Relationships of the Actinomycetales

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Abstract
The evolutionary scheme herein proposed involves a series of organisms showing morphological and physiological relationships beginning with a sporangial ancestor with motile spores evolving to reduced spore production and nonmotile spores. This scheme seems best to fit the facts as they exist today. Although related both to fungi and to bacteria, especially the propionic bacteria, the actinomycetes would appear to be a separate phylogenetic line. Whether this theory is acceptable or not will await many more comparative studies of morphology, physiology and chemistry. From a practical standpoint we are certain, however, that actinomycetes must be isolated, grown and studied more as if they were fungi than bacteria. This is because: (1) Spores and spore germination are like those of fungi. (2) Vegetative growth in surface and submerged culture is fungus-like. (3) Mycological characteristics used in identification seem most fundamental. (4) Methods required for maintaining vigorous and stable cultures are like those used for fungi. (5) The colony and its mode of growth are more fungus-like than bacterial.