The Pseudomonas aeruginosa accessory genome elements, including bacterial immune systems effect virulence towards C. elegans

Multicellular animals and bacteria frequently engage in predator-prey and host-pathogen interactions, such as the well-studied relationship between Pseudomonas aeruginosa and the nematode Caenorhabditis elegans. This study investigates the genomic and genetic basis of bacterial-driven variability in P. aeruginosa virulence towards C. elegans. Natural isolates of P. aeruginosa that exhibit diverse genomes display a broad range of virulence towards C. elegans. Using gene association and genetic analysis, we identified accessory genome elements that correlate with virulence, including both known and novel virulence determinants. Among the novel genes, we found a viral-like mobile element, the teg block, that impairs virulence and whose acquisition is restricted by CRISPR-Cas systems. Further genetic and genomic evidence suggests that spacer-targeted elements preferentially associate with lower virulence and suggest a positive, albeit indirect, role for host CRISPR-Cas systems in the restriction of accessory genome elements that may be detrimental to virulence.