Variably lytic infection dynamics of large Bacteroidetes podovirus phi38:1 against two Cellulophaga baltica host strains

Bacterial viruses (phages) influence global biogeochemical cycles by modulating bacterial mortality, metabolic output and evolution. However, our understanding of phage infections is limited by few methods and environmentally relevant model systems. Prior work showed that Cellulophaga baltica phage phi 38:1 infects its original host lytically, and an alternative host either delayed lytically or lysogenically. Here we investigate these infections through traditional and marker-based approaches, and introduce geneELISA for high-throughput examination of phage-host interactions. All methods confirmed the lytic, original host infection (70-80min latent period;approximately eight phages produced per cell), but alternative host assays were more challenging. A 4.5h experiment detected no phage production by plaque assay, whereas phageFISH and geneELISA revealed phage genome replication and a latent period 150min. Longer experiments (26h) suggested an 11h latent period and a burst size of 871 by plaque assay, whereas phageFISH identified cell lysis starting at <5h and lasting to 11h, but for only 7% to 21.5% of infected cells, respectively, and with approximate to 39 phages produced per cell. These findings help resolve the nature of the alternative host infection as delayed lytic and offer solutions to methodological challenges for studying inefficient phage-host interactions.