Actinomycetes form a special order within the bacteria: thread-like structures, resembling hyphae (fungal threads). However, they are not fungi, as they do not contain a cell nucleus, nor does their cell wall contain cellulose or chitin, in contrast to the cell wall of fungi.
Some species of actinomycetes, such as Streptomyces sp., can secrete antibiotics and are thus of great importance to soil health. The presence of these actinomycetes contributes to an important form of specific disease resistance that can be used to suppress certain pathogenic soil fungi. Other actinomycetes are direct parasites of living fungal filaments and resting spores. They can also compete with pathogenic fungi for nutrients. A group of actinomycetes can also break down difficult to digest organic material such as cellulose, lignin and chitin. In doing so, they play an important role in the formation of stable humus, which can be used to improve soil structure, CEC and water balance. Actinomycetes cannot tolerate acidic conditions well, with the most favorable pH values being between 6.5 and 8.0.