Specific metal sequestering acidophilic fungi

Abstract

Sixty acidophilic fungi isolated from the Tinto River (pH between 2 and 2.5 and high concentration of heavy metals) selected on the bsis of their taxonomic diversity were exposed to increasing concentrations of selected metals (Ag + , Hg 2+ , Cu 2+ , Zn 2+ , As 5+ , Cr 3+ , Ni 2+ and Cd 2+ ) to determine their resistance and sequestering profiles. Some of the isolates were extremely sensitive to the different metals assayed, while others were capable of growing in the presence of metal concentrations as high as 0.4 M. In general, the acidophilic fungi from the Tinto River are more resistant to heavy metals than the reference systems obtained from type collections, exhibiting a characteristic polyresistance profile which is extremely variable. Some of the fungi can sequester heavy metals with rather high efficiency. Metal sequestering is normally associated with metal resistance. In several cases specific heavy metal sequestering was observed. Preliminary data obtained with P34, a Penicillium isolate, suggested that the mechanism of specific copper sequestering (33% at 100 mM of Cu 2+ ) depends on active cell growth, involving metal transport and formation of cellular inclusions. The amount of metal absorbed in non growing or disrupted cells was rather low. The copper sequestering specificity of P34 was maintained in the presence of complex metal mixtures of industrial bioleaching solutions. The potential applications of these fungi in biohydrometallurgy are discussed.