Stable coexistence and transport of lytic phage infections with migrating bacterial hosts

Bacteriophages (phages), viruses that exclusively infect bacteria, coexist with their bacterial hosts across diverse environments at densities exceeding 107 ml-1 in marine surface waters, 108 ml-1 in soils, and 109 ml-1 in the human gut1-6. In contrast, phage lysis of bacteria populations within well-mixed in vitro environments select for the emergence of phage-resistant bacterial mutants7, which in turn select for host-range expansion phage mutants8, leading to the emergence of complex cross-infection networks9, and eventually the collapse of phage populations altogether10,11. This gap in outcome raises a question: what enables long-term phage-bacteria coexistence? Here, we show how interactions in space can facilitate stable coexistence and long-range transport of virulent phage along with migrating bacteria. Through the joint use of theory, simulation, and experiments across multiple phage-bacteria systems, we reveal a chemotaxis-driven mechanism which robustly stabilizes coexistence and dispersal of virulent phages with migrating hosts, while minimizing the potential for coevolutionary-induced collapse of either bacteria or phage. These findings suggest the ecological relevance of spatial interaction mechanisms that reinforce stability between antagonistic partners, in the absence of perpetual cycles of defense and counter-defense, that may be broadly applicable across phage-bacteria systems.