Death and chemotaxis: Bacterial chemotaxis enables collective escape from phage predation

Bacteriophages ("phage") are viruses that prey on bacteria in diverse environments, from biological tissues to soils. In many of these environments, bacterial hosts are constantly migrating, yet how bacterial migration is influenced by phage predation remains poorly understood. Using transparent granular hydrogels that mimic natural habitats, we directly visualize populations of motile Escherichia coli encountering lytic T4 phage. Unexpectedly, we find that even in phage-rich environments, bacteria successfully form chemotactic fronts that enable them to migrate over large distances without necessarily requiring new phage resistance mutations. At low phage concentrations, the front is indistinguishable from a phage-free control, and the population remains largely susceptible; at higher concentrations, the susceptible population initially collapses, and the front is reestablished by a less susceptible subpopulation enriched under intense predation. Higher phage concentrations delay front formation but not steady-state front speed or shape. By combining our experiments with biophysical modeling, we demonstrate that this phenomenon reflects a competition between collective chemotactic migration and phage predation, quantified by a dimensionless "escape parameter," in which sufficiently rapid migration allows the population to outpace the spreading infection. This work thus provides mechanistic insight into how cell motility shapes phage-bacteria interactions in spatially extended environments.