Evolutionary consequences of bacterial resistance to a flagellotropic phage

Bacteria can evolve resistance to bacteriophage attack via mutations that alter phage receptors on the cell surface. Flagellotropic phages bind to motility-enabling flagella, creating an evolutionary trade-off, since losing flagellar function reduces fitness in many environments. We experimentally evolved Escherichia coli populations under selection by flagellotropic phage (chi), on soft-agar swim plates which favor motility. Whole genome sequencing revealed early emergence of non-motile mutants with disrupted motility-genes, followed by motile mutants with flagellin gene mutations. Swim-plate assays and single-cell tracking showed variable motility effects among resistant mutants, with some faster and others slower than ancestors. Increased tumble bias suggested altered flagellar rotation. Kinase-response in the upstream chemotaxis pathway was also remodeled in -resistant mutants. Our findings demonstrate that evolved phage-resistance can cause motility to trade-off or trade-up, revealing diverse evolutionary outcomes under combined selection pressures. TeaserEvolution redesigns bacterial swimming and navigation to escape viruses while maintaining motility in complex environments.