Electron Microscopy to visualize T4 bacteriophage interactions with Escherichia coli strain DFB1655 L9, an isogenic derivative of strain MG1655 engineered to express O16 antigen

Research into the interaction between bacteriophage and bacteria has been a subject of interest since their discovery more than a century ago. This field has seen a resurgence in recent years because of its potential implications in the realm of medicine. Recent studies have shown that a substrain of Escherichia coli with O16 antigen present on their outer membrane are resistant to T4 and T7 bacteriophage-induced lysis, whereas its O16 antigen-absent counterpart is relatively more vulnerable to lysis. However, how this heightened level of resistance is achieved remains unclear. The aim of this study was to observe how the expression of O antigen affects T4 bacteriophage interactions with E. coli strain K-12. To do this we used wild type E. coli MG1655, which does not express O antigen, and isogenic strain DFB1655, into which the wbbL gene was introduced to restore the expression of O antigen. A control strain bearing a deletion of the outer membrane porin, OmpC, was used as a control since T4 is known to use it as a receptor. Transmission electron microscopy (TEM) was used to observe T4 bacteriophage on the surface of E. coli. E. coli substrains possessing O16 antigen had little or no adhered bacteriophage, whereas E. coli without O16 antigen had numerous visible bacteriophages adhered to their surface. In addition, bacterial lysis in the presence of T4 bacteriophage was monitored over time by taking optical density measurements in a lysis assay. When T4 bacteriophage was allowed to infect for an extended period of time, substrains possessing O16 antigen exhibited lower rates of lysis compared to those lacking O16 antigen. Our observations indicate that the presence of O16 antigen on the surface of E. coli confers protections against T4 bacteriophage-induced lysis, likely through reduced interactions with the cell surface. However, O16 antigen does not appear to provide complete immunity to phage adsorption, but rather protection that delays infection.