The Streptomyces aureofaciens plasmid pIMB R8 and its use for shuttle vector construction

pSRD191, a new member of RepL replicating plasmid family from Selenomonas ruminantium

A numerous plasmid population was detected in strain 19 of Selenomonas ruminantium. The population was found to consist of six plasmids in size ranging from 1.4 to more than 20kb. The smallest 1.4kb cryptic plasmid pSRD191 was further characterized. Sequence analysis identified a single ORF encoding the 177-residue putative replication protein (Rep191) which shared significant homology with RepL family of replication protein from Firmicutes (staphylococci and bacilli). PCR analysis and Southern hybridisation showed that pSRD191 related plasmids are frequently encountered in rumen selenomonads.

Highly transformable mutants of Streptomyces aureofaciens containing restriction-modification systems

Streptomyces aureofaciens 13 is a mutant defective in chlortetracycline production. It was chosen as a potentially useful host for gene cloning in investigations of the organization of the biosynthetic genes for the tetracycline antibiotic pathway. From the Streptomyces aureofaciens 13 strain, three suitable clones were used for our work. The conditions for optimal formation and efficient transformation of protoplasts with plasmid DNAs have been determined. Transformation frequencies of about 10(4) to 10(5) per microgram of plasmid DNA were obtained when plasmids were isolated from Streptomyces strains. From the patterns of restriction enzyme digestion of plasmid DNA isolated from Streptomyces aureofaciens transformants, it was observed that the clones express modification systems which render plasmid DNAs resistant to cleavage by HindIII and EcoRI. Additionally, one of the clones produces the restriction endonuclease Sau13I (isoschizomer of SauI). The presence of the restriction-modification system of Sau13I does not reduce the efficiency of plasmid transformation.