Abstract

AIMS: To determine the role of fungal metabolites in the desorption of metals.

METHODS AND RESULTS: Desorption of Zn from charcoal by three different fungi was compared against metal desorption with reverse osmosis water, a 0.1% Tween 80 solution and a 0.1 mol l(-1) CaCl(2) solution. All three fungal filtrates desorbed three times more Zn than either 0.1% Tween 80 or 0.1 mol l(-1) CaCl(2). Metal chelator production in Trichoderma harzianum and Coriolus versicolor was constitutively expressed while chelator production in Trichoderma reesei was induced by Zn. The presence of Zn inhibited the production of metal chelators by C. versicolor. Only C. versicolor was found to produce oxalic acid (a strong metal chelator). All fungi caused a marked decrease in pH, although this was not enough to explain the increased desorption of the metals by the different fungal filtrates.

CONCLUSIONS: Metal chelation via organic acids and proteins are the main mechanisms by which the fungal filtrates increase zinc desorption.

SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study explain why plants inoculated with T. harzianum T22 take up more metal from soil, than noninoculated plants while metabolites produced by fungi could be used for metal leaching from contaminated soils.