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 a potential evolutionary trade-off, since losing flagellar function can reduce fitness in many environments. Phage-resistance studies typically characterize this trade-off using population-mean phenotypes, but selection can act on, and reshape, the underlying single-cell distribution of a trait in ways that mean values alone do not capture. Here, we exploit the well-developed and experimentally tractable model system of Escherichia coli-phage {chi} (chi) to ask how evolved resistance to a flagellotropic phage reshapes single-cell motility phenotypes, not just their population averages. We experimentally evolved E. coli populations under selection by {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, {chi}-resistant mutants carrying flagellin mutations. Swim-plate assays and single-cell tracking revealed heterogeneous motility outcomes among resistant lineages: some recovered or exceeded ancestor-level motility while others swam slower than ancestors, demonstrating that trade-offs and trade-ups can both arise from selection by the same phage- an outcome rarely captured in a single phage-resistance study. Single-cell tracking further showed that resistant lineages evolved increased tumble bias and altered swimming speed distributions, revealing shifts in trait heterogeneity invisible to mean-based measures. At the ensemble level, resistant mutants also showed remodeled kinase-response output in the upstream chemotaxis signaling pathway, indicating that resistance reshapes motility behavior both through receptor-level and signaling-level adaptation. Together, these findings demonstrate that evolved phage-resistance reshapes the receptor-linked (motility) phenotype across multiple phenotypic scales: from single-cell behavioral distributions to signaling network output, producing diverse and previously undocumented evolutionary outcomes under combined selection pressures.