Biology

How a hungry, hardy bacteria eats toxic metals and excretes gold nuggets

How a hungry, hardy bacteria e...
German and Australian researchers have figured out how a bacteria called C. metallidurans can consume toxic metals and excrete tiny gold nuggets, like that shown here
German and Australian researchers have figured out how a bacteria called C. metallidurans can consume toxic metals and excrete tiny gold nuggets, like that shown here
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German and Australian researchers have figured out how a bacteria called C. metallidurans can consume toxic metals and excrete tiny gold nuggets, like that shown here
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German and Australian researchers have figured out how a bacteria called C. metallidurans can consume toxic metals and excrete tiny gold nuggets, like that shown here
The C. metallidurans bacteria, along with some of the tiny gold nuggets it excretes
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The C. metallidurans bacteria, along with some of the tiny gold nuggets it excretes

If the goose that laid the golden egg had a real-life counterpart, it would be C. metallidurans. This hardy little bacterium consumes toxic metals and excretes tiny gold nuggets, but how and why it does so has never been fully understood. Now, German and Australian researchers have peered inside the microorganism and figured out that mechanism.

C. metallidurans has carved out a nice little niche for itself, usually living in soils full of heavy metals, which are toxic to most other microorganisms. But this bacteria has evolved a defense mechanism to help it not only survive but thrive under those conditions, and its ability to turn toxic compounds into gold is well known enough to once earn it a place in an alchemy art installation.

"Apart from the toxic heavy metals, living conditions in these soils are not bad," says Dietrich H. Nies, an author on the new study. "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."

The researchers, from Martin Luther University Halle-Wittenberg (MLU), the Technical University of Munich (TUM) and the University of Adelaide, have now identified just how it does that. C. metallidurans needs copper to live, and to extract that trace element from its surroundings the bacteria converts it into a form that's easier to "import."

But there are a few problems. High levels of copper are toxic, and that's not the only heavy metal in the soil. Gold compounds are also imported into its body through the same process. Not only is this natural form of gold pretty toxic, but it's even more potent when mixed with copper.

The C. metallidurans bacteria, along with some of the tiny gold nuggets it excretes
The C. metallidurans bacteria, along with some of the tiny gold nuggets it excretes

To deal with the first problem, C. metallidurans has an enzyme called CupA that pumps out excess copper. When gold and copper are both taken up, the bacteria switches off this enzyme and fires up a different one, CopA. This new enzyme converts the gold and copper back into their original, hard-to-digest forms, effectively solving the second problem.

"This assures that fewer copper and gold compounds enter the cellular interior," says Nies. "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 nanometers in size."

Through this process, C. metallidurans may be responsible for some of the Earth's natural "secondary gold." Primary gold refers to the ancient deposits formed geologically, while secondary gold is much younger, closer to the surface and often found in nugget form. This is often the result of groundwater dissolving primary gold and transporting it upwards, but certain bacteria may also "chew" off tiny flakes of primary gold that then move towards the surface. There, C. metallidurans could convert it into secondary gold, ready for a lucky prospector.

The researchers say that further understanding of this cycle may eventually allow gold to be wrung out of less rich ores, without the need for toxic chemicals like mercury.

The research was published in the journal Applied and Environmental Microbiology.

Source: Martin Luther University Halle-Wittenberg

11 comments
MerlinGuy
Interesting article. It would be nice if this was a scale-able and affordable process.
Jerome Morley Larson Sr eAIA
EXPECT A BIG GOLD RUSH ON SUPERFUND SITES
S Michael
I wonder how it would react in my septic tank?
Charles Barnard
The big benefit will come if we can modify it or it's relatives to deal with detoxifying soils. We really don't need gold, most of it is just reburied in vaults somewhere--bismuth is just as "rare" and perhaps more useful. As always, energy is the key to cleaning or extracting/seperating.
Expanded Viewpoint
Since the bacteria are doing the work of purifying the gold out of the rest of the stuff they feed on, and have been doing so for a very long time all on their own, why do we need to intervene in that process? Why not just focus on collecting their waste products using energy collected from the sun and wind? Optimize their growth conditions and let them get to work!! As to us not needing gold, that fallacy is easily shown to be bunk by just looking at how every fiat paper currency monetary system has collapsed within a few years. And the longer they do last, relatively speaking, the more spectacular the crash when they do crash and fall apart. My paper titled What is Money? fully exposes this insanity that we do not need to have a medium of exchange which has a substantial amount of human labor involved in its creation. Randy
CharlieSeattle
Worth repeating... "The researchers say that further understanding of this cycle may eventually allow gold to be wrung out of less rich ores, without the need for toxic chemicals like mercury."
HoppyHopkins
Sounds like Butte, Montana could use a couple tons of these bacterium in the toxic waters of the pit. That toxic site is so full of heavy copper and other metals that my significant other, to this day, more than 40 years after she moved away, her hair still shows up on x-rays, something that is not normal
Bruce H. Anderson
I recall a Twilight Zone episode where a group of people had stolen a lot of gold, and then used a time machine to transport themselves and the gold into the future. It turned out that their location had become a wasteland, and as time went on the surviving member of the gang finally found civilization. Bedraggled and dying of thirst he pleaded for help saying "I have gold." He then collapsed. One person asked the other "Gold?" The other said, "yes, it used to be a precious metal in the past, but when they learned to synthesize it, it became worth very little." (something like that, it's been a while) Cue music. doodeedoodoo dodeedoodoo.......
kellory
Gold is used in most high end electronics, and all cell phones, (iirc). It has intrinsic value, as well as monetary value, and is also dissolved in the world's oceans. We could ,perhaps, help clean our oceans, as well as gain gold.
Guðni.
The bigger question is can a cupriavidus metallidurans or similar bacteria remove toxic from people. I think that is a question we as humans need answered.