<b>Characterization of S</b><b><i>iphoviridae </i></b><b>Bacteriophage Induction of Lytic Cycle of Prophage in </b><b><i>Serratia marcescens</i></b>

<p dir="ltr">Isolation and characterization of a <i>Salmonella Siphoviriade</i>-like bacteriophage (PNW_<i>Siphoviridae</i>) was shown to lyse wild-type <i>Serratia marcescens</i> in a temperature and strain-dependent manner. Glycosylated residues of lipopolysaccharide (LPS) on WT <i>S. marcescens </i>were hypothesized to be the primary receptor for the phage through isolation of phage resistant mutants, suggesting a mechanism for strain and temperature specificity through LPS variability. To test this, we aimed to adapt PNW_<i>Siphoviridae </i>to infect <i>S. marcescens </i>strain Db11, a non-permissive strain, through a series of broth culture propagations. Lytic plaques were observed and the isolated phage was shown to be a generalist phage, infecting several strains of <i>S. marcescens </i>via plaque assay in the sixth passage (P6). Genomic sequencing and bioinformatic analysis surprisingly revealed that P6 is not an evolved form of PNW_<i>Siphoviridae</i> but rather <i>Salmon_118970_sal3</i> (PNW<i>_sal3</i>), a prophage from <i>S. marcescens</i>. In this study, we aimed to characterize PNW_<i>sal3</i> and determine pathways that triggered the expression of the prophage following infection of PNW_<i>Siphoviridae</i>. Bioinformatic and genomic analysis of <i>Salmon_118970_sal3 </i>revealed that this temperate phage can be found in several strains of <i>S. marcescens</i>, with differences in genome composition and infection kinetics that demonstrate the diversity of phages and complexities of host-phage interactions. Due to the sensitivity of WT to PNW_<i>Siphoviridae</i>, we hypothesized that PNW_<i>Siphoviridae </i>infection induced the SOS response in WT <i>S. marcescens</i>, leading the lysogenic prophage to become lytic. Although transcriptomic analysis during infection did not detect upregulation of key SOS genes, we report a general host response of WT <i>S. marcescens</i> to phage infection. Few reports have identified virulent phage as a regulator of prophage induction, and therefore this work could help aid our understanding of phage population dynamics and phage diversity in a ubiquitous bacterium such as <i>S. marcescens</i>.</p>