It turns out that not only to us, people, the aroma of damp earth and recent rain seems attractive. This smell, which bears its own name petrikor, comes from the organic compound geosmin, produced by microbes - including Streptomyces bacteria. It is known that streptomycetes release this substance when they die, and that different creatures, including humans, have a special reaction to it. The question is, why is this happening?
To understand the role of geosmin in the soil environment where bacteria live, an international team of researchers wondered if the odor of streptomycetes attracts soil-dwelling arthropods. Their guesses were confirmed when scientists discovered colonies of springtails (Collembola), tiny arthropods that live in organic environments, in a network of field traps with bait from Streptomyces coelicolor. Then the team carried out a series of experiments already in the laboratory. And it turned out that these kids are big fans of geosmin. And streptomycetes play the role of food for them.
What is beneficial for bacteria to be eaten by arthropods? Streptomyces is similar in many ways to a filamentous fungus. When ready to reproduce, it creates spores that can spread newborn bacteria. Only now, in order to spread, you need a carrier, and this mission falls on the springtail. They feed on streptomycete colonies and spread their spores through fecal pellets and transport on their hydrophobic bodies.
The conclusion is simple: the production of geosmin by bacteria is an integral part of the process of their sporulation. This is the completion of the life cycle through the attraction of soil arthropods, which will spread the spores so that everything starts anew.
So the next time you smell the rain, you can remember that this pleasant scent is a sign of a whole circle of life that passes very close to us.