The microorganism Cupriavidus metallidurans appears to be immune to elevated concentrations of heavy C. metallidurans can produce small gold nuggets. Source: American Society for MicrobiologyC. metallidurans can produce small gold nuggets. Source: American Society for Microbiologymetals. Instead of succumbing to exposures that would be toxic to other organisms, the rod-shaped bacterium has developed a way to extract valuable trace elements from a brew of heavy metals without poisoning itself. It is also unique in its ability to produce gold nuggets.

The mechanism by which this seemingly alchemic achievement occurs has been discovered by researchers from Martin Luther University Halle-Wittenberg (MLU), the Technical University of Munich (TUM) and the University of Adelaide in Australia.

On contact with copper and gold, which usually occurs in a form that is difficult to be bioaccumulated, C. metallidurans converts them to a form that is considerably easier for import.

When too much copper has accumulated inside the bacteria, it is normally pumped out by the enzyme CupA. The researchers observed that the enzyme is suppressed in the presence of gold, so that toxic copper and gold compounds remain inside the cell. As a defense, the bacteria activate another enzyme — CopA, which transforms the copper and gold compounds into their originally difficult-to-absorb forms.

The gold compounds that are difficult to absorb transform in the outer cell area into harmless gold nuggets only a few nanometres in size.

In nature, C. metallidurans plays a key role in the formation of so-called secondary gold, which emerges following the breakdown of primary gold ores. It transforms the toxic gold particles formed by the weathering process into harmless gold particles, thereby producing gold nuggets.

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