The accessory genome, the set of genes variably present across members of a bacterial species, plays a central role in shaping microbial diversity and adaptation. Instead of a random collection of mobile elements, evidence has shown that the accessory genome is structured by selective forces, particularly negative frequency-dependent selection, and underpins the long-term stability of multi-strain bacterial populations. Accessory loci are implicated in host interactions, inter-bacterial competition, and responses to clinical interventions such as vaccination and antibiotic consumption, making them a cradle of adaptive potential. 

In this webinar, we will explore how accessory genomes evolve, why their composition remains stable despite turnover of lineages, and how this evolutionary perspective allows us to better understand pathogen persistence and predict responses to selective pressures.