Evaluation of novel fungal cellulase preparations for ability to hydrolyze softwood substrates - evidence for the role of accessory enzymes

Seven fungal cellulase preparations from Trichoderma and Penicillium spp. were evaluated for their ability to hydrolyze the cellulose component of lignocellulose samples prepared from softwoods by steam explosion or organosolv pretreatment. Hydrolysis was quantified using two indices: mean specific rate and specific conversion. The activities of the cellulase preparations on model cellulosic substrates (filter paper, carboxymethylcellulose and Avicel) were also determined, together with their beta-glucosidase, xylanase, pectinase, galactomannanase and beta-glucanase activities. The ability of a cellulase preparation to hydrolyze pretreated softwood showed little correlation with its activity on filter paper, carboxymethylcellulose and Avicel; however, there was a significant correlation with its level of endogenous beta-glucosidase and xylanase activity. Differences in the performance of the various cellulase preparations were substantially reduced following supplementation with a commercial beta-glucosidase preparation from Aspergillus niger. In addition to beta-glucosidase, this preparation was shown to contain significant levels of endogenous xylanase activity. It appears that the levels of endogenous beta-glucosidase and xylanase are important factors in determining the ability of a cellulase preparation to hydrolyze pretreated softwood and that deficiencies in the levels of both enzymes can be compensated by supplementation with corresponding activities present in the beta-glucosidase preparation. Presumably, P-glucosidase improves cellulose hydrolysis by reducing end-product inhibition by cellobiose, while xylanase activity increases the accessibility of cellulose to cellulases. (c) 2005 Elsevier Inc. All rights reserved.