Plasmids in different strains of Streptomyces ambofaciens: free and integrated form of plasmid pSAM2

Abstract

Five strains of Streptomyces ambofaciens were examined for their plasmid content. Among these strains, four belong to the same lineage (strains B) and the other was isolated independently (strain A). A large plasmid (ca. 80 kb), called pSAM1 in this paper and already described, was present in all B strains, and absent in strain A. A second plasmid, not described before, was found as covalently closed circular DNA in two of the four B strains. This plasmid with a size of 11.1 kb was called pSAM2. A restriction map for 14 enzymes was established. Hybridization experiments showed that a unique sequence homologous to this plasmid is integrated in a larger replicon, which is not pSAM1 and is probably the chromosome, in all B strains and not in strain A. It seems probable that the integrated sequence is the origin of the free plasmid found in two strains of the B family. It is noteworthy that the integrated form and the free plasmid may be found together. Transformation experiments proved that pSAM2 may be maintained autonomously in S. ambofaciens strain A and in S. lividans. pSAM2 is a self-transmissible plasmid, able to elicit the lethal zygosis reaction. pSAM2 was compared to the plasmids SLP1, pIJ110 and pIJ408, which all come from integrated sequences in three Streptomyces species and are found as autonomous plasmids after transfer to S. lividans. If pSAM2 resembles these plasmids in its origin, it does not appear to be related directly to them. Concerning their plasmid content, the two isolates of S. ambofaciens are very different.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization of the Bacterial Chromosome

“…Examples include the well-known integration and excision of the F plasmid in E. coli and integration of plasmid RP4 into many bacterial genomes such as Myxococcus spp. (169), pMEA100 in Nocardia mediterranei (223), pSAM in Streptomyces ambofaciens (267), and pSE101 in Saccharopolyspora erythraea and Streptomyces lividans (39). An especially striking example of this condition is manifest in interspecific crosses between Streptomyces spp.…”

Characterization of the Streptomyces lavendulae IMRU 3455 linear plasmid pSLV45

“…Actinomycetes contain additional extrachromosomal genetic elements including rolling circle replicating (RCR) plasmids such as pSAM2 and pIJ101 (Kendall & Cohen, 1988;Kieser et al, 1982;Pernodet et al, 1984). Actinomycete extrachromosomal elements have been shown to shuttle their own genes as well as chromosomal genes to other actinomycete hosts, providing a route for the exchange of genetic information (Bibb et al, 1981;Chen et al, 1993;Hopwood et al, 1985;Kinoshita-Iramina et al, 1997;Ravel et al, 2000).…”

“…All actinomycete chromosomes characterized to date are quite large, 8-9 Mb, and contain TIRs, TPs and internal origins of replication (Lezhava et al, 1995;Lin et al, 1993;Redenbach et al, 1999;Shiffman & Cohen, 1992). Therefore, actinomycete linear chromosomes and linear plasmids share similar features including TIRs, TPs and internal origins of replication.Actinomycetes contain additional extrachromosomal genetic elements including rolling circle replicating (RCR) plasmids such as pSAM2 and pIJ101 (Kendall & Cohen, 1988;Kieser et al, 1982;Pernodet et al, 1984). Actinomycete extrachromosomal elements have been shown to shuttle their own genes as well as chromosomal genes to other actinomycete hosts, providing a route for the exchange of genetic information (Bibb et al, 1981;Chen et al, 1993;Hopwood et al, 1985;Kinoshita-Iramina et al, 1997;Ravel et al, 2000).…”

Characterization of the attP site of the integrative element pSAM2 from Streptomyces ambofaciens

“…pSAM2 is an 11 kb element, originally isolated from Streptomyces ambofaciens, which produces the macrolide antibiotic spiramycin (Pernodet et al, 1984). pSAM2 can replicate, is self-transmissible, elicits the lethal zygosis reaction (pock formation) and mobilizes chromosomal markers (Smokvina et al, 1991).…”