Undoubtedly, gold is one of the most precious materials on earth. Besides its common use in art and jewelry, gold is also an essential component of our modern computers and cell-phones.
Cupriavidus metallidurans (previously Ralstonia metallidurans ) type strain CH34 (hereafter C. metallidurans) is a Gram-negative , motile, non-spore forming, rod-shaped bacterium known for its ability to resist toxic heavy metals; metallidurans literally translates to “metal-enduring”. When cultured on trypticase soy agar (TSA) at 30°C for 24h, C. metallidurans forms round, smooth, flat and convex colonies that are transparent and about 0.5mm in diameter. C. metallidurans is a mesophile; it has not been shown to grow under conditions outside of a range of 20-37°C.
This bacteria consist of high number of heavy metal resistance genes and ability to thrive in toxic environments make it an important model organism in studying the mechanisms by which diverse microbes deal with heavy metal stress . C. metallidurans is also able to precipitate solid gold from aqueous gold (III) tetrachloride, which is a potent heavy metal toxin to most organisms
Ecology and Pathology
Cupriavidus metallidurans is normally found in industrial sediments or wastes which contain high heavy metal concentrations . C. metallidurans was initially isolated from the wastewater of a zinc factory in Liège, Belgium . Later, this bacterium was found in another unusual place; it was the dominant organism present in biofilms on gold grains found in the Prophet gold mine in Queensland, Australia . This bacterium is able to survive in these environments due to the abundance of metal-resistance genes dispersed throughout its genome which code for heavy metal exporters, regulators,and potential metal-binding proteins used to detoxify the cell . These abilities have earned C. metallidurans some fame. When placed in an environment containing aqueous Gold (III) chloride, this bacterium reduces the complex – by a mechanism yet to be fully understood – leading to the precipitation of solid gold nanoparticles within the
Cupriavidus metallidurans living in biofilms on gold nuggets. The bacteria detoxify dissolved gold by accumulating it in inert nanoparticles inside their cells.Some biofilms also contained a second species of bacterium Delftia acidovarans.was somehow creating gold particles outside its cell wall, instead of inside as C. metallidurans does.