Liu, Aileen-The role of Pseudomonas aeruginosa accessory genes tfpY and tfpZ in bacteriophage defenses (Dr. Lori Burrows)

The role of Pseudomonas aeruginosa accessory genes tfpY and tfpZ in bacteriophage defenses

Pseudomonas aeruginosa (Pa) is an opportunistic pathogen that is a major causative agent of hospital-acquired infections. Pa have long filaments on the cell surface known as type IV pili (T4P),  which are virulence factors. Tail proteins on bacteriophages have evolved to recognize T4P as receptors,  therefore,  taking advantage of T4P as a phage receptor could be used as a therapeutic against antibiotic resistant strains of Pa. Bacteria have also evolved a number of phage defense mechanisms which can make Pa resistant to phage therapy. We analyzed a library of pilus-specific phages to characterize a novel phage defense system in Group III and Group V Pa pilins to determine if accessory genes tfpX and tfpY are involved in anti-phage defenses. We identified six phages that showed a decrease in bacterial cell death when TfpY and TfpZ were present compared to when the proteins were absent. Pa subcultures with and without tfpX and tfpY were challenged with our phages and optical density (OD) tests revealed that bacterial growth was higher in strains with the accessory genes compared to when the genes were absent. Twitching assays revealed that the number of surface pili decreased when the accessory genes were removed,  suggesting TfpY and TfpZ may be involved in changing the structure of the pili to prevent phage adsorption. Our tests reveal that accessory genes tfpX and tfpY play a role in evading phage infection,  which should be considered when making or adjuvants against multi-drug resistant Pa.