Silver tolerance and silver accumulation of microorganisms from soil materials of a silver mine

Summary Silver-tolerant microoganisms were isolated from soil materials of a silver mine. The bacterial count decreased approximately linearly with increasing silver concentration. The fungal count, however, remained almost constant in all flasks, up to a concentration of 1 mM silver. At 10 mM Ag⁺ (about 1 g/l) and more, neither bacterial nor fungal growth could be observed.All silver-tolerant isolates were tested for silver accumulation capacity. Bacteria accumulated a mean 23 mg Ag⁺/g dry weight, hyphomycetes 6.7 mg/g dry wt. and yeasts 0.46 mg/g dry wt. The accumulation process of the hyphomycete with the highest accumulation capacity (20 mg/g dry wt.) was shown to be completed after about 30 min. Between 4°C and 80°C the process was nearly independent of temperature; as to the optimum pH, a slight preference for the neutral range was observed. Mycelium destroyed by formaldehyde solution showed the same accumulation pattern. These results would indicate a binding of silver to the surface of the cell.