Accumulation of Heavy Metals by Fungi

Elevated concentrations of toxic metals can occur in the fruitbodies of basidiomy-cetes in polluted environments, and soil saprotrophic and mycorrhizal fungi have been frequently proposed as suitable biomonitors of metal pollution (Kalac and Svoboda 2000; Collin-Hansen et al. 2002; Baldrian 2003). The extent of accumulation of individual metals is species or strain specific, with the high levels of metal enrichment in fungal fruitbodies serving as evidence of the high metal tolerance of fungi. Also, several soil saprotrophic basidiomycetes (e.g., the members of the genera Agaricus, Coprinus, Lepista, Lycoperdon, Marasmius, or Mycena) have been found to be accumulators of heavy metals (Mejstrik and Lepsova 1993; Svoboda et al. 2006). Fruitbodies of Armillaria mellea, collected from metal-polluted soils near motorways, contained several parts per million of Cd and Pb and tens of parts per million of Zn. Cd accumulated with a concentration factor of 32, while Zn and Pb were excluded, with the concentration in sporophores reaching 30-40% of that in the topsoil (Cuny et al. 2001). In another study on soil saprotrophic species (Coprinus, Lepiota, Marasmius, and Armillaria), the concentration factors were found to be between 4 and 100 for Cd and Cu (Poddubny et al. 1998).

The transport of heavy metals between the substrate and fungal fruitbodies occurs in both directions. Cd and Hg tracers applied to the fruitbodies of Agrocybe aegerita were partially translocated into the substrate (wheat straw) and into consecutive harvests (Brunnert and Zadrazil 1979). The accumulation of heavy metals by fungi is not limited to their transport into fruitbodies. As mentioned above, the rhizo-morphs of cord-forming fungi can also accumulate heavy metals, as do the fungal mycelia in soil. The saprotrophic fungi forming the so-called fairy rings, Mycena, Psathyrella, Marasmius, and the Lycoperdaceae, accumulate Ag or Cs. In a fairy ring transect, Cs concentrations correlated with ergosterol (Anderson et al. 1997).

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