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Abstract:
Plasmid deoxyribonucleic acid has been detected in three related laboratory strains of Streptococcus pneumoniae. Strains D39S, R36, and R36NC each contain a minimum of two copies per cell of a 2.0-megadalton plasmid (pDP1). A plasmid twice as large as this smaller one is also present in much lower quantity in these strains, but neither plasmid is present in four strains related to these or in a drug-resistant clinical isolate from Paris. The plasmid yield was not amplified in the presence of chloramphenicol. No phenotype has been correlated with the presence of pDP1, which has existed in strains carried for many years in laboratory collections.
Insights
Researchers detected plasmid deoxyribonucleic acid (DNA) in specific Streptococcus pneumoniae lab strains. These strains contain a 2.0-megadalton plasmid (pDP1), but its function remains unknown.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pneumoniae is a significant human pathogen.
- Plasmids are extrachromosomal DNA elements that can confer advantageous traits.
- The presence and role of plasmids in S. pneumoniae laboratory strains are not fully characterized.
Purpose of the Study:
- To investigate the presence and characteristics of plasmid DNA in specific laboratory strains of Streptococcus pneumoniae.
- To determine if plasmid presence correlates with any observable phenotype or antibiotic resistance.
Main Methods:
- Plasmid DNA extraction from Streptococcus pneumoniae strains.
- Agarose gel electrophoresis to analyze plasmid size and quantity.
- Comparison of plasmid profiles across related laboratory and clinical isolates.
Main Results:
- Three related laboratory strains (D39S, R36, R36NC) were found to contain at least two copies of a 2.0-megadalton plasmid (pDP1) per cell.
- A larger plasmid, approximately twice the size of pDP1, was also detected in low quantities in these strains.
- Neither plasmid was detected in four related strains or a drug-resistant clinical isolate.
- Plasmid yield was not increased by chloramphenicol treatment.
- No specific phenotype was associated with the presence of pDP1.
Conclusions:
- Specific laboratory strains of Streptococcus pneumoniae harbor distinct plasmids, including a prevalent 2.0-megadalton plasmid (pDP1).
- The presence of these plasmids does not appear to confer a selectable advantage or be linked to antibiotic resistance in the studied strains.
- Further research is needed to elucidate the function and evolutionary significance of pDP1 in S. pneumoniae.