Just like humans, microbes have equipped themselves with tools to recognize and defend themselves against viral invaders. In a continual evolutionary battle between virus and host, CRISPR-Cas acts as a major driving force of strain diversity in host-virus systems.

Patients with cystic fibrosis are often infected by pseudomonas aeruginosa, a bacterium that infects the lungs and prevents breathing, often causing death.

P. aeruginosa itself can also be infected by viruses, which can affect the clinical outcomes of cystic fibrosis patients.