One man’s poop is another man’s gold

Gold is one of humanities most valued and. it has been instrumental to the birth of societies and civilisations, and it has many uses today beyond pure aesthetic looks.

‘Pot of gold’ Credit: Jeremy Schultz

Since the birth of early civilisations gold has been valued as currency. Its relative rarity and low melting point meant it was an ideal currency. It was a material which was rare enough to be valuable, lustrous and unique making it easily identifiable and distinguishable from other metals, didn’t rust and thus maintained shape and form, and easily formed into recognisable coins or currency. It was, and still is the ideal measurement of wealth and has been an intrinsic quality of humanity’s history, spurring exploration and conquest to obtain this mesmerising material.

Today gold is used in every industry from dentistry and jewellery to electronics and computers. Gold is incredibly ductile (able to be stretched into wires) and a great conductor of heat and electricity, making it perfect for electronics. However golds primary use is for Jewellery, which uses about 75% of all gold produced due to its ability to be formed into rings and other jewellery in a variety of colours.

Consequently, due to its versatility and aesthetic value gold is one of the most expensive metals, almost twice the price of platinum (around 29 thousand USD per kg compared to golds 47 thousand USD per kg) This is especially surprising given that platinum is orders of magnitude rarer than gold. The balance claims that In 2018 ‘ 3,332 tons of gold and about 165 tons of platinum were mined globally’.

The most common types of gold are Auric chloride (Gold(III) chloride) and chloroauric acid, both require heat and chemical refinement to produce pure gold.

So, what if there was a way to produce this precious and highly valued metal instead of mining it?

c. metallidurans can produce small gold nuggets. Credit: American Society for Microbiology

In 2018 scientists from Martin Luther University Halle-Wittenberg, the University of Adelaide in Australia, and the University of Munich discovered a bacterium that absorbs toxic metal-based compounds and produces or ‘poop’ out gold.

The bacterium C. metallidurans can absorb compounds such as gold chloride (a neurotoxin to humans found in nature) and produce 99.9% pure gold. The bacteria, somewhat predictably, lives in heavy metal-enriched soil, naturally converting these toxic metals such as lead and gold into their pure metallic form.

Naturally occurring gold or ‘primary gold’ (created through geological movements bringing gold ore to the surface) undergoes significant weathering, forming toxic gold compounds which are useless for industrial applications and require significant refinement to produce pure gold ore. However, C. metallidurans naturally converts these toxic gold particles into ‘secondary gold’ or inert, pure gold.

The exact methodology for how this bacterium converts the decomposed minerals into pure metal is unknown, however, the general process is understood. Gold compounds enter the same way as copper – copper is a vital compound for the bacterium, however, it is toxic at high concentrations – both the copper and gold are converted into a form which is easily absorbed by the bacteria, however then the concentrations of copper and gold are too high, the bacteria converts it back into its original metal form and excretes it, thus producing gold ‘nuggets’ which can then be collected.

Although the mass production of gold from through the recycling of toxic gold compounds and this bacterium is unfeasible as current industrial mining operations can produce significantly more raw gold ore at a lower cost, this bacteria does provide an opportunity to refine gold from ores that contain only trace deposits.


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One Response to “One man’s poop is another man’s gold”

  1. Daniel Fry says:

    Bacteria seem to hold the answers to lot of problems and they do some of the most interesting things! These bacteria may not have much use in gold production, but they might be useful somewhere else. Great post