Selection of Bacterial and Fungal Strains for Bioaccumulation of Heavy Metals from Aqueous Solutions

Eighty strains of fungi and heterotrophic bacteria, isolated from natural water sources polluted with heavy metals, were tested for their bioaccumulation abilities. Metal-resistant strains were first selected in a preliminary step. Preselected cultures were then screened for gold, silver, nickel and cadmium uptake capabilities. A collection of bioaccumulating strains, consisting of 39 strains for the recovery of gold, 9 strains for silver, 28 for cadmium and 22 for nickel, has been established. All the strains selected were able to remove metals tested from diluted solutions (ca. 5 mg/l) to levels below 0.5 mg/l. The maximum uptake capacity of strains was determined in concentrated metal solutions (20 - 50 mg/l). Nine of the strains had saturation values of 100 mg/g dry weight or higher. The importance of pH in passive bioaccumulation process is discussed.