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Published on: September 11, 2020
Fitness of the pMV158 replicon in Streptococcus pneumoniae
Ana María Hernández-Arriaga1, Manuel Espinosa, Gloria del Solar
1Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
Abstract:
Promiscuous, rolling-circle replication plasmid pMV158 determines tetracycline resistance to its host and can be mobilized by conjugation. Plasmid pLS1 is a deletion derivative of pMV158 that has lost its conjugative mobilization ability. Both plasmids replicate efficiently and are stably inherited in Streptococcus pneumoniae. We have analyzed the effect of pMV158 and pLS1 carriage on the bacterial growth rate. Whereas the parental plasmid does not significantly modify the cell doubling time, pLS1 slows down the growth of the bacterial host by 8-9%. The bases of the differential burden caused by pMV158 and pLS1 carriage are not yet understood. The negligible cost of the pMV158 parental natural plasmid on the host might explain the prevalence of small, multicopy, rolling-circle replication plasmids, even though they lack any selectable trait.
Insights
The promiscuous plasmid pMV158 has no effect on bacterial growth, but its derivative pLS1 slows Streptococcus pneumoniae growth by 8-9%. This difference in host burden may explain the prevalence of naturally occurring plasmids.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Promiscuous rolling-circle replication plasmid pMV158 confers tetracycline resistance and is conjugally mobilizable.
- Plasmid pLS1, a derivative of pMV158, lacks conjugative mobilization ability but retains efficient replication and stable inheritance in Streptococcus pneumoniae.
Purpose of the Study:
- To investigate the impact of pMV158 and pLS1 plasmid carriage on the growth rate of Streptococcus pneumoniae.
- To understand the differential burden imposed by these two related plasmids on their bacterial host.
Main Methods:
- Comparative analysis of bacterial growth rates.
- Culturing of Streptococcus pneumoniae strains harboring either pMV158 or pLS1.
Main Results:
- Carriage of the parental plasmid pMV158 did not significantly alter the bacterial cell doubling time.
- Plasmid pLS1 carriage resulted in a noticeable growth rate reduction of 8-9% in Streptococcus pneumoniae.
- The underlying reasons for the differential growth burden between pMV158 and pLS1 remain undetermined.
Conclusions:
- The negligible cost associated with pMV158 suggests a potential explanation for the widespread occurrence of small, multicopy, rolling-circle replication plasmids, even in the absence of selectable traits.
- The observed growth defect caused by pLS1 highlights the potential fitness costs associated with plasmid maintenance and replication in bacteria.
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