ACTINOMYCETES, is the common name for an order of organisms that are transitional forms between true bacteria and mold fungi. They are characterized by elongated filamentous cells, or hyphae, 0.5 to 0.8 microns in diameter. The hyphae spiral and branch to form a true mycelium (a mass of interwoven filaments) on solid culture mediums; they may also segment to form rodshaped bodies that are morphologically indistinguishable from bacteria. Most actinomycetes contain pigments.
Actinomycetes can grow on all types of natural substrates in a temperature range of 68° to 86° F (20° to 30° C). Most of the members of the order are aerobic (requiring oxygen), but some pathogenic forms are either nonaerobic or grow best at a low oxygen pressure. They reproduce by spores or fission.
Actinomycetes are important because they bring about the decomposition of plant and animal residues and liberate carbon and nitrogen for plant growth. They also inhibit the growth of other bacteria and fungi and thus serve as a source for most antibiotics. Two known diseases —actinomycosis, which affects cattle, and narcodosis, which affects humans—are caused by actinomycetes.
Actinomycetes belong to the order Actinomycetales, class Schizomycetes