If you’ve wondered why the ground, or the road smells a bit odd when it rains after a long dry spell, wonder no more… The smell is given off by Streptomyces bacteria, a genus belonging to the Actinomycetales order of Gram-positive eubacteria, also called actinomycetes.
The bacteria grow in damp, warm earth before fine weather dries out the soil, which then blows around as dust. During a dry spell, actinomycetes produce spores that are released on contact with moisture. Rain hitting the ground kicks up an aerosol of water and soil and you breathe in fine particles of soil containing the bacteria.
Cool! via yak.net.