Bacteriophage Φ6 (kindly provided by Dr. Paul Turner at Yale University), a model for enveloped RNA viruses including influenza virus [4, 35–37], was propagated using the same method described above, except that the bacterial host was Pseudomonas syringae, which grows at 25°C. Determined by plaque assay, the concentrations of virus stocks were 1010−1011 plaque-forming units (PFU)/mL.