Novel <i>Escherichia coli Dhillonvirus</i> DH23 is Able to Grow on the Host Cells at Late Growth Phases

Background: The majority of bacteriophages stop replicating once the host culture approaches the stationary phase. Only a few bacteriophages are able to replicate in host cells at the transition to, or already in, the early stationary phase of growth (early stationary phase infective, eSPI phages) have been characterized so far. Materials and Methods: The coliphage DH23 was isolated from the river water using an enrichment procedure with a stationary phase culture of the host. Genomic sequencing, epigenetic modifications detection, and morphological and biological characterization were performed. Results: DH23 is a small siphovirus with a genome of 44,682 b.p. Phylogenetic analysis suggests that DH23 may be considered as a new species within the Dhillonvirus genus, closely related to Sodalis phage SO-1 and coliphage TheodorHerzl. Phage DH23 plaques continue to expand for several days of incubation and it is able to form plaques when applied to already mature 24 h-old host lawn. Conclusions: Bacteriophage DH23 features an eSPI phenotype very similar to phage T7. Expanding the number of characterized eSPI coliphages may facilitate deciphering the molecular basis of eSPI phenotype and development of new eSPI platforms for phage therapy or other applications.