Chemists have often pondered why the germ Delftia acidovorans is frequently found on the surface of tiny gold nuggets.
Its presence led scientists to speculate it may be creating the particles from soluble gold — ions of gold that are dissolved in water.
But the puzzle was how D. acidovorans did this trick, as soluble gold is toxic.
The answer, suggest researchers in Canada, lies in a molecule excreted by the microbe that both shields the organism and transforms the poisonous ions into particles.
"This finding is the first demonstration that a secreted metabolite can protect against toxic gold and cause gold biomineralisation," the process by which living organisms produce minerals, they wrote in the journal Nature Chemical Biology.
The molecule, delftibactin A, is capable of achieving this feat within seconds in pH-neutral conditions at room temperature.
Study co-author Nathan Magarvey of Ontario's McMaster University told
But such processes seem "distinctly possible," he said in an email exchange.
Previous research had shown that another bacterium found on gold, Ischiadicus metallidurans, deals with toxicity by storing the ions inside its cells.
Soluble gold, invisible in a glass of water, is found in the ocean, groundwater and other natural water sources.
Solid gold is mainly formed through geological processes in large veins underground.
Magarvey said the study may implicate D. acidovorans in secondary deposits such as nuggets found in rivers.
The bacterium, he added, is not found only on gold but also in the soil and in water. Still unclear, though, is what the organism feeds on.