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Isolation and characterization of membrane-associated form of penicillase plasmid (pI524) DNA in Staphylococcus
1Department of Biology, Florida A&M University, Tallahassee 32307.
Abstract:
Our studies on the association of penicillinase plasmid (pI524) DNA with its host bacterial (Staphylococcus aureus) membrane revealed that the membrane-associated forms of this plasmid could be isolated from exponentially grown cells lysed on neutral sucrose gradient. Analysis of putative plasmid-membrane complexes isolated from the clear lysates on sucrose gradients indicated that approximately 23% of plasmid (pI524) DNA was stably associated with the bacterial cell membrane fractions. This suggested that one of the three or four copies of this plasmid per cell was complexed to the cellular membrane. Examination of the effect of various enzymes, e.g., ribonuclease and protease, as well as antibiotics (rifampicin and chloramphenicol), on complexing have shown the possible involvement of protein(s) rather than RNA in mediating the complexing of this plasmid to the cell membrane. The specificity of plasmid pI524 to its host cell membrane was observed in an experiment where R6k was included in binding assay.
Insights
Penicillinase plasmid (pI524) DNA stably associates with Staphylococcus aureus cell membranes, involving proteins. This specific plasmid-membrane interaction suggests a key role in bacterial processes.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Plasmids are extrachromosomal DNA elements crucial for bacterial adaptation and virulence.
- Understanding plasmid-host interactions, particularly membrane association, is vital for deciphering their biological roles.
- Staphylococcus aureus is a significant human pathogen where plasmid-mediated traits are common.
Purpose of the Study:
- To investigate the association of the penicillinase plasmid (pI524) with the cell membrane of Staphylococcus aureus.
- To determine the nature of the interaction and identify components involved in plasmid-membrane complex formation.
Main Methods:
- Isolation of membrane-associated plasmid DNA from exponentially growing Staphylococcus aureus cells using neutral sucrose gradient centrifugation.
- Analysis of plasmid-membrane complexes through enzymatic treatments (ribonuclease, protease) and antibiotic exposure (rifampicin, chloramphenicol).
- Assessment of binding specificity using a heterologous plasmid (R6k) in binding assays.
Main Results:
- Approximately 23% of plasmid pI524 DNA was found stably associated with Staphylococcus aureus cell membrane fractions.
- The association was mediated by protein components rather than RNA.
- Plasmid pI524 exhibited specificity for its host cell membrane, as demonstrated by binding assays.
Conclusions:
- Plasmid pI524 forms stable complexes with the Staphylococcus aureus cell membrane, with approximately one copy per cell involved.
- Protein-mediated interactions are responsible for anchoring the plasmid to the bacterial membrane.
- The observed specificity suggests a targeted mechanism for plasmid-membrane association in Staphylococcus aureus.