O16 Serotype O Antigen Expression in Escherichia coli K-12 May Confer Resistance Against T4 Bacteriophage Infection by Preventing Adsorption

11/17/2017

Amir Wachtel, Alice Guo, Zach Sagorin, Emmanuel Etti

Volume 3
Fall 2016 / Winter 2017

T4 bacteriophage infection of Escherichia coli strain K-12 has been well established as a model for studying virus–host interactions. Lipopolysaccharide (LPS) structure has been shown to be key for such interactions and can impact T4 bacteriophage adsorption and infection. Recently, Chiu et al. demonstrated that E. coli K-12 substrain DFB1655 L9, which expresses O antigen, is resistant to T4 infection whereas the isogenic strain MG1655, which lacks O antigen, is susceptible. The mechanism of DFB1655 L9 resistance to T4 infection is unknown. We hypothesized that O antigen expressed on the surface of E. coli K-12 substrain DFB1655 L9 would decrease T4 bacteriophage adsorption. Since O antigen is located on the outermost portion of LPS we assumed that it sterically blocks the T4 receptors on the core region of LPS. To test this hypothesis, we evaluated differential phage adsorption between strains MG1655 and DFB1655 L9. We used a qPCR assay to measure T4 DNA concentration in E. coli culture supernatants that had been incubated with T4 bacteriophage. Supernatants of E. coli K-12 substrain MG1655 incubated with T4 showed up to 4.9 x 106 fewer copies of the T4 gp23 gene as compared to supernatants of substrain DFB1655 L9. Our data provide preliminary evidence suggesting that O antigen prevents T4 adsorption and confers resistance to infection of E. coli strain DFB1655 L9.