The ancient legend about the philosopher's stone of the alchemists, it turns out, has a very real, earthly and living embodiment. Only a very tiny one is the bacteria C. Metallidurans, which evolved to absorb toxic heavy metals, and gold and copper became their byproducts. In the form of nano-sized bars (called recycled gold).
The ability of C. Metallidurans to live in soil with a high concentration of heavy metals has always intrigued scientists. On the one hand, there are excellent living conditions: no competition, because in this environment everyone dies, and there is plenty of hydrogen to extract energy. These bacteria "feed" on copper, transforming it into a form that is very convenient for import from the soil into the body, but gold goes to it as ballast and this mixture is very poisonous. Why don't C. Metallidurans die?
Now scientists have found out: the metabolism of bacteria is based on a combination of the enzymes Cup A and Cop A. When the bacterium is hungry, the first is activated, it begins to absorb copper and by-product gold from the soil. When the bacterium is full, it activates the second enzyme and the copper again goes into an insoluble form, which is removed to the outside. Thus, C. Metallidurans is never oversaturated with toxins, and the precipitated gold forms nanometer-sized flakes or ingots.
Primary gold is a substance of geological origin, very ancient. Secondary is the products of processing minerals by various microorganisms that spread in different environments and have a small age. But scientists do not see the point in building a "golden farm" from colonies of C. Metallidurans, they are interested in the very mechanisms of transformation of substances, the understanding of which will optimize the processes of mining.