Polylysogeny magnifies competitiveness of a bacterial pathogen in vivo

The rise of next generation sequencing is revealing a hidden diversity of temperate phages within the microbial community. While a handful of these phages have been well characterized, for the vast majority, the role of phage carriage, and especially multiple phage carriage, is poorly understood. The Liverpool Epidemic Strain of Pseudomonas aeruginosa is an aggressive pathogen in Cystic Fibrosis lung infections that has recently been found to contain several unique prophages within its genome. Here we experimentally investigate the role of two of these phages in vivo, using an insect model of infection. We find that while no benefit is conferred by phage carriage in single bacterial infections, phages confer a large fitness advantage during mixed infections by mediating bacteria-bacteria competition. Differences between the two phages appeared to be associated with the rate at which the competitor acquired the phage, and therefore resistance. However the advantage was greatest in the po...