The oxytetracycline-producing Streptomyces rimosus strains R6-65 and R7 (ATCC 10970) are lysogenic for the two narrow-host-range phages RP2 and RP3. Both phages are released at low frequency from the lysogenic strains and form plaques on 'cured' S. rimosus strains. RP2 and RP3 are of similar shape with flexible tails and contain double-stranded DNA of about 70 % G + C with cohesive ends (group B1 of bacteriophage classification). The two phages also have identical, very slow, growth kinetics in S. rimosus, with a latent phase of about 6 h and a rise period of about 4 h. RP2 and RP3 are heteroimmune and they differ slightly in their size of phage particles and length of DNA (647 and 62.4 kb for RP2 and RP3, respectively). The restriction maps of the two phages are completely different, and hybridization experiments showed only one short region of sequence similarity (less than 430 bp); the two phages are thus essentially unrelated. Both phages lysogenize their hosts by recombination via defined attachment (aft) sites. The positions of the attP sites have been localized on the restriction maps of RP2 and RP3 to restriction fragments of 800 and 300 bp, respectively. The prophages did not affect the level of oxytetracycline production or the genetic instability of this trait. IntroductionStreptomyces rimosus produces the commercially important antibiotic oxytetracycline. It is the genetically best-characterized species among industrially important Streptomyces. Chromosomal genetic maps have been constructed for three strains: M4018, R7 (ATCC 10970) and R6 (Friend & Hopwood, 1971; AlaEevi6 et al., 1973). Classical genetical methods have also been applied to analyse the genetics of oxytetracycline biosynthesis in strains R6 and M4018 (Pigac & Alakvi6, 1979;Rhodes et al., 1981). In addition, genes for oxytetracycline production and resistance have been cloned and analysed from derivatives of strain M4018 Binnie et al., 1989). S. rimosus strain R6 proved to be genetically unstable, and in this strain the oxytetracycline production and resistance genes are localized at an unstable region of the chromosome (Cullum et al., 1991 ;Gravius et al., 1993). S. rimosus strains R6, R7 and M40 18 contain three related giant linear plasmids, between 280 and 370 kb in size (Cullum et al., 1991 For more than 50 years it has been known that actinophages can attack streptomycetes, but they did not attract much attention until their undesirable interference with industrial fermentations was recognized (Welsch, 1969). More recently, however, considerable advances have been made in the genetic and physical analysis of phages and their interaction with their hosts (Lomovskaya et al., 1980). Streptomyces phages have also been developed as DNA cloning vectors (Chater, 1986).Interest in S. rimosus phages also arose because of problems during industrial fermentations. Ya. I. Rautenstein and collaborators (Rautenstein et al., 1972) reported several cases of lysis of S. rimosus cultures of two lysogenic strains (560 and IK) under industrial co...
The sequence of the cohesive ends of actinophage RP3 DNA has been determined. As with all other phages of Gram-positive bacteria that have been studied sofar, RP3 DNA has 3'-protruding ends. A shuttle cosmid has been constructed containing this cos area which can be efficiently transduced by phage RP3 to host cells of Streptomyces rimosus.
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