Temporal dynamics of RNA phage infection reveal bacterial recovery despite ongoing viral replication
Bacterial defenses against DNA phages are well documented, yet responses to RNA phages remain largely unexplored. Here, we characterize the population dynamics and host responses of Escherichia coli infected by the lytic RNA phage MS2 across multiple timescales, using bulk and single-cell transcriptomics, fluorescence microscopy, whole-genome sequencing, and genetic perturbations. Despite rapid viral takeover and extensive cell death, the bacterial population subsequently rebounds, revealing an unusual state in which host proliferation persists under intense phage pressure. Early in infection, heterogeneous subpopulations are evident, including one with low or undetectable viral transcript levels, low expression of the F-plasmid genes encoding the F-pilus (the MS2 receptor), and a distinct metabolic state. Strikingly, the rebounding population carries MS2 RNA in the great majority of cells, with evidence for active viral replication and continued cell division despite high viral loads. This rebound coincides with strong induction of biofilm-associated genes, including the pga operon, which synthesizes the biofilm-matrix exopolysaccharide PNAG. Deletion of pgaA causes earlier population decline and reduced population survival, indicating that pga-dependent matrix production delays viral lysis. Over longer timescales, phage-exposed populations show heterogeneous F-plasmid prevalence and plasmid-wide expression, consistent with dynamic cycling between plasmid-bearing and plasmid-free states: MS2 selects against F-plasmid-bearing cells, whereas conjugation may restore plasmid carriage. We propose that the biofilm-associated matrix delays viral lysis relative to continued cell division, long enough for rare F-plasmid-free daughter cells to arise and expand. Our results suggest that bacterial survival is determined by a dynamic race between viral lysis and host-cell division.