Uptake of free and complexed silver ions by yeasts isolated from a gold mining industry in Brazil

Damaging effects caused by toxic concentrations of metals in fungi can be avoided by several mechanisms such as accumulation of the metal by cell wall components and extracellular materials, chelation, or precipitation by secreted metabolites, and by intracellular compartmentalization or complexing by low molecular weight proteins (Gadd, 1990). Microbial cells usually have two distinct phases of metal uptake. The first is a metabolism-independent process (biosorption), which involves metal adsorption around the cell envelope (Volesky, 1990). The second is exclusively dependent on cell metabolism and involves active translocation of metals into the cell (bioaccumulation) (Blackwell et al., 1995). However, scant information is available about the toxicity and uptake of metal complexes. Under some conditions the concentration of free metal ions can be reduced in natural or polluted environments by complexing agents.