Is the colour of the mature aerial mycelium (spore mass) of streptomycetes a diagnostic key-character of decisive taxonomic importance?

A white sporulated stable mutant strain (strain No. 66/m) of a Streptomyces sp. belonging to the nigrescens group of the typical grey Streptomyces spp. has been isolated. On the basis of ISP *International Streptomyces Project) criteria strain No. 66/m would be considered a true member of the albus-group of Streptomyces (regarded by some workers as a well separated assemblage of species) all the more so because it fits into this alien group at least in such a degree as into that from which it has originated. Caution is necessary in using the aerial mycelium colour as a distinguishing diagnostic property for establishing large intraspecific groups, series, or even in separating species of Streptomyces.