Abstract
Evidence for the utilization of reduced forms of antimony, arsenic, copper, hydrogen, manganese, and selenium as energy sources for bacteria is summarized. Each of these, except arsenic in the form of arsenite, can supply energy to appropriate organisms during growth. Arsenite oxidation may be able to provide maintenance energy. A rationale is presented to explain why prokaryotes but not eukaryotes can avail themselves of inorganic energy sources.