Flagellotropic bacteriophage selects for evolutionary remodeling of cell motility and chemotaxis in Escherichia coli

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 𝜒 (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 𝜒-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.