Coevolutionary training of phages can be more successful in several small, relative to single large, habitats.

Evolutionary training of phages can help to counter bacterial resistance evolution. Here, we address whether metapopulation processes can enhance the evolution of phage infectivity. Our experiment with a model bacterium-phage system supported a prediction of long-term fluctuating selection dynamics. Specifically, metapopulations of several small habitats showed greater total infectivity ranges by supporting more diverse phages, compared with single large populations. Crucially, the advantage of several small habitats was conditioned on blocking bacterial dispersal within metapopulations. We conclude that well-designed metapopulation training programs can be useful for quick and easy preparation of cocktail phage materials.