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Vibrio cholerae conjugative plasmid pSJ15 contains transposable prophage dVcA1
Abstract:
Evidence is presented that defective prophage dVcA1 in Vibrio cholerae strain 162 was transposed to the hybrid P::Tn1 plasmid pSJ5. Properties of the resulting conjugative plasmid, pSJ15, indicated that bacteriophage VcA1, like coliphage Mu, can insert at many sites. By analogy with other Hfr-like donors, the high-frequency, polarized chromosomal transfer mediated by plasmid pSJ15 in strain 162 appeared to depend on plasmid integration through the homologous dVcA1 sequences in both replicons. When strain 162(pSJ15) donors were mated to the nonlysogenic El Tor strain RJ1, many potential ampicillin-resistant transconjugants were zygotically induced. However, surviving transconjugants (i) were immune to phage VcA1, (ii) cotransferred immunity and ampicillin resistance to nonlysogenic recipients, and (iii) did not preferentially transfer any chromosomal markers. Recombinant plasmids that transferred wild-type VcA1 prophages were readily isolated from strain RJ1 (VcA1+) lysogens that contained plasmid pSJ15. Physical measurements revealed that plasmid pSJ15 and the recombinant plasmids were about one VcA1 genome (22 to 24 megadaltons) larger than the 51-megadalton pSJ5 plasmid. Similar Hfr-like donors were constructed by introducing plasmid pSJ15 into different strain RJ1 (VcA1+) lysogens. Transfer properties of these donors indicated that the VcA1 prophage was integrated at several sites in the strain RJ1 chromosome.
Insights
Defective Vibrio cholerae prophage dVcA1 integrated into a plasmid, creating a conjugative plasmid that mediates high-frequency chromosomal transfer. This phage can insert at multiple sites, influencing bacterial genetics and phage behavior.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacteriophages can integrate into bacterial genomes, influencing host properties.
- Transposons and plasmids play key roles in bacterial genetic exchange and evolution.
- Understanding phage integration and transfer mechanisms is crucial for bacterial genetics.
Purpose of the Study:
- To investigate the transposition of defective prophage dVcA1 in Vibrio cholerae.
- To characterize the properties of a novel conjugative plasmid (pSJ15) formed by this integration.
- To elucidate the mechanism of high-frequency chromosomal transfer mediated by the VcA1 prophage.
Main Methods:
- Plasmid conjugation experiments with Vibrio cholerae strains.
- Isolation and characterization of recombinant plasmids.
- Physical mapping and size determination of plasmids.
- Analysis of chromosomal marker transfer during mating.
Main Results:
- Defective prophage dVcA1 transposed to plasmid pSJ5, forming conjugative plasmid pSJ15.
- Plasmid pSJ15 mediated high-frequency, polarized chromosomal transfer in Vibrio cholerae strain 162.
- Transconjugants exhibited phage immunity and cotransferred resistance, indicating stable integration.
- VcA1 prophage integration sites were found to be numerous in both donor and recipient strains.
Conclusions:
- Bacteriophage VcA1, similar to coliphage Mu, exhibits broad site-specific integration capabilities.
- Plasmid pSJ15 functions as an Hfr-like donor, facilitating efficient genetic exchange.
- The VcA1 prophage's ability to integrate at multiple chromosomal locations has significant implications for Vibrio cholerae genetics.