摘要：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.
关键词：linear chromosome; linear plasmid; deleted DNA; reversion; Streptomyces
