Genetic determinants of active antibiotic-producing soil streptomycetes

Plasmids or covalently closed circular (CCC)-DNA molecules are abundant in the genus Streptomyces, and have been suggested to be involved in the genet ic control of the production of many antibiotics in these organisms. In thi s study, 21 active antibiotic-producing Streptomyces isolates were screened for their plasmid content by an alkaline lysis method which revealed the p resence of a small plasmid DNA in the positive control Streptomyces lividan s ATCC 35287, containing pIJ702 plasmid (5.65 kb in size). However, no low molecular weight plasmids were observed in the tested antibiotic-producing Streptomyces strains suggesting that antibiotic production in these strains is likely chromosomally encoded DNA. Treatment of 2 Streptomyces strains w ith 10 mM ethidium bromide (EB) resulted in the failure to produce aerial m ycelia and antibiotic activity.