Experts calculated that base metals like zinc, copper and nickel will become scarce in the near future. This research project explores an innovative cost-effective technology that not only remove metals from process streams and waste waters, but that additionally also yields recyclable metal products, with minimum environmental impact. We will investigate the potential to reduce elemental sulfur (S0) to hydrogen sulfide by microbes at extreme conditions: low (20-30°C) and high temperature (70-80°C) and low pH (2-4). The challenge is to develop a high-rate microbiological process that is stable and scalable. We will address both biotechnological and microbiological aspects: 1) selectivity, rate and stability of sulfur reduction under extreme conditions in bioreactors, 2) physiology and molecular ecology of the microbes involved and 3) microbe-sulfur interaction of isolates from bioreactors.