A recent study has described how a metal eating bacteria, Cupriavidus metallidurans, manages to digest toxic metal compounds to produce minuscule gold nuggets.
Transforming a toxic metal into gold is apparently a piece of cake for Cupriavidus metallidurans. Among their multiple roles in life on earth, it appears that there are certain microbes that are also expert at purifying precious metals. An international team of researchers have recently highlighted how this bacteria, discovered in 2009, manages to produce gold by digesting toxic metal compounds.
Much like multiple other elements, gold follows a biogeochemical cycle: it dissolves, moves and deposits as sediment in the earth. The microbes, which are of paramount importance to life on earth, are also implicated in each step of this process. So, how is it that the bacteria are not poisoned by the highly toxic compounds? How do they ‘detox’ these elements?
C. metallidurans prosper in soils that contain hydrogen and an array of toxic heavy metals. For one thing, this signifies that there is little competition with other organisms, which are easily poisoned in such an environment. “If an organism chooses to survive here, it would have to find a way to protect itself against these toxic substances”, explains microbiologist Dietrich H. Nies from the Martin Luther University in Halle-Wittenberg, Germany, and the main author of the study.
He claims that the bacteria possess a fairly ingenious protection mechanism, which involves not only gold, but also copper. The components of these two elements can easily penetrate the C. metallidurans cells. Once they have penetrated the bacteria, they interact in such a way that the copper and gold ions are transported deeply inside the bacteria, where they could potentially wreak havoc. But in order to tackle this problem, the bacteria use enzymes to move the incriminating metals outside of their cells.
The enzyme that does this with copper is called CupA. But the presence of gold leads to a new problem: “When the components of gold are also present, the enzyme is deleted and the toxic compounds in the copper and gold stay inside the cell“, explains Nies. At this stage, other bacteria would probably simply give up and go and live in a less toxic environment, but not C. metallidurans. This organism in fact possesses another enzyme which works in its favour, which scientists have labelled CopA.
With this molecule, the bacteria can convert the components of copper and gold into components that can be more easily absorbed by the cells. “The bacteria is less poisoned, and the enzyme that deals with the copper can then eliminate the excess copper unhindered”, says the researcher. Not only does this process allow the microbe to get rid of all the undesirable copper, but it then results in the formation of minuscule microparticles of gold, in the form of nuggets, on the surface of the bacteria.
In nature, C. metallidurans also play a role in the formation of what we call ‘secondary gold’, which emerges following the decomposition of geologically created primary gold ores. It transforms the toxic gold particles formed by the weathering process into harmless gold particles, thus producing gold nuggets.
As well as this incredible ability to apparently thwart nature, this bacteria’s biological prowess could be put to good use. Understanding how C. metallidurans can eject golden nuggets could allow researchers to lift the veil on the biogeochemical cycle of gold. The precious metal in ores that contain only small quantities of this metal could thus be purified without the need for toxic mercury bonds, as was previously the case.
You can find further details of this study in the journal Metallomics.