<b>Viral Permissiveness Characterization of a Novel Siphovirus (Serratia phage PNW1) in </b><b><i>Serratia marcescens </i></b><b>and the Role of LPS as the Phage Receptor</b>

<p dir="ltr">Characterization of an isolated siphovirus phage (<i>Serratia</i><i> </i>phage<i> </i>PNW1) identified variable lytic susceptibility by strains of the ubiquitous and nosocomial pathogen <i>Serratia marcescens</i> in a temperature dependent manner. Whole genome sequence analysis of <i>S. marcescens</i> escape mutants established glycosylated residues of lipopolysaccharides (LPS) as the site of phage adsorption. Heterogeneity of the outer membrane glycoconjugate LPS is known to influence bacteriophage adsorption and is dependent on environmental conditions such as temperature. The structure of LPS in <i>Serratia</i> strains has yet to be thoroughly examined. To further understand strain specificity and elucidate variability of LPS among <i>S. marcescens</i><i> </i>strains, we took a bioinformatic and experimental approach. Comparative analysis of the LPS biosynthetic gene cluster identified key differences that could equate to key phenotypic differences among strains. LPS isolated from four strains incubated at two temperatures using the Trizol-like solution method (T-sol), and gel electrophoresis identified marked variability in permissive and non-permissive strains. We hypothesized <i>Serratia</i><i> </i>phage PNW1 used host LPS as a binding site for adsorption. Preliminary results demonstrated that extracted LPS protected <i>S. marcescens</i> from phage lysis, which indicated LPS as the phage receptor. Analysis of LPS structure in susceptible and non-susceptible strains by MALDI-TOF will yield a greater understanding of the interaction between <i>S. marcescens</i><i> </i>and <i>Serratia</i><i> </i>phage PNW1, as well as the heterogeneity of LPS. Together, this work identified LPS as the main receptor for <i>Serratia</i><i> </i>phage PNW1 attachment to WT <i>S. marcescens</i> during a lytic infection, which may explain observed differences in phenotypic outcomes related to temperature and strain specificity of this phage.</p>