APPLETON, Wis. — In a discovery that blends botany with metallurgy, scientists have uncovered a remarkable process where ordinary trees are essentially mining gold from the soil, thanks to microscopic helpers living within their tissues. Researchers from the University of Adelaide in Australia have detailed how hidden microbes inside eucalyptus trees convert dissolved gold ions into solid metal particles, a phenomenon that could one day revolutionize sustainable mining practices.
The findings, published in the journal Nature Communications earlier this month, stem from fieldwork conducted in the gold-rich Kallara region of Western Australia. There, eucalyptus trees — known locally as gum trees — were found to contain up to 80 parts per billion of gold in their leaves, far exceeding typical soil concentrations. Lead researcher Dr. Chris Reid, a biogeochemist at the university, explained the mechanism during a press briefing in Adelaide on October 15.
"These trees are acting like natural prospectors," Dr. Reid said. "The microbes inside them, particularly bacteria from the Cupriavidus genus, are reducing toxic gold ions absorbed from the groundwater into stable nanoparticles. It's a survival strategy for the plant, detoxifying the soil while concentrating the metal."
According to the study, the process begins when tree roots uptake water laced with gold chloride complexes from mineralized underground deposits. As the water travels up through the xylem, symbiotic microbes in the leaves interact with these ions. Using enzymes, the bacteria strip away chloride and reduce the gold from its soluble Au(III) state to inert Au(0) metal, forming particles as small as 20 nanometers in diameter.
This isn't entirely new territory for science. Phytomining, the idea of using plants to extract metals, has been explored since the 1990s, but the role of endophytic microbes — those living inside plant tissues without causing harm — adds a crucial layer. Earlier research in 2013 by the same team identified gold in eucalyptus leaves, but the microbial involvement was only hypothesized until now. Advanced techniques like synchrotron X-ray analysis at the Australian Synchrotron facility confirmed the nanoparticles' presence and composition.
Dr. Reid's team collected leaf samples from 20 eucalyptus trees across a 10-square-kilometer site near Kalgoorlie, a historic gold rush town. The analysis revealed gold concentrations varying from 8 to 60 parts per billion, with higher levels in trees closer to known ore bodies up to 30 meters below the surface. "The trees are essentially sampling the subsurface geology," Dr. Reid noted. "Miners could use leaf chemistry to pinpoint deposits without invasive drilling."
While the Australian discovery has garnered international attention, similar processes have been observed elsewhere. In New Zealand, scientists at Massey University reported in 2018 that certain ferns accumulate gold via microbial assistance, though at lower yields. A 2020 study from the University of São Paulo in Brazil suggested Amazonian trees might do the same with nickel and cobalt, but gold-specific cases remain rare.
Not all experts are convinced of the scalability. Dr. Melissa Anderson, a mining engineer at Colorado School of Mines, who reviewed the paper, cautioned that while intriguing, the gold yields are minuscule. "A single tree might yield just micrograms of gold after incineration," she said in an email to The Appleton Times. "To make it economically viable, you'd need vast plantations on mineralized land, and energy costs for processing could outweigh benefits."
Environmental advocates, however, see promise. The process offers a greener alternative to traditional mining, which often involves cyanide leaching and habitat destruction. According to a report from the World Wildlife Fund released last year, conventional gold mining contributes to 20% of global mercury pollution. Phytomining with microbes could reduce that footprint, especially in developing regions.
In Australia, where gold production hit 314 tons in 2023 according to the Australian Bureau of Statistics, the government is funding pilot projects. The Minerals Council of Australia announced a $2 million grant on October 20 to test eucalyptus-based extraction in the Pilbara region. "This could extend the life of aging mines," said council CEO Warren Pearce. "It's bio-prospecting at its finest."
Back in the lab, Dr. Reid's team is engineering the microbes for enhanced efficiency. By genetically modifying the Cupriavidus bacteria to overexpress reductase enzymes, they've boosted gold reduction rates by 40% in greenhouse trials. Field applications are years away, but collaborations with biotech firm Rio Tinto aim to accelerate commercialization.
The discovery also sheds light on ancient ecosystems. Geologists speculate that similar microbial-plant partnerships may have concentrated gold deposits over millions of years, influencing where humans later found nuggets during gold rushes like California's in 1849 or Australia's in 1851. "Nature has been doing this alchemy longer than we've been digging," Dr. Reid quipped.
Critics point to potential ecological risks. Introducing engineered microbes could disrupt soil microbiomes, according to a cautionary note in the journal Environmental Science & Technology. Dr. Elena Vasquez, an ecologist at the University of Wisconsin-Madison, emphasized the need for long-term studies. "We don't want to trade one environmental problem for another," she said.
As research progresses, the "gold-growing trees" could symbolize a shift toward bio-inspired technologies. From cancer-fighting gold nanoparticles to sustainable electronics, the implications extend beyond mining. In Appleton, local botanists at the University of Wisconsin-Fox Valley are already discussing trials with hardy Midwest species like willows, which share eucalyptus' water-transport traits.
Whether this leads to forests of fortune or remains a scientific curiosity, the work underscores the hidden complexities of plant life. As Dr. Reid put it, "Plants aren't just green; they're geochemical wizards, and their microbial partners are the real MVPs." For now, the trees stand sentinel in the outback, quietly turning earth into treasure.