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Potential applications of lignocellulose-decaying fungi in waste treatment

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Lignocellulose of plant biomass represents the greatest pool of organic carbon on earth. Basidiomyceteous fungi capable of causing different kinds of lignocellulose decay are important biomass recyclers, thereby transforming lignocellulose of plant biomass into soil humus matter. In these organisms, this is done by an extracellular machinery which generates different kinds of strong oxidants, including organic radicals, different species of activated oxygen, as well as highly reactive oxidation states of certain metals. This allows an unspecific attack on different molecular structures of lignocellulose, finally leading to mineralisation, mass reduction, and formation of humic substances. Due to this inspecificity, also a broad variety of organic pollutants is degraded. Such degradation involves mineralisation, incorporation into fungal biomass, and oxidative coupling to soil organic matter.

White-rot and litter-decaying fungi are capable of decomposing lignin, leaving a white residue enriched in cellulose. This feature is attributed to extracellular enzymes such as laccase (EC 1.10.3.2.), manganese peroxidase (EC 1.11.1.13), lignin peroxidase (EC 1.11.1.14), and manganese-independent peroxidase (peroxidase, EC 1.11.1.17), key enzymes of fungal ligninolytic systems (Figure 1) (Fahr et al., 1999; Schlosser et al., 1997).

There are numerous reports on the biodegradation of pollutants of the environment by white-rot fungi. Among those are recalcitrant xenobiotic compounds such as pentachlorophenol, polycyclic aromatic hydrocarbons (PAH), explosives (2,4,6-trinitrotoluene [TNT]), polychlorinated biphenyls (PCB) or chlorinated pesticides (dichlorodiphenyl trichlorethane [DDT] and lindane) (Fahr et al., 1999; Hofrichter et al., 1998; Martens et al., 1996; Scheibner et al., 1997). In various reports, the involvement of ligninolytic enzymes in the respective degradative processes has been proposed (Grey et al., 1998; Hofrichter et al., 1998; Scheibner et al., 1997).

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