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.

Who is this course for?

This webinar is suitable for students, biologists, bioinformaticians and researchers interested in learning about pangenomics. No prior knowledge of the field is required, but an undergraduate level of biology would be helpful.

This event is part of a broader webinar series exploring concepts, methods and resources in pangenomics. For more information about the series and its webinars, please visit the following link: "Concepts, methods and resources in pangenomics".

Outcomes

By the end of this webinar, you will be able to:

• Explain how the accessory genome differs from the core genome and why it is central to bacterial adaptability.
• Describe the role of negative frequency-dependent selection in maintaining accessory gene diversity and multi-strain population structures.
• Discuss examples from pathogens where accessory genes shape vaccine response, antimicrobial resistance, and colonisation success.
• Evaluate how evolutionary models using accessory gene frequencies can forecast pathogen population changes under intervention.

DOI: 10.6019/TOL.Evo-accessory-genome-w.2025.00001.1

This webinar took place on 08 October 2025. Please click the 'Watch video' button to view the recording.