Explainer: How bacteria give the rain its unique smell

A genus of bacteria called streptomyces uses the fragrance to entice arthropods for spreading their spores.


NSFW    NORFOLK, UNITED KINGDOM — New research may explain why rainfall on the soil creates a unique scent in the air. According to the study published in Nature, the smell of rain is caused by geosmin, a chemical secreted by a genus of soil-dwelling bacteria called streptomyces.

Writing a news release from John Innes Centre, researchers say the scent is bait for springtails, tiny 1.5mm-long arthropods.

The tiny six-legged animals sport antennas to detect geosmin. As springtails are attracted to the substance, they follow the scent and eat the bacteria.

By encouraging springtails to eat them, streptomyces get their spores on the arthropods and in their feces, which allows the bacteria to spread and reproduce. This mutually beneficial relationship may have endured for 450 million years.

Streptomyces produce antibiotics that kill nematodes and fruit flies, but not springtails. According to the scientists, this is evidence that springtails have evolved to privilege the bacteria as a food source, which the springtails help to spread.
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