Actinomycetes are long, branched filamentous bacteria. The most striking property of Actinomycetes is fungal-type morphology. Although Actinomycetes were looked upon initially as fungi, later research revealed that Actinomycetes were filamentous, branching bacteria. Masses of these filaments are called mycelia, and a singular mass is called mycelium. The Actinomycetes are represented most commonly by saprophytic forms that have an extensive impact on the environment by decomposing and transforming a wide variety of complex organic residues. Actinomycetes are widely distributed in nature, in freshwater, seawater, cold- and warm-blooded animals, and compost. Actinomycetes are responsible for the earthy musty odors that affect the quality and public acceptance of municipal water supplies in many parts of the world. The best known genus of Actinomycetes is Streptomyces. Streptomyces are one of the bacteria that are most commonly isolated from soil and are also considered to be significant in water supply problems.