As we use more and more chemicals in perfumes, insect repellents, and odor neutralizers, pheromones no longer work, and our noses are also getting weaker, and we may need more and more intense scents to detect them.
But there are still natural smells that we can miraculously detect, like the smell of earth after rain. For the first time, we have identified the receptor that detects the smell of rain in our noses: a compound called geosmin.
Geosmin is a terpene molecule that has a strong odor even in very small concentrations. OverflowingIf it only made up 5 parts per billion of the air, we could still detect it. But not just us, but also the bacteria-hunting worms, which see it as a warning sign.
The small world of bacteria and worms
The compound is produced by soil bacteria and consumed by small worms, such as Certain types are elegant. Nematodes are really elegant, with their slender bodies and 1 mm long. But many bacteria produce substances that are toxic to the worms, and if the bacteria that produce the toxins also produce geosmin, the worms can sense it, even before they eat the microbe.
When the worms were also able to encounter the bacteria, they avoided it by sensing geosmin. But in one experiment, worms genetically deprived of their sensory organs were tested and found to be unable to detect geosmin and to eat the toxic bacteria.
Geosmin, produced by soil microorganisms, not only appears in the soil after rain, but can also be found in various plants. For example, in the flowers of cacti and beets. Geosmin, a chemical signal that alerts muslins to spoiled food, for example, attracts camels to wetlands. But if it works this way in animals, it should work in humans as well. In the case of fish, beans, cocoa, water, wine and grapes, geosmin signals deterioration and warns of food unsuitability, says Stephanie Frank, a food chemist at the Leibniz Institute.
Amazingly developed sense of smell
Surprisingly, we can detect the smell of geosmin even in very small concentrations, for example in water. According to researchers at the Leibniz Institute, if you put a teaspoon of geosmin in 200 Olympic-sized swimming pools of water, you would still detect it.
But how do we still have that hound nose?
The compound’s existence has been known since 1965, but how it is perceived has remained a mystery until now. Dietmar Krautwurst, a researcher at the Technical University of Munich, led the team that discovered the receptor for the smell of damp earth in our nose. The researchers began examining the receptors and succeeded in identifying and describing the appropriate receptor. Of the 616 human olfactory receptor variants tested, only one, the OR11A1 receptor, responded to geosmin at relevant concentrations. But the researchers also investigated whether the receptor responded to other intense food odors.
Of the 177 substances tested, only the earthy odorant (also of microbial origin) 2-ethylphenol could activate the receptor.
The research is important not only because it highlights the biological importance of the compound, but it may also lead to the development of new detection systems. With these elements, we can check the quality of food during production and storage, or check the quality of freshwater reservoirs.
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