Microorganisms that are similar to fungi and simple bacteria. Actinomycetes are sometimes classified with fungi. They produce slender, branched filaments that develop into mycelium. Actinomycetes do not fix nitrogen from the air, but instead release ammonia from organic matter and reduce nitrites to nitrates. They are not fierce competitors and don’t develop well in the presence of high fertility, which can explain their scarcity during the initial stages of plant residue decomposition. Actinomycetes thrive in well aerated, neutral to alkaline soils. Streptomyces is the most populous of all actinomycetes and is the active ingredient in the product Actinovate which is used to treat soil diseases.
They are less active in acid or waterlogged soils but are extremely important to the decay of organic matter in dry regions. They are visible as the white, fungus-like threads on decaying organic matter. The earthy smell of newly plowed soil and the forest floor is compliments of actinomycetes. They are a higher form of bacteria and similar to fungi and molds. Actinomycetes are very important in the formation of humus. Actinomycetes may work near the surface or many feet below the ground. While decomposing animal and vegetable matter, actinomycetes liberate carbon, nitrogen, and ammonia, making mineral nutrients available for higher plants. Look for the white material on decaying matter in the compost pile.
Actinomycetes are said to be thread bacteria and are quite common in soil, especially in higher pH and drier soils. They commonly produce antibiotics on artifical media and give soil its characteristic "earthy" odor.