Molecular and Genome Evolution of Prokaryotic Plasmids

Plasmids are autonomously replicating extra-chromosomal elements that play a major role in prokaryote ecology and evolution. The study of plasmid evolution has so far focused mostly on their biodiversity and effect on their host ecology and evolution. Nonetheless, the fundamentals of plasmid genome evolution remain to a large extent uncharted territory. Plasmids reside within a host cell that supplies their environmental, energetic and metabolic requirements. Consequently, natural selection operates on plasmids in two hierarchical levels: one component is the plasmid replication and inheritance within the host cell, and the other is the host fitness within the population. Studying the determinants of plasmid evolutionary success thus requires the expansion of classic population genetics theory to populations of plasmids within bacterial cells. The overarching aim of pMolEvol is to create a novel unified framework for plasmid molecular and genome evolution. This includes: 1) to quantify the effect of multilevel drift and selection on plasmid genetic diversity, 2) supply a framework for quantification of plasmid fitness and its effect on plasmid evolution, 3) characterize patterns and rate of plasmid genome evolution. Our conceptual framework will be based on empirical data from plasmid evolution experiments and reconstruction of past events from genomic information. The conceptually novel measures and approaches developed in pMolEvol open up avenues for the extension of classic population genetic theory to prokaryotic organisms. Across all domains of life, genetic information is stored, replicated and translated by similar mechanisms. Focusing on plasmids, we aim to uncover the general principles that govern the evolution of autonomously replicating genetic elements. Our ultimate goal is to describe plasmid evolution from emergence to extinction.