Ten fungal species were isolated from decomposing wood in the Amazon forest. All produced xylan-degrading enzymes when cultivated in liquid media containing oat spelt xylan. The best producing strains were identified as Penicillium corylophilum, Aspergillus niger and Trichoderma longibrachiatum. The best yields of β-xylosidase and α-arabinofuranosidase activities were Trichoderma harzianum and Trichoderma sp. Xylanase activities from crude extract samples of P. corylophilum, A. niger and T. longibrachiatum were partially characterized. They were most active at 40°C (A. niger) or 45°C (P. corylophilum and T. longibrachiatum) and pH 4.0-4.5. Reducing agents (β-mercaptoethanol and dithiothreitol), L-cysteine and L-tryptophan activated xylanase activity. In addition, dithiothreitol improved the half-lives of these enzymes at 50°C and 60°C. By contrast, N-bromosuccinimide inhibited all the enzyme activities. Xylan and dithiothreitol afforded protection against xylan-degrading enzyme inactivation by N-bromosuccinimide, but failed to reverse it. The apparent Km values on soluble and insoluble xylans from oat spelt showed that xylan-degrading enzymes from A. niger, T. longibrachiatum and P. corylophilum were most active on the soluble form. © 2003 Elsevier Ltd. All rights reserved.
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