Selective isolation of members of the Streptomyces violaceoruber clade from soil.

Large numbers of filamentous actinomycetes which formed distinctive red coloured colonies were isolated from three out of four composite soil samples using a medium designed to be selective for members of the Streptomyces violaceoruber clade, a taxon which includes the model organisms "Streptomyces coelicolor" A3(2) and "Streptomyces lividans" 66. The isolation medium, dextran-histidine-sodium chloride-mineral salts agar supplemented with antibacterial and antifungal antibiotics, also supported the growth of representatives of the S. violaceoruber clade. One hundred and ninety one representatives of the isolates that produced red colour colonies on the isolation medium were distributed into four colour groups based on their ability to form distinctive pigments and morphological properties typical of members of the S. violaceoruber clade, an assignment that was confirmed by corresponding 16S rRNA gene sequencing studies. The selective isolation and characterisation procedures used in the present investigation provide a practical means of determining the taxonomic diversity, geographical distribution and roles of representatives of the S. violaceoruber clade in natural habitats.