Persistence of the Chromosome End Regions at Low Copy Number in Mutant Strains of Streptomyces rimosus and Streptomyces lividans

Dalia Denapaite1, Andrea Paravić Radičević1,2, Branka Čajavec1,3, Iain Hunter3, Daslav Hranueli2 and John Cullum1*

LB Genetik, University of Kaiserslautern, Postfach 3049, D-67653 Kaiserslautern, Germany

2PLIVA Inc., Research Division, Prilaz baruna Filipovića 25, HR-10 000 Zagreb, Croatia
3University of Strathclyde, Department of Pharmaceutical Sciences, 204 George Street, Glasgow G1 1XW, UK

Article history:

Received June 11, 2004
Accepted November 22, 2004

Key words:

linear chromosome, linear plasmid, deleted DNA, reversion, Streptomyces


Streptomycetes are important antibiotic producing bacteria that often exhibit genetic instability. One or both ends of the linear Streptomyces chromosome are lost spontaneously, resulting in viable mutant strains sometimes lacking hundreds of genes. We examined some strains of Streptomyces rimosus and Streptomyces lividans, which had been classified as »deletion mutants« and appeared to have lost chromosome end sequences. We discovered that the »deleted« sequences were still present in vegetative mycelium at a very low copy number so that they were normally not detected. The copy number in S. rimosus was estimated as 0.1–1.0  10–3/chromosome. Streptomyces spores contain the disappearing chromosome end sequences at a higher copy number than the vegetative mycelium, promoting their inheritance via spore preparations. This, in effect, represents a separation between germ line and deleted vegetative genomes, which has not been recognised before in Streptomyces, and has practical implications both for strain preservation and genetic studies.

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