SOLUBILIZATION OF SOME NATURALLY-OCCURRING METAL-BEARING MINERALS, LIMESCALE AND LEAD PHOSPHATE BY ASPERGILLUS-NIGER

The ability of the soil fungus Aspergillus niger to tolerate and solub ilise seven naturally occurring metal-bearing minerals, limescale and lead phosphate was investigated. A. niger was able to solubilise four of the test insoluble compounds when incorporated into solid medium: c uprite (CuO2), galena (PbS), rhodochrosite (Mn(CO3)(x)) and limescale (CaCO3). A. niger was able to grow on all concentrations of all the te st compounds, whether solubilisation occurred or not, with no reductio n in growth rate from the control. In some cases, stimulation of growt h occurred, most marked with the phosphate-containing mineral, apatite . Precipitation of insoluble copper and manganese oxalate crystals und er colonies growing on agar amended with cuprite and rhodochrosite was observed after 1-2 days growth at 25 degrees C. This process of oxala te formation represents a reduction in bioavailability of toxic cation s, and could represent an important means of toxic metal immobilisatio n of physiological and environmental significance.