Today I Learned: The “After It has Rained Outside” Smell is Partly Produced By a Bacteria

Source: Actinomyces israelii

So we are all familiar with the awesome smell outside after a rain storm right (maybe you don’t like it, but I sure do, smells like nature!)? Well today I learned that smell is actually produced by a bacteria from the phylum Actinobacteria. These bacteria live in many places (including potentially on and in you) however they are predominantly found in the soil where they assist in the decomposition of organic matter (like dead plants), and help convert them into forms that can be used by new plants, which is a function normally performed by fungi. In addition to acting like fungi, this bacterial class also grows in colonies that LOOK like fungi too, forming what is known as mycelium.

Source: Fungal Mycelium

Anyway back to the rain smell! These bacteria produce a compound called geosmin, which is an organic compound with a “distinct earthy flavor and aroma.” When it rains, this compound is kicked up into the air from the soil. The human nose is able to detect it at concentrations down to 5 parts per trillion. Compare this to the ability of a shark to detect blood in water (1 part per million) and you start to realize just how sensitive our noses are to this Geosmin!

Source: Geosmin

So next time you go outside after it has freshly rained and smell that familiar sent, you can thank these Actinomyces for doing their job breaking down dead plant matter and making Geosmin for you to smell.

Sources:
https://en.wikipedia.org/wiki/Actinobacteria
https://en.wikipedia.org/wiki/Actinomycetales
http://www.compoundchem.com/2014/05/14/thesmellofrain/
https://en.wikipedia.org/wiki/Geosmin
http://www.smithsonianmag.com/science-nature/what-m