Demand for mineral products, depletion of high-grade ore deposits, and soaring costs for capital outlay have encouraged developments in hydrometallurgical extraction of metals. The use of bacteria has received much attention as a means for acid production and ferric iron regeneration. Besides thiobacilli, the bacteria commonly associated with leaching operations, another group of microbes with similar functions may play an equally important role in solution mining of copper and other metals. These thermophilic, acidophilic microbes are capable of oxidizing iron, sulfur, and reduced metals at temperatures exceeding 45 deg c. One of the thermophilic microbes, which has been studied extensively in the laboratory, and is referred to as "ferrolobus," oxidizes inorganic iron and sulfur at temperatures between 45 deg and 70 deg c and readily oxidizes molybdenite and copper sulfide minerals in this temperature range. The organism's ability to withstand high concentrations of molybdenum and copper suggests that this organism may be suitable for in situ mining and dump leaching.