Gold-digging microbe

By spitting out a molecule, a bacterium draws solid gold out of solution

Forget ancient maps and metal detectors. Those seeking hidden gold might do well to add bacteria to their toolbox. The bacterium Delftia acidovorans secretes a molecule that binds to dissolved gold and turns it into shiny, solid gold, scientists have discovered.

The bacterium — and perhaps others like it — might one day process gold at mining sites or create gold nanoparticles with desirable properties, says geomicrobiologist Frank Reith,  a research fellow at the University of Adelaide in Australia.

In 2006 Reith and his colleagues reported finding biofilms of bacteria growing on solid gold grains in soil. Some of these microbial species precipitate gold from solution, Reith and others found.

Now another team reports how D. acidovorans performs its version of this trick: It secretes a protein snippet that snatches up dissolved gold, forming metallic gold. Nathan Magarvey of McMaster University in Canada and colleagues report the finding online February 3 in Nature Chemical Biology.

The bacterium’s gold-extracting technique is unusual, says geomicrobiologist Jim Fredrickson of Pacific Northwest National Laboratory in Richland, Wash. Dissolved gold is toxic to many bacteria, but passing electrons to the dissolved element converts it to its metallic, innocuous form. Another gold-altering microbe, Cupriavidus metallidurans, does the conversion inside its cells. The molecule that D. acidovorans secretes renders gold solid and inert.

“Somehow it’s sensing the gold and protecting itself,” says Fredrickson, who was not involved with the study.

Magarvey and his colleagues have named the secreted compound delftibactin. They found that delftibactin is similar to compounds that bacteria, fungi and some plants use to extract iron and other metals from solution. Perhaps as it was evolving, D. acidovorans co-opted the compound, enabling it to live in the company of gold, Magarvey says.

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