Streptomyces lipmanii expresses two restriction systems that inhibit plasmid transformation and bacteriophage plaque formation

The importance of homologous recombination in the generation of large deletions in hybrid plasmids in Amycolatopsis mediterranei

The cloning vector pRL60 was developed previously as a tool for genetic manipulations in Amycolatopsis mediterranei, which produces the commercially and medicinally important antibiotic rifamycin. Here, a method based on intraplasmid recombinations is described for the construction of smaller plasmids in A. mediterranei, which also helped in delimiting the origin of replication (pA-rep) of the parent plasmid. The strategy involved the cloning of a selectable marker, erythromycin resistance gene (ermE), onto plasmids pULAM2 and pULVK2A (derivatives of pRL1), followed by selection of the hybrid or concatemeric plasmids pRL50 and pRL80 (with large homologous repeats) in Escherichia coli GM2163. These hybrid plasmids were then transferred to A. mediterranei DSM 40773 by electroporation, with selection in the presence of different antibiotics. During the process of transformation and selection in A. mediterranei, pRL50 and pRL80 underwent intraplasmid recombinations, yielding derivatives that retained a common region essential for maintenance and replication, as well as the selected resistance genes. This approach produced several smaller plasmids designated pRL51, pRL52, pRL53, pRL60, pRL81, and pRL82. These plasmids, isolated from A. mediterranei DSM 40773, could be transferred to different Amycolatopsis strains at transformation efficiencies ranging from 0.7 x 10(2) to 4 x 10(4) transformants/microg DNA. The electroporation parameters under which maximum transformation efficiencies were obtained varied from strain to strain. Since the isolation of plasmid DNA from Amycolatopsis strains were extremely difficult, a convenient and rapid method of direct transfer of plasmid DNA, i.e., electroduction, was also developed in which the above-described shuttle plasmids were transferred directly from A. mediterranei to E. coli. In addition, the sequence of the minimal (pA-rep, approximately 1.0 kb) of plasmid pRL51 was determined. The nucleotide base sequence of the pA-rep region did not have any clear similarity to the DNA or amino acid sequences in various databases, suggesting that it is unique.

A gene cloning system for 'Streptomyces toyocaensis'

We explored different methods of introducing DNA into 'Streptomyces toyocaensis' and Streptomyces virginiae to construct stable recombinant strains. Plasmid pIJ702 isolated from Streptomyces lividans transformed protoplasts of 'S. toyocaensis' at a frequency of 7 x 10(3) transformants (mu g DNA)-1. pIJ702 prepared from 'S. toyocaensis' transformed 'S. toyocaensis' protoplasts at a frequency of 1 center dot 5 x 10(5) (mu g DNA)-1, suggesting that 'S. toyocaensis' expresses restriction and modification. Plasmid pRHB126 was transduced by bacteriophage FP43 into 'S. toyocaensis' at a frequency of 1.2 x 10(-6) (p.f.u)-1. Plasmids pOJ436 and pRHB304 were introduced into 'S. toyocaensis' by conjugation from Escherichia coli S17-1 at frequencies of about 2 x 10(-4) and 1 x 10(-4) per recipient, respectively. Analysis of several exconjugants indicated that pOJ436 and pRHB304 inserted into a unique phiC31 attB site and that some of the insertions had minimal deleterious effects on glycopeptide A47934 production. The results indicate that 'S. toyocaensis' is a suitable host for gene cloning, whereas S. virginiae does not appear to be.

Transposition and transduction of plasmid DNA inStreptomyces spp

To expand the application of molecular genetics to many different streptomycete species, we have been developing two potentially widely applicable methodologies: transposon mutagenesis and plasmid transduction. We constructed three transposons from the Streptomyces lividans insertion sequence IS493. Tn5096 and Tn5097 contain an apramycin resistance gene inserted in different orientations between the two open reading frames of IS493. These transposons transpose from different plasmids into many different sites in the Streptomyces griseofuscus chromosome and into its resident linear plasmids. Tn5099 contains a promoterless xylE gene and a hygromycin-resistance gene inserted in IS493 close to one end. Tn5099 transposes in S. griseofuscus giving operon fusions in some cases that drive expression of the xylE gene product, catechol deoxygenase, giving yellow colonies in the presence of catechol. We have also developed plasmid vectors that can be transduced into many streptomycete species by bacteriophage FP43. We describe the characterization of FP43 and mapping of several bacteriophage functions. The region of cloned FP43 DNA essential for plasmid transduction includes the origin for headful packaging.

Properties of the streptomycete temperate bacteriophage FP43

FP43 is a temperate bacteriophage for Streptomyces griseofuscus that forms plaques on many Streptomyces species. FP43 virions contain 56 kb of double-strand DNA that is circularly permuted and terminally redundant, and contains 65% G + C. A physical map of the FP43 genome was constructed, and the origin for headful packaging (pac) was localized to an 8.8-kb region of the genome (hft) that mediates high-frequency transduction by FP43 of plasmid pRHB101. The phage attachment site (attP), a replication origin (rep), a region that inhibits plaque formation (pin), and a 3-kb deletion (rpt) that caused a 100-fold reduction in plasmid transduction were mapped.

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.