Drivers and consequences of bacteriophage host range.

Bacteriophages are obligate parasites of bacteria characterized by the breadth of hosts that they can infect. This "host range" depends on the genotypes and morphologies of the phage and the bacterial host, but also on the environment in which they are interacting. Understanding phage host range is critical to predicting the impacts of these parasites in their natural host communities and their utility as therapeutic agents, but is also key to predicting how phages evolve and in doing so drive evolutionary change in their host populations, including through movement of genes among unrelated bacterial genomes. Here, we explore the drivers of phage infection and host range from the molecular underpinnings of the phage-host interaction to the ecological context in which they occur. We further evaluate the importance of intrinsic, transient, and environmental drivers shaping phage infection and replication, and discuss how each influences host range over evolutionary time. The host range of phages has great consequences in phage-based application strategies, as well as natural community dynamics, and we therefore highlight both recent developments and key open questions in the field as phage-based therapeutics come back into focus.