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There’s gold in them there bacteria

Scientists have found that the bacterium, Cupriavidus metallidurans, can transform toxic gold compounds to metallic gold, according to research by Reith and colleagues published online on the 7th October in the journal PNAS.

Bacteria are naturally found on gold particles from the earth’s surface; but it is unclear, and controversial, as to whether bacteria have an active role in the formation of these gold particles (biomineralisation). An international team of scientists (from Australia, USA, Canada, Germany, Belgium and France) investigated a metallophilic (metal resistant and able to grow on heavy metals) bacterium called Cupriavidus metallidurans, which forms biofilms (a slimy layer of bacteria stuck together) on grains of gold. They found that C. metallidurans accumulates toxic gold complexes (containing Au III ions) from solution inside the bacterial cell, this accumulation is increased in metabolically active (i.e. living) bacteria. The toxic gold complexes activate bacterial genes involved in the combat against oxidative stress (damage in cells caused by reactive oxygen species, which includes unpaired electrons aka free radicals), and for metal resistance. Also, an uncharacterised cluster of genes which are specifically linked with resistance to gold were activated. Bacteria were then able to detoxify these gold complexes, ultimately turning them into harmless nanoparticles of gold. Similar gold nanoparticles were also seen in bacterial biofilms on grains of gold.

C. metallidurans containing a gold nanoparticle. Reith et al (PNAS 2009).

C. metallidurans containing a gold nanoparticle. Reith et al (PNAS 2009).

The scientists used some very fancy and expensive equipment for their work; including synchotrons at the European Synchotron Radiation Facility (ESRF) and the Advanced Photon Source (APS). Synchotrons are a type of particle accelerator that produces very intense beams of X-rays (1000 billion times brighter than X-rays in hospitals). They were used by the scientists as a super-microscope to see gold particles inside C. metallidurans in great detail.

These findings provide evidence that bacteria in the environment may contribute to the formation of grains of gold, which in turn could form gold nuggets. Gold is a rare and precious metal and these bacteria could be used as a tool to help mineral explorers find new gold deposits.

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