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White and brown rot fungi

Stereum gausapatum, Bleeding Oak Crust, a white rot fungus © Dirk Hoffmeister

Basidiomycetes (usually species from the subphylum Agaricomycotina) are the only known aerobic microbes capable of degrading wood. This material mainly consists of cellulose and hemicelluloses which are polyglycosides, encrusted by lignin which is a three-dimensional network built of phenylpropanoid units. This composite polymer is the most abundant and the most recalcitrant organic material on earth.

Fomes fomentarius, Tinder Fungus, a white rot fungus © Dirk Hoffmeister

White rot fungi like Phanerochaete chrysosporium preferably attack lignin, leaving behind a bleached material, mainly crystalline cellulose. To achieve this decomposition of lignin, they secrete a unique constellation of degradative enzymes. With the aid of the typical lignin-modifying enzymes, such as lignin peroxidase, manganese peroxidase, versatile peroxidase, and phenol-oxidases of the Laccase type they literally thrive on woody materials. Environmental contaminants, such as polychlorinated biphenyls, pentachlorophenol, and polycyclic aromatic hydrocarbons, are also attacked, if they possess chemical structures similar to lignin. As a result, they are crucial to soil mineralisation and the circulation of carbon from the atmosphere into organisms and back again.

Calocera viscosa, Yellow Stagshorn, a brown rot fungus © Dirk Hoffmeister

Brown rot fungi like Piptoporus betulinus (birch polypore, of which Ötzi the Iceman carried fruiting bodies with him) preferably attack the polysaccharide portion of wood and do not produce significant activities of lignin-degrading enzymes.