Metallophiles and Acidophiles in Metal-Rich Environments

This chapter describes some bacteria that are specifically adapted to metal-rich biotopesand can therefore be considered as a kind of extremophiles. Metal-rich biotopes may be divided up to some extent into natural and anthropogenic biotopes. Natural biotopes correspond to a variety of geological events that often shelter endemic populations of plants (metallophytes). Some deep-sea or terrestrial hydrothermal sources may be also being considered as natural metal-rich biotopes. On their extreme form, anthropogenic metal-rich biotopes are mainly industrial and may be found around metal-processing factories or in dumping sites. They are also characteristic of the Industrial Revolution of the last two or three centuries. Their multiplication on the earth surface has promoted large scale redistribution of bacterial populations. The harsh selection pressure, linked to the chemical mixtures they contain, as likely forced some key genetic rearrangements in these populations and is therefore significant from the point of view of evolution. Ralstonia metallidurans and related species were regularly found from such anthropogenic biotopes. Their resistance to high concentrations of heavy metals as cadmium, chromium, cobalt, copper, mercury, nickel, lead, thallium and zinc is mainly plasmid-borne.