Scientists discover gold nanoparticles hidden in spruce tree needles

Christmas tree farm. — Scientists found gold nanoparticles in four of the 23 spruce trees sampled in the study. (Image credit: Douglas Sacha/Getty Images)

When Burl Ives sang "Silver and gold decorations, on every Christmas tree" in "Rudolph the Red-nosed Reindeer," he surely didn't know that Christmas trees actually have gold inside their needles — but that's exactly what new research has found.

A study published Aug. 28 in the journal Environmental Microbiome reports that Norway spruce trees (Picea abies) concentrate gold nanoparticles with the help of their resident bacteria.

These resident bacteria are known as endophytes — symbiotic microorganisms that facilitate hormone production and nutrient absorption, among other functions. In the spruce trees, these bacteria segregate soluble gold particles that the trees take up in water through their roots.

The process is a form of biomineralization, in which living things control the formation of minerals in their tissues through a wide array of processes. In this case, the endophytes likely concentrated the particles to reduce their toxicity.

Striking gold

For the study, the researchers investigated spruce trees near the Kittilä mine in northern Finland — the largest producer of gold in Europe. The researchers examined 138 needle samples from 23 spruce trees. Needles from four of the trees contained gold nanoparticles.

The nanoparticles were surrounded by biofilms created by bacterial genera such as P3OB-42, Cutibacterium and Corynebacterium. These films are polysaccharide (complex sugars) and protein compounds secreted by the bacteria that allow them to persist within the plant tissues.