Methods to Study Fitness and Compensatory Adaptation in Plasmid-Carrying Bacteria
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Mobile genetic elements such as plasmids mediate horizontal gene transfer in prokaryotes, promoting bacterial adaptation and evolution. Despite the potential advantages conferred by these genetic elements, plasmids can also produce a fitness cost when they arrive to a new host. This initial burden is one of the main limits to the spread of plasmids in bacterial populations. However, plasmid costs can be ameliorated over time through compensatory mutations in the plasmid or the chromosome (compensatory adaptation). Understanding the origin of the cost produced by plasmids and the potential for compensatory adaptation is crucial to predict the spread and evolution of plasmid-mediated traits, such as antibiotic resistance. Here, we describe a simple protocol designed to analyze the fitness effects of a plasmid in a new host bacterium. We also provide a method to examine the potential for compensatory adaptation, using experimental evolution, and to elucidate if compensation originates in the plasmid, the bacterium, or both.
Key wordsEvolution Fitness Plasmid Experimental evolution Compensatory adaptation Antibiotic resistance Coevolution
This work was supported by the Instituto de Salud Carlos III (Plan Estatal de I + D + i 2013–2016)—grants CP15-00012, PI16-00860, and CIBER (CB06/02/0053) actions—and cofinanced by the European Development Regional Fund “A way to achieve Europe” (ERDF) and by the European Research Council under the European Union’s Horizon 2020 research and innovation program (ERC grant agreement no. 757440-PLASREVOLUTION). J.R.B. is a recipient of a Juan de la Cierva Fellowship, Ministerio de Economı́a Industria y Competitividad (FJCI-2016-30019).
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