The microbiological oxidation of iron and sulfur constitutes two key processes in mineral biotechnology. Both mesophilic and thermophilic bacteria have been described which can utilize inorganic compounds of Fe and S as electron donors (3, 5, 6). At present, although thermophiles are characterized by superior oxidation rates, only mesophilic iron- and sulfur-oxidizing acidophiles are used in large-scale leaching processes for metal recovery from sulfide ores.