We all know the ancient story of the philosopher's stone. For millenia, military men and those of science of various sorts have searched for a substance that could change metals like mercury into gold bullion. Alchemists in the Middle Ages sought to find how is gold made in nature and change it with gold-producing magic. It was also believed to be an elixir of life. That is, something useful for rejuvenation and possibly for achieving immortality.
An international team of researchers have made startling revelations. They have revealed how a soil-friendly bacterium, Cupriavidus metallidurans, can ingest toxic metallic compounds and still thrive. Not only that, but the bacterium also produces tiny gold nuggets as a side-effect.
The article was published in the Royal Society of Chemistry's journal Metallomics. It found how, over time, some minerals break down in the soil containing these bacteria. These minerals change how is gold made in nature. Principally, they release toxic heavy metals as well a hydrogen into their environment.
"Apart from the toxic heavy metals, living conditions in these soils are not bad. There is enough hydrogen to conserve energy and nearly no competition. If an organism chooses to survive here, it has to find a way to protect itself from these toxic substances," explains Professor Dietrich H. Nies, a microbiologist at MLU, in a press release.
Strangely, the bacterium features a unique protective mechanism, which involves not just gold, but also copper.
Science has otherwise identified the collision of two neutron stars as to how is gold produced in nature. In fact, this remains the technically correct answer since bacterium do not produce gold from other elements, but extract it.
To my earlier point, compounds containing both copper and gold can easily get into the bacterium. Once inside, they engage in such a way that copper ions and gold complexes get shifted deep inside the bacterium. There, they could potentially wreak havoc.
To manage this problem, bacteria shoot off enzymes to shift the offending metals out of their cells - for copper, there's an enzyme called CupA. But the presence of gold causes a new problem. "When gold compounds are also present, the enzyme is suppressed and the toxic copper and gold compounds remain inside the cell," according to Nies.
Other bacteria might just wave the white flag and move somewhere less toxic, but not Cupriavidus metallidurans. This organism has another enzyme up its sleeve, which scientists have labelled CopA. With this molecule, the bacterium can change the copper and gold compounds into forms that are less easily absorbed by the cell.
"This assures that fewer copper and gold compounds enter the cellular interior," Niles says. "The bacterium is poisoned less and the enzyme that pumps out the copper can dispose of the excess copper unimpeded." This process lets the microbe get rid of all that unwanted copper. But remarkably, it also results in tiny gold nugget nanoparticles on the bacterial surface.
Realizing the processes involved in this cycle could help revolutionize the way the world extracts gold. This would make the process cleaner and more efficient. As the release states: "The most significant advantages over today’s methods would be the possibility to use poorer ores (with a small percentage of gold) than before and taking mercury and other very toxic compounds out of the extraction process."
In 2013, researchers looked at the germ Delftia acidovorans. They was frequently found it on the surface of tiny gold nuggets. They later revealed that a molecule excreted by the microbe can create "gold biomineralisation," the process by which living organisms produce minerals. In other words the future is exciting for the interaction of precious metals and biology!