Rescue of O16 Antigen expression in E. coli strain MG1655 Prevents Adsorption of T4 Bacteriophage

O antigen is the outermost component of lipopolysaccharide and is expressed on the surface of Gram-negative bacteria. The O antigen O16 in Escherichia coli K-12 has been associated with resistance to T4 bacteriophage infection and its biosynthesis requires functional components encoded by the rfb locus, including wbbL which encodes a rhamnose transferase. Previous experiments have demonstrated that the presence of functional wbbL conveys E. coli strains complete resistance to T4 bacteriophage mediated lysis, while disrupted wbbL leaves them susceptible. However, the mechanism through which this resistance occurs is still unclear. Due to O16 antigen being a surface molecule, we hypothesized that the presence of wbbL prevents T4 bacteriophage adsorption onto the surface of E. coli K-12. In this study, we investigated T4 bacteriophage adsorption ability via a chloroform-based adsorption assay on both E. coli MG1655 and DFB1655 L9. These are two completely isogenic strains differing only in wbbL functionality, with MG1655 unable to produce O16. We found that the number of unadsorbed T4 bacteriophage decreased to 17% of the original concentration over 15 minutes when incubated with MG1655, presenting an adsorption rate constant of 2.8 x 10-9 mL/min(cfu). When incubated with DFB1655 L9 however, the number of unadsorbed T4 bacteriophage did not decrease even after 25 minutes of incubation, indicating that T4 bacteriophage can adsorb to MG1655 but not to DFB1655 L9. Since these two strains are isogenic except for wbbL, we conclude that the presence of functional wbbL in E. coli strain DFB1655 L9 prevents T4 bacteriophage adsorption.