Fungus Found in Australian Soil Can Oxidize Gold

The chemical process may make the metal more soluble and move it closer to the Earth’s surface.

May 24, 2019
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Fungi present in the soil of the so-called Golden Triangle Gold Prospect zone of Australia can oxidize the metal, researchers reported May 23 in Nature Communications. The reaction dissolves gold, after which the fungi precipitate the metal on their surfaces, a process that may help move the metal from deeper deposits in the Earth’s crust closer to the surface.

The result represents a previously unknown role for fungi in biogeochemical cycling, Saskia Bindschedler, a microbiologist from the University of Neuchatel in Switzerland who was not involved in the work, tells the ABC. “What I really like about this paper is that it shows that not only bacteria are able to oxidize inactive metals,” she says.

“Fungi are well-known for playing an essential role in the degradation and recycling of organic material, such as leaves and bark, as well as for the cycling of other metals, including aluminium, iron, manganese, and calcium,” coauthor Tsing Bohu of CSIRO tells the Australian Associated Press. “But gold is so chemically inactive that this interaction is both unusual and surprising—it had to be seen to be believed.”

Bohu and his colleagues sampled the surface soil of the region that was a gold “hot spot,” as they call it in their paper, and scanned for microbes that might be oxidizing the metal. That introduced them to an isolate of Fusarium oxysporum called TA_pink1. Experiments in the lab revealed that the fungal isolate could dissolve the metal, then precipitate nanoparticles of gold on its surface.

“There is an underlying biological benefit from this reaction,” Bohu tells the ABC. “We found gold-loving fungi can grow faster and bigger relative to other fungi that don’t work with gold.”