Abstract

Geomycology: mineral-metal transformations by fungi

In terrestrial environments, important mechanisms of fungal metal mobilization from minerals and soil components are acidification and ligand-promoted dissolution mediated by, e.g. organic acid anions. However, if oxalic acid is produced, metal oxalate minerals may result, and these may in turn form carbonates. Such processes can occur in the root region of plants growing on toxic metal minerals as well as in soil and rock-inhabiting fungal communities. Free-living and mycorrhizal fungi are capable of toxic metal mineral transformations and this can be related to fungal metal tolerance and the phosphorus status of the soil. In providing the plant host with phosphorus, fungal solubilization of inorganic phosphates (e.g. Zn3(PO4)2) can result in release of associated toxic metals increasing metal toxicity. However, some mycobionts demonstrate the ability to re-precipitate released metals (Cu, Zn, Pb) within insoluble secondary mycogenic minerals making them chemically stable and unavailable for the plant host and soil biota. Such phenomena are components of geochemical cycles for metals but are also relevant to revegetation/reclamation of metal-polluted sites. Each of these component topics (i.e.. molecular biological and mineralogical processes; mineral dissolution/formation; metal speciation) requires an understanding of fungal growth, function and interactions with the environment at scales ranging from the nano- and sub-micron level through the micron level (e.g. thigmotropic responses of the hyphae to substratum structure), to the centimetre and >metre level (e.g. interactions between colonies, mycorrhizal symbioses, bioremediation strategies). A combined experimental-modelling approach has been very useful in understand such processes across these scales.