from ScienceAlert Website
(American Society for Microbiology)
Amongst their many roles in life on Earth, it turns out some of these microbes are also experts at purifying precious metals.
An international team of researchers has figured out how one metal-gobbling bacterium, Cupriavidus metallidurans, manages to ingest toxic metallic compounds and still thrive, producing tiny gold nuggets as a side-effect.
Just like many other elements, gold can move through what's known as a biogeochemical cycle:
Microbes are involved in every step of this process, which has led scientists to wonder how they don't get poisoned by the highly toxic compounds that gold ions usually form in the soil.
The rod-shaped C. metallidurans was first found to poop gold nuggets back in 2009, when scientists discovered that it somehow manages to ingest toxic gold compounds and convert them into the element's metallic form without any apparent danger to the organism itself.
Now, after years of investigation, Frank Reith and his colleagues finally know the precise mechanism of how the bacterium achieves this amazing feat.
C. metallidurans thrives in soils which contain both hydrogen and a range of toxic heavy metals.
This means the bacterium doesn't have much competition from other organisms that can be easily poisoned in such an environment.
As it turns out, the bacterium has a pretty ingenious protective mechanism, which involves not just gold, but also copper.
Compounds containing both of these elements can easily get into C. metallidurans cells. Once inside, they interact in such a way that copper ions and gold complexes get transported deep inside the bacterium, where they could potentially wreak havoc.
To deal with this problem, bacteria employ 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.
At this point other bacteria might just give up and go live somewhere less toxic, but not C. metallidurans.
This organism has another enzyme up its sleeve, which scientists have labeled CopA (copper resistance protein A).
With this molecule, the bacterium can convert the copper and gold compounds into forms that are less easily absorbed by the cell.
But not only does this process let the microbe shed all that unwanted copper, it also results in teeny tiny gold nugget nanoparticles on the bacterial surface.
The results of this research, which builds on previous work by the same team, are a fascinating insight into the workings of a strange microbe. But on top of that, the bacterium's weird talent could actually be put to a good use.
Understanding how C. metallidurans can poop out gold nuggets means scientists just got a huge step closer to unlocking the biogeochemical cycle of gold.
In the future these insights could be used to refine the precious metal from ores that only contain small amounts of metal - something that's currently a very tricky prospect.
The research (Synergistic gold-copper detoxification at the core of gold biomineralisation in Cupriavidus metallidurans) has been published in Metallomics.