Book excerpt: Biomining is the use of microorganisms in the recovery of metals from ores. During bioleaching, metals such as copper, nickel or zinc are oxidized through microbial action from the water-insoluble sulfide to the soluble sulfate forms. Although gold is inert to microbial action, microbes can also be used in gold recovery from certain types of ores because as they oxidize the ore, they open up its structure, thereby allowing a gold-solubilizing agent such as cyanide to penetrate the ore. The book describes several industrial bioleaching and biooxidation processes as well as the underlying theory and biology of the microbes involved.