α-l-arabinofuranosidase from an efficient hemicellulolytic fungus penicillium janthinellum capable of hydrolyzing wheat and rye arabinoxylan to arabinose

Abstract

This study reports Penicillium janthinellum strain, producing high levels of α-L-arabinofuranosidase (AFase) as well as other components of hemicelluloytic enzyme system (endoxylanase, β-xylosidase and acetyl xylan esterase) on rice straw and wheat bran containing solidified culture medium. Optimization of culture conditions was carried out using Box–Behnken design of experiment to study the influence of process variables (ammonium sulphate, pH and moisture level) on AFase production. Analysis of data showed R2 (0.9967) and adjusted R2 (0.9925) indicating model to be good fit and robust to predict culture conditions for AFase production. Under optimal culture conditions P. janthinellum produced high levels of AFase (212 units/g dw substrate) in addition to xylanase (1800 units/g dw substrate), β-xylosidase (31 units/g dw substrate), acetyl xylan esterase (231 units/g dw substrate) and feruloyl esterase (27 units/g dw substrate). AFase from P. janthinellum culture extract was purified to homogeneity and characterized to be a 64 kDa protein with a pI of 3.8. The peptide mass fingerprinting showed the AFase belonged to family GH54. The enzyme was optimally active at 50o C at pH 5.5 and its activity was positively modulated in presence of Fe3+ions. The enzyme preferentially catalyzed the hydrolysis of pNP- arabinofuranoside (pNPA) with Km and Vmax of 0.4mM and 260 unit mg-1 protein-1, respectively. Hydrolysis with purified AFase (3.0 units/g substrate) released arabinose from rye arabinoxylans (29.5 mg/g substrate) and wheat arabinoxylan (13.4 mg/g substrate), as the sole product indicating P. janthinellum as the important source of α-L-arabinofuranosidase for bioconversion of agro-residue to value added products.