The Darwinian fitness of extrachromosomal genetic elements

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 is expected to operate 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. In recent years my research group has been studying the implications of different levels of selection, and drift, to plasmid genome evolution. In the seminar I will present our current results, e.g., on the evolution of plasmid inheritance under non-selective conditions, how selection for plasmid functions affects plasmid evolution, and why are there no essential genes on plasmids.