This Bacterium Eats Toxic Heavy Metals and Poops Out Gold Nuggets

This living organism definitely takes home the prize for the most valuable excrement in the world.

Move over, alchemists! There’s a new player in town, and it’s not your run-of-the-mill chemical concoction. Meet Cupriavidus metallidurans, the bacterium that can absorb compounds rich in toxic heavy metals, extract gold from them, and poop out tiny gold nuggets. Yes, you read that right. This little guy can turn waste into treasure, and it’s not afraid to get its hands dirty.

C. metallidurans is one tough cookie indeed, living in soil that’s basically a toxic waste dump. As if that weren’t enough, over time certain minerals disintegrate within that messy terrain and discharge toxic heavy metals and hydrogen into their surroundings like an angry volcano. But our friend C. metallidurans just shrugs it off and keeps on living its best life. Talk about resilience!

“If an organism chooses to survive here, it has to find a way to protect itself from these toxic substances,” Professor Dietrich H. Nies, a microbiologist at the Martin Luther University Halle-Wittenberg and lead author of a new study on C. metallidurans, said in a statement. 

Together with his Australian counterpart, Professor Frank Reith from the University of Adelaide, in 2009 Nies was able to prove that C. metallidurans is able to deposit gold biologically as part of the process of protecting itself (maybe we should all take notes here). However, the reasons and exact mechanisms behind this phenomenon remained a mystery – until now.

Both copper and gold are toxic in substantial amounts, and C. metallidurans has chosen copper to depend on for its survival. As noted above, the soil in which it thrives is abundant in toxic heavy metals, which the bacterium metabolizes into a more manageable form like it’s sippin’ on a fancy smoothie.

How? Well, in the event that there is an excessive quantity of copper present, this tough little guy can can bust out its secret weapon, a unique enzyme known as CupA, to kick that excess copper to the curb and keep itself in tip-top shape.

Nevertheless, a curious occurrence takes place when gold is present. Copper gold compounds are like the toxic duo from hell, so our little bacterium friend has to take extreme measures to protect itself. In order to achieve this, CupA is rendered inert and an alternative enzyme, CopA, is activated, turning the copper and gold compounds into something way less absorbable.

“This assures that fewer copper and gold compounds enter the cellular interior,” Nies added. “The bacterium is poisoned less and the enzyme that pumps out the copper can dispose of the excess copper unimpeded. Another consequence: the gold compounds that are difficult to absorb transform in the outer area of the cell into harmless gold nuggets only a few nanometres in size.”

C. metallidurans plays a crucial part in the creation of secondary gold found after the disintegration of primary, geologically formed, ancient gold ores in nature. It converts the poisonous gold particles created during the weathering process into harmless ones, resulting in the formation of shiny, irresistible nuggets of gold! Who says alchemy is a myth?

The study, published in Metallomics, offers valuable understanding about the second half of the bio-geochemical gold cycle, whereby primary gold metal converted by other bacteria into mobile, toxic gold compounds during the first half of the cycle is transformed back into secondary metallic gold. Once the entire cycle is understood, it becomes possible to extract gold from ores with minimal gold content without the use of toxic mercury bonds, which was necessary in the past. What this means in practice is that we soon might be able to get our hands on that sweet, sweet treasure without harming the environment!

Sources: 1, 2, 3, 4