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Mutations in prophage phi11 that impair the transducibility of their Staphylococcus aureus lysogens for methicillin
Abstract:
Methicillin resistance (mec) is not transduced into Staphylococcus aureus 8325-4, but is transduced into this host after it has been lysogenized with phage phi11 and has acquired the penicillinase plasmid pI524 by a separate transduction (Cohen and Sweeney, 1970, 1973). Strain 8325-4 is competent for transformation of typical plasmid or chromosomal markers and for mec only if it is lysogenic for phi11 or a related prophage (Sjöström et al., 1974, 1975). A mutant strain of phi11 that was temperature sensitive (Ts) for vegetative multiplication did not mediate competence for transformation of its 8325-4 lysogen if the lysogen had been grown at a nonpermissive temperature (Sjöström and Philipson, 1974). We isolated four Ts mutants of phi11 that did not mediate transducibility of their 8325-4(pI524) lysogens for mec after growth at nonpermissive temperatures (40 to 42 degrees C). Transduction of typical plasmid or chromosomal markers was not affected. These phi11-Ts mutants mediated normal competence of their lysogens for transformation of a tetracycline resistance plasmid. Similarly, phi11-Ts mutants that rendered their lysogens temperature sensitive for transformation did not depress the frequency of transduction of mec. These two types of phi11-Ts mutants fell into two different genetic complementation groups that differed in the physiology of deoxyribonucleic acid synthesis and in the time of expression of the mutations during a single-burst growth cycle at a nonpermissive temperature. A virulent mutant of phi11, which plaqued with 100% efficiency on 8325(phi11), also failed to condition strain 8325-4 for transducibility of mec but retained the ability to confer competence for transformation of a tetracycline resistance plasmid. Different genetic loci and physiological functions are involved in phi11 mutations that affect transducibility of mec and those that affect competence for transformation of markers generally in S. aureus 8325-4.
Insights
Bacteriophage phi11 mutants were studied for their ability to transfer methicillin resistance (mec) in Staphylococcus aureus. Specific phi11 mutants impaired mec transduction but not general marker transformation, indicating distinct genetic mechanisms.
Area of Science:
- Microbiology
- Bacteriology
- Molecular Biology
Background:
- Methicillin resistance (mec) transduction in Staphylococcus aureus 8325-4 is dependent on lysogeny with phage phi11.
- Previous studies showed that temperature-sensitive (Ts) phi11 mutants can impair transformation competence in lysogenic strains.
Purpose of the Study:
- To investigate the role of specific bacteriophage phi11 genes in the transduction of methicillin resistance (mec) in Staphylococcus aureus.
- To differentiate the genetic and physiological functions involved in mec transduction versus general marker transformation.
Main Methods:
- Isolation and characterization of four temperature-sensitive (Ts) mutants of phage phi11.
- Assessing the ability of these phi11 mutants to mediate transduction of methicillin resistance (mec) and tetracycline resistance plasmids in Staphylococcus aureus 8325-4.
- Genetic complementation analysis and examination of deoxyribonucleic acid synthesis during phage growth.
Main Results:
- Four phi11-Ts mutants failed to mediate mec transduction in Staphylococcus aureus 8325-4(pI524) at nonpermissive temperatures, while general plasmid and chromosomal marker transduction remained unaffected.
- These mutants supported normal competence for tetracycline resistance plasmid transformation, indicating a specific defect in mec transduction.
- Complementation groups revealed distinct physiological roles and expression times for mutations affecting mec transduction versus general transformation competence.
Conclusions:
- Distinct genetic loci and physiological functions govern bacteriophage phi11-mediated transduction of methicillin resistance compared to general transformation competence in Staphylococcus aureus.
- The findings provide insights into the specific mechanisms underlying the transfer of antibiotic resistance genes via bacteriophage transduction.