Sources and dispersion of microorganisms in the atmosphere

The basic sources of airborne microorganisms comprise soil, plants, waste-water, man and animals, and some industrial processes based on growth and activities of microorganisms. Aerosols, produced by wastewater treatment processes, represent a real health risk. 

Many microorganisms, including viruses, bacteria, protozoa, yeasts and algae, lack active dispersal mechanism. They rely on external mechanical forces for their liberation into the atmosphere. 

Myxomycetes are adapted to wind dispersal. Some merely expose a dry, powdery mass of spores above the substratum. Others expose small, dry spore masses on stalks. A few species are splash-dispersed or possess an active discharge mechanism. 

Filamentous fungi are well adapted for the aerial transmission of spores. The discharge can be passive or active. Passive mechanisms have been classified as follows [3]  

Active mechanisms for spore liberation are known in many Phycomycetes, Ascomycetes, Deuteromycetes and Basidiomycetes. Some Phycomycetes have various discharge mechanisms for ejecting spores into the air. Some Ascomycetes have explosive asci, which typically swell at maturity and finally burst at the tip, propelling the spores into the air. In Basidiomycetes, the basidium produces one or more sterigmata, at the end of each of which, one basidiospore is formed. When the spore is mature, a drop of liquid is excreted at the hilum end of the spore and almost immediately the spore moves off. 

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