Biohydrometallurgy and the environment: Intimate and important interplay

All life forms have absolute requirements for a wide range of metals. For some prokaryotic microorganisms, metals have not only a nutritional requirement but also pivotal roles in energy generation, by acting as electron donors or electron acceptors. In the last half of the twentieth century, scientific technologies emerged that harnessed the abilities of microorganisms to transform metals, and many of these bioprocesses are increasing in scope in the new millenium. This review considers the impact that biohydrometallurgy has on the environment, and vice-versa. The various ways in which microorganisms transform metals, and the continued importance of natural environments as sources of biological systems that have potential in optimising existing operations or for developing new biotechnologies, are described. Abandoned mines are, from a biological perspective, dynamic ecosystems and often develop their own unique complex food webs, in which metals (and sulfur) often play central roles. Finally, the major issue of pollution associated with past and present mining activities is considered, in particular the problem of acid mine drainage. New biologically based approaches that are currently being developed not only to remediate affected water courses, but also to recover metals, are discussed.