Have you ever noticed the special "earthy smell" after the first rain of a long summer?  Of course, rain itself doesn't have smell.  This special odor, also referred to as petrichor, actually comes from a bacteria called as actinomycete in soil. Actinomycetes create a byproduct called geosmin when soil is damp.The activities of actinomycetes in soil slow down during dry weather.  Actinomycetes create a byproduct called geosmin when soil is damp. The activities of actinomycetes in soil slow down during dry weather.  Actinomycetes are thread-like filaments bacteria that usually grow in warm and damp soil.  It has many other habitats including water environments or animal bodies;  However, soil is their main habitat.  After a long period of dry weather, the activities of actinomycetes in soil slow down.  Just before the rain, as the soils become damp, actinomycetes start to wake up and create a byproduct called geosmin which contributes to the "earthy smell."

Actinomycetes are important to keep a sustainable soil environment.  Actinomycetes play an important role in soils by improving the soil nutrients and promoting the growth of plants.  They can decompose dead animals and plants, then re-make nutrients for plant growth.  Moreover, they can also work together to control the growth of harmful soil bacteria to keep a sustainable soil environment.