Plasmid DNA in the erythromycin producing microorganism, Streptomyces erythreus NRRL 2338

Streptomyces erythreus NRRL 2338, the erythromycin producing microorganism, contains extrachromosomal (plasmid) DNA. Four different plasmids, pSE1, pSE2, pSE4 and pSE6 present in the wild-type strain have characteristic mobilities on agarose gel electrophoresis, molecular weight and restriction endonuclease digestion patterns. Treatment of the wild-type strain with ethidium bromide or acridine orange gave two variants, one that could not convert erythronolide B to 3 (alpha)-mycarosylerythronolide B and another than produced 2 approximately 3 times more erythromycin A than the parental strain. Although the plasmid DNA profile of these two variants is different from the wild-type strain, it is not possible to conclude that any of the structural genes for erythromycin biosynthesis are located on the plasmids of S. erythreus NRRL 2338.