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Plasmid stability in fluctuating environments: population genetics of multi-copy plasmids
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  • J. Carlos R. Hernandez-Beltran,
  • Verónica Miró Pina,
  • Arno Siri-Jegousse,
  • Sandra Palau,
  • Rafael Peña-Miller,
  • Adrian Gonzalez Casanova
J. Carlos R. Hernandez-Beltran

Corresponding Author:[email protected]

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Verónica Miró Pina
Center for Genomic Regulation
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Arno Siri-Jegousse
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Sandra Palau
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Rafael Peña-Miller
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Adrian Gonzalez Casanova
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Plasmids are extra-chromosomal genetic elements that encode a wide variety of phenotypes and can be maintained in bacterial populations through vertical and horizontal transmission, thus increasing bacterial adaptation to hostile environmental conditions like those imposed by antimicrobial substances. To circumvent the segregational instability resulting from randomly distributing plasmids between daughter cells upon division, non-transmissible plasmids tend to be carried in multiple copies per cell, which also results in a metabolic burden to the bacterial host, therefore reducing the overall fitness. This trade-off poses an existential question for plasmids: What is the optimal plasmid copy number? We address this question using a combination of population genetics modeling with microbiology experiments consisting of Escherichia coli K12 bearing a multi-copy plasmid encoding for blaTEM-1, a gene conferring resistance to b-lactam antibiotics. We use a Wright-Fisher model to evaluate the interaction between the above mentioned opposing forces. By numerically determining the optimal plasmid copy number for constant and fluctuating selection regimes, we conclude that plasmid copy number is an optimized evolutionary trait that depends on the rate of environmental fluctuation and balances the benefit between increased stability in the absence of selection with the burden associated with carrying multiple copies of the plasmid.
03 Oct 2022Submitted to Ecology and Evolution
08 Oct 2022Assigned to Editor
08 Oct 2022Submission Checks Completed
08 Oct 2022Review(s) Completed, Editorial Evaluation Pending
14 Oct 2022Editorial Decision: Accept