Plants do more than photosynthesize – some of them make gold. In a boreal forest in northern Finland, scientists found tiny gold particles inside Norway spruce needles.
Plants like the Norway spruce host tiny microbial partners that tweak chemistry inside their leaves and needles in ways that science is only beginning to understand.
For the first time, scientists have linked bacteria living inside Norway spruce needles to the formation of gold nanoparticles.
“Our results suggest that bacteria and other microbes living inside plants may influence the accumulation of gold in trees,” says Postdoctoral Researcher Kaisa Lehosmaa from the University of Oulu, Finland.
The finding opens a path to greener gold exploration, and similar microbe-driven processes in mosses could help pull metals out of mining-impacted waters.
Do microbes in trees make gold?
The core question is straightforward: are microbes living inside spruce needles connected to the presence of gold nanoparticles? If yes, what does that mean for plants, microbes, and the way we search for minerals?
Geologists have long known that mineral deposits shed ions as rocks oxidize and bacteria get to work.
Those ions move into surface soils, where plants take up water and nutrients – metals included. With sensitive instruments, you can even detect those metals in plants or snow.
Researchers from the University of Oulu and the Geological Survey of Finland focused on trees growing above a known gold deposit in Finnish Lapland, at a satellite mineral deposit of the Kittilä gold mine.
That setting increases the odds that tiny amounts of gold travel through soil water into roots and up to the needles.
“Such biogeochemical methods have already been used in mineral exploration, but this new research enhances our understanding of what is actually happening in the process,” explains Research Professor Maarit Middleton from the Geological Survey of Finland (GTK).
Tree needles and gold particles
The team collected 138 needle samples from 23 Norway spruce trees and split them into two testing tracks.
One track searched for gold nanoparticles using field-emission scanning electron microscopy paired with energy-dispersive X-ray spectroscopy.
A bright, dense dot that matches gold’s X-ray signal counts as a confirmed particle. The other track sequenced a standard marker gene (16S rRNA) to map the bacteria living inside the needles.
In four trees, gold nanoparticles appeared inside the needles. Where gold appeared, the particles often sat next to clusters of bacterial cells embedded in biofilm – the protective, sticky coating that bacteria build to live in tight communities.
Microbial fingerprints
DNA sequencing of the biofilms pointed to specific bacterial groups linked with gold-containing needles. Taxa such as P3OB-42, Cutibacterium, and Corynebacterium were more common in needles with confirmed gold.
“This suggests that these specific spruce-associated bacteria can help transform soluble gold into solid particles inside the needles,” Dr. Lehosmaa says. “This insight is useful, since screening for such bacteria in plant leaves may facilitate gold exploration.”
How tree microbes make gold
Gold in the ground can move in a soluble, ionic form with water. Inside a needle, the microenvironments created by biofilms can change local chemistry – shifting conditions so that dissolved gold becomes less soluble and starts forming tiny particles.
Plants often isolate metals to keep essential processes running smoothly. Microbes benefit from the shelter of biofilms and may grab trace elements along the way.
“Our recent study provides preliminary evidence of how gold moves into plant shoots and how gold nanoparticles can form inside needles,” Dr. Lehosmaa explains.
“In the soil, gold is present in a soluble, liquid form. Carried by water, the gold moves into spruce needles. The tree’s microbes can then precipitate this soluble gold back into solid, nanosized particles.”
Deciphering the patterns
Not every tree contained gold nanoparticles, and that fact makes perfect sense. Trees tap different water pathways, and their microbiomes can vary even from branch to branch.
Needles with more gold tended to host fewer kinds of bacteria, but the overall communities didn’t split into two separate groups. Certain “indicator” groups were more common in the gold-touched environment.
The co-location of gold dots, bacterial cells, and biofilms suggests microbial involvement, but it isn’t a live-action view of a single bacterium reducing gold in real time.
The exact cause and effect of this process will need targeted experiments that track the transformation step by step.
Real world implications
Biogeochemical exploration already samples plants to look for what lies beneath. The new twist is the microbial angle inside leaves and needles.
If specific microbes correlate with gold particles, screening for those bacteria could sharpen plant-based surveys. That points to fewer blind drill holes, less disturbance, and better odds of finding the right targets.
The approach does not replace geophysics or traditional geochemistry. It adds another line of evidence. In regions where access is tight or environmental stakes are high, that extra signal could pay off.
The same biology that shapes metals inside needles could help pull metals from water. Aquatic plants and their microbes live on the front lines of metal exposure in streams near mines.
If biofilms and plant tissues nudge dissolved metals to form particles, that chemistry could be built into treatment systems.
“Metals can, for example, precipitate within moss tissues. Studying biomineralisation also allows us to explore how bacteria and microbes living in aquatic mosses could help remove metals from water,” Dr. Lehosmaa describes another ongoing study.
Gold inside trees – more answers needed
Plants are holobionts – teams made of the host plus its microbes. Those partners guide how nutrients and trace elements move, how stress is handled, and, in cases like this, how minerals form inside tissues.
In the Lapland spruces, microbes appear to help lock tiny bits of gold into safe, solid form. That tiny record inside a needle hints at the geology underfoot and at practical tools we can use on the surface.
Direct, time-resolved tests will be key. Show microbes taking soluble gold and forming nanoparticles under controlled conditions, and the case gets stronger.
New studies will need to expand beyond spruce and test other plants over different deposits and rock types.
Scientists will track seasons, map the groundwater routes, then tie microbial fingerprints to gold signals in a way that field crews can use.
That’s how science works – follow a clear path from careful observation to a reliable method.
In this case, that clear path runs through a place we’ve overlooked for too long: the small neighborhoods where plant cells and microbial biofilms set the rules for chemistry.
The full study was published in the journal Environmental Microbiome.
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