Evolution and ecology of adaptive immunity in bacteria

The viruses that infect bacteria, known as phages, are the most abundant biological entities on earth. They shape bacterial evolution and contribute to global biogeochemical cycling through bacterial mortality. Subsequently bacteria have evolved diverse mechanisms with which to evade these viral predators.

Although many of these defence systems have been well characterised much less is understood about the ecological conditions that determine when one form of defence is favoured over another. I will present the results from several studies that focus on the role of ecological conditions in shaping one such defence: CRISPR-Cas.

The work presented will include experimental evolution of the human pathogen Pseudomonas aeruginosa, as well as analysis of metagenomic data from natural microbial communities. Together the results demonstrate that the viral community is a strong selective force in maintaining bacterial immunity and how resilient this immunity is over time.

Understanding the prevalence of these bacterial immune systems may have important consequences for the use of phages as a therapeutic agent in treating bacterial infections, particularly in light of increasing antimicrobial resistance.