Gold dust found in the needles of Christmas trees

Money might not grow on trees, but it appears that gold does. Scientists have discovered tiny specks of the precious metal in the needles of Christmas trees.

A team in Finland found minuscule particles of gold in the needles of Norway spruce trees, a popular choice for Christmas decoration, collected by bacteria living within the plants themselves.

The research revealed that the spruce absorbs gold in liquid form directly from the soil, before the microorganisms transform it back into small solid chunks of the valuable element.

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This discovery was made by scientistsfrom the University of Oulu and the Geological Survey of Finland, who studied spruces growing above a known gold deposit in Santa's homeland, Finnish Lapland, near a satellite deposit of the Kittilä gold mine.

They utilised high-powered electron microscopy along with DNA sequencing to confirm both the presence of gold nanoparticles and several bacterial groups that appear more common where gold is present, reports the Daily Star.

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It is hoped that this could lead to the discovery of new gold deposits through a more environmentally-friendly mineral exploration method than simply starting to dig.

Dr Kaisa Lehosmaa, from the University of Oulu, said: "Our results suggest that bacteria and other microbes living inside plants may influence the accumulation of gold in trees. "This insight is useful, since screening for such bacteria in plant leaves may facilitate gold exploration.

"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."

The research team gathered 138 needle samples from 23 Norway spruce trees. One series of examinations utilised field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy to identify and verify gold particles; another sequenced the 16S rRNA gene to chart the needle-dwelling bacterial communities.

Gold nanoparticles were verified in four trees, frequently positioned alongside clusters of bacterial cells embedded in biofilm - the sticky, protective matrix that microbes construct.

DNA 'fingerprints' indicated specific bacterial groups more commonly linked with gold-positive needles. The researchers believe that microbe-produced biofilms subtly alter the chemistry within the needle, transforming dissolved, ionic gold into minute solid particles that the plant can safely store.

The fact that not every tree contained gold was expected, the scientists say, because individual trees access different water pathways and host distinct microbiomes that can differ from branch to branch. Needles containing higher gold concentrations showed reduced bacterial diversity overall, whilst particular 'indicator' groups emerged more frequently in gold-rich areas.

The study provides a microbial perspective on biogeochemical exploration, a method where vegetation is analysed to identify trace metals in underlying soil.

Research Professor Maarit Middleton, from the Geological Survey of Finland, said: "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."