[Multiplication of a DNA fragment in Streptomyces antibioticus--producer of oleandomycin].

Two strains of Str. antibioticus producing oleandomycin were studied. Strain 326 was obtained from the initial laboratory strain and strain 1607 from strain 326 as a result of multistage selection aimed at increasing the antibiotic production capacity. Extrachromosomal ring DNA could be identified in strain 1607. The identified DNA was designated as eSA1 or extrachromosomal element of Streptomyces antibioticus 1. The molecular weight of this DNA is 21.3 Md. It is represented by 1 copy per chromosome. No eSA1 was isolated from strain 326 at CsCl-EtBr gradient. Hybridization studies according to Southern with the use as a probe of 32-eSA1 DNA showed that strain 326 contained 1 copy of eSA1 per chromosome in the integrated state. The hybridization studies, electron microscopy and analysis of the total DNA in CsC1-EtBr gradient showed that eSA1 in strain 1607 was tandemly multireplicated in the chromosome content. In the autonomous state its number was approximately equal to 1 copy per chromosome. The presence of eSA1 in strain 1607 in the autonomous state probably results from its segregation during homologous recombination due to tandem multireplication. The data are indicative of multiplication in strain 1607 of the chromosome fragment 23.3 Md in size. It is suggested that an increase in the oleandomycin production capacity of strain 1607 is associated with multiplication of the DNA fragment (eSA1) containing the genes determining production of the antibiotic.