geosmins

Geosmin is an organic compound, specifically a bicyclic alcohol, that is responsible for the earthy scent produced by certain bacteria, most notably *Streptomyces*. This distinctive aroma is often associated with damp soil, particularly after rain, a phenomenon commonly referred to as petrichor. Geosmin is produced by actinobacteria, a phylum of Gram-positive bacteria, as a secondary metabolite. The compound is characterized by its low odor detection threshold, meaning it can be perceived by humans at very low concentrations.

The production of geosmin by *Streptomyces* is thought to serve a purpose related to spore dispersal. The earthy smell may attract soil-dwelling organisms, such as springtails, which then help to spread the bacterial spores to new environments. While geosmin is the primary contributor to the characteristic smell of soil, other volatile compounds can also play a role in its overall aroma profile. The detection of geosmin by humans is a fascinating example of how olfactory senses can be finely tuned to environmental cues. Its presence in water supplies, even at trace levels, can also lead to complaints about taste and odor due to its strong sensory impact.