Contrasted coevolutionary dynamics between a bacterial pathogen and its bacteriophages

Scientists have long debated the dynamic form of perpetual reciprocal adaptations, or coevolution, between hosts and their parasites. The two main types of antagonistic coevolution described to date are arms race dynamics, in which interaction traits escalate through time, and fluctuating selection dynamics, in which traits cycle through time. We used experimental evolution between Pseudomonas aeruginosa and a panel of its lytic phages and found the full known range of coevolutionary dynamics. We argue that the coevolutionary pattern is determined by whether phages typically adsorb directly to receptors on the bacterial outer membrane or instead use retractable type IV pili as a primary or alternative site. Our results have applications in the use of phages as therapeutics or disinfectants to control bacterial pathogens.