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Carbohydrate oxidases in ericoid and ectomycorrhizal fungi: a possible source of Fenton radicals during the degradation of lignocellulose

Published online by Cambridge University Press:  01 August 1998

R. M. BURKE  and
J. W. G. CAIRNEY
R. M. BURKE
Affiliation:
Department of Biomolecular Sciences, UMIST, PO Box 88, Manchester M60 1QD, UK
J. W. G. CAIRNEY
Affiliation:
Mycorrhiza Research Group, School of Science, University of Western Sydney (Nepean), PO Box 10, Kingswood, NSW 2747, Australia
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Abstract

Isolates of the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf et Kernan, and the ectomycorrhizal fungi Suillus variegatus (Swartz ex Fr.) and Pisolithus tinctorius (Pers.) Coker & Couch, along with a Cortinarius sp. and the white rot Phanerochaete chrysosporium Burdsall were examined for the ability to oxidize carbohydrates to their corresponding lactones and to excrete the H2O2 produced thereby. All except Phanerochaete chrysosporium were found to express cellobiose oxidase (cellobiose dehydrogenase, EC 1.1.19.88) and glucose oxidase (β-d-glucose[ratio ]oxygen 1-oxidoreductase, EC 1.1.3.4) when grown on cellobiose and glucose respectively. Production of extracellular H2O2 was visualized during growth on both substrates using ABTS as the chromogen. According to the Fenton reaction, H2O2 will react with hydrated or chelated Fe(II) in the environment to produce hydroxyl (Fenton) radicals, HO·. Mycelial extracts from each of the mycorrhizal fungi produced HO· in the presence of cellobiose and Fe(II), presumably mediated by H2O2 produced by cellobiose oxidase activity in the extracts. Conditions favourable to HO· production were shown to exist in Modified Melin–Norkrans medium, and the data discussed in relation to previously observed lignin degradation by mycorrhizal fungi.

Keywords

Mycorrhizal fungiFenton's reagenthydroxyl radicalslignocellulose degradation
Type
Research Article
Information
The New Phytologist , Volume 139 , Issue 4 , August 1998 , pp. 637 - 645
Copyright
© Trustees of New Phytologist 1998

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