Unbelievable but True: This Tree Secretly Hides Gold in Its Thorns!

Environmental Microbiome, this study highlights a previously poorly documented biological process, called biomineralization, during which microorganisms participate in the formation of minerals inside living tissues. This discovery could improve gold prospecting while opening prospects for the natural decontamination of environments affected by mining extraction.

A formation of gold nanoparticles at the heart of the needles

Researchers have therefore demonstrated, for the first time, the presence of gold nanoparticles in the needles of the Norway spruce. These particles, with a size of the order of a nanometer (a millionth of a millimeter), are completely invisible to the naked eye. They form directly inside the needles, in the area where the plant captures light to produce its energy. There, they are sometimes stuck in the substance surrounding the cells. The process by which they appear is called biomineralization, that is, the controlled precipitation of inorganic substances by living beings.

Unlike the passive accumulation of metals found in some indicator plants, here gold is not simply absorbed in soluble form. He finds himself transformed. Scanning electron microscopy (FE-SEM) analysis coupled with energy dispersive spectroscopy (EDS) confirmed the presence of solid gold in the needles of four out of twenty-three trees sampled at a satellite site of the Kittilä gold mine, Finland. Gold concentrations ranged from 0.2 to 2.8 µg/kg dry weight.

This precipitation is not constant. Three of the four needles containing nanoparticles, however, displayed gold contents below the detection threshold. This shows that the formation of nanoparticles is not strictly linked to the total concentration of gold in the needle, but probably to other biological factors yet to be elucidated. The results suggest a localized, irregular process conditioned by the internal microecology of the tree.

An active role of endophytic bacteria in gold precipitation

The most significant discovery of the study is based on the involvement of endophytic bacteria. In other words, microorganisms living inside plant tissues without causing disease. Certainly these bacteria are naturally present in plants. But their role in biomineralization remained hypothetical until now. Here, their direct intervention in the transformation of soluble gold into solid particles was precisely demonstrated.

The researchers used 16S rRNA amplicon sequencing, a genetic analysis method targeting bacteria found in the needles. Of the 138 samples, they identified more than 998 bacterial genera, with phyla dominating Pseudomonadota, Bacillota And Actinomycetota. What distinguishes needles containing nanoparticles is not the overall diversity of bacterial communities, but the increased presence of certain specific genera.

Among the most notable: P3OB-42, Cutibacterium And Corynebacterium. These taxa were detected more frequently and significantly in needles containing gold in the form of nanoparticles. They appear encapsulated in biofilms, viscous matrices of polysaccharides and proteins which allow bacteria to settle permanently in tissues. These biofilms are systematically present around the gold particles detected by microscopy. They reinforce the hypothesis of their direct involvement in the precipitation of the metal.

The presence of these biofilms, associated with these bacterial genera, suggests a precise biochemical activity. Bacteria could reduce gold ions to elemental gold via specific enzymes or metabolites. This active, and not passive, mechanism gives microbes a catalytic role in the formation of metal particles.

An impact on bacterial diversity and a detectable biological signature

The results show that needles containing gold nanoparticles harbor lower bacterial richness. Nevertheless, the overall composition of endophytic communities remains similar between gold-bearing and non-gold-bearing trees. This reduction in microbial biodiversity in the presence of heavy metals is consistent with observations made on other plants exposed to metalliferous environments.

To better understand the links between certain bacteria and the presence of gold, Kaisa Lehosmaa's team compared the microbes present in the needles, depending on whether or not they contain gold nanoparticles. To do this, they used statistical tools and computer models capable of analyzing large quantities of data. These analyzes identified three types of bacteria – P3OB-42, Cutibacterium and Corynebacterium. They are much more common in needles containing gold.

Towards ecological mining exploration and decontamination applications

The practical implications of these discoveries go far beyond simple scientific curiosity. By identifying a causal relationship between bacteria, gold and plants, researchers are paving the way for bio-inspired mining prospecting methods, based on the analysis of the plant microbiome. The notion of a “gold microbial signature” is therefore taking shape. Certain bacteria could betray the presence of gold by their specific metabolic activity. This approach could replace or complement traditional techniques, which are often costly, invasive and have a high environmental impact.

In this context, trees like spruce become real integrated biological sensors. By studying their internal bacteria, it would be possible to detect the presence of a deep gold deposit without digging. This method could be applied to other plant species, in other geological contexts, with comparable efficiency, provided that the relevant bacteria-metal associations are identified.

At the same time, the study suggests applications in phytoremediation. Particularly in aquatic environments polluted by heavy metals from mining activity. Kaisa Lehosmaa raises the possibility of using certain aquatic mosses, also colonized by precipitating bacteria, to extract toxic metals from contaminated water.

This type of approach, at the crossroads of microbial ecology and geochemistry, is part of a logic of sustainable development. It makes it possible to combine technological efficiency and respect for ecosystems, by mobilizing natural interactions already present in the environment.

Finally, the economic and environmental potential remains real. But the commercial exploitation of these nanoparticles remains excluded. They are far too small to be collected. Their value lies solely in their function as a natural tracer, and in what they reveal of underground dynamics invisible to the naked eye, but essential for the geology of tomorrow.

Source: Kaisa Lehosmaa et al., “Biomineralized gold nanoparticles along with endophytic bacterial taxa in needles of Norway spruce (Picea abies)”. Environmental Microbiome (2025)