0.5 h of pre-incubation. BglW exhibited the highest activity against p-nitrophenyl-β-d-glucopyranoside with a specific activity of 484.3 ± 13.5 U mg−1, followed by esculin, salicin and o-nitrophenyl-β-d-galactopyranoside. By contrast, the enzyme was inactive to carboxymethyl cellulose sodium, phosphoric acid-swollen cellulose and Avicel. BglW was also stable in most of the tested metal ions and chemical reagents. Results suggest that the alkaline β-glucosidase BglW is a possible candidate for the biodegradation and bioconversion of cellulosic materials.