Abstract

Beyond the scope of what our unaided eyes can see is a diverse and rich microbial community that greatly impacts each of our lives. Bacteria are microscopic organisms that can grow, develop, divide, and even rapidly evolve to adapt to new changes in their environment. Because of this, bacteria have gained the ability to thrive in extreme biological niches ranging from the high temperature and pressure surrounding hydrothermal vents to the harsh acidic conditions of our stomachs. One adaptation attracting attention, however, is their capability to survive in the presence of common and even last-resort antibiotics. The WHO recently reported that antibiotic resistant infections cost the lives of 5 million people globally in 2019 and are only projected to increase (4). This global public health concern mandates the development of alternative treatments to combat the increase of antibiotic resistant infections. One possibility being explored is the use of bacteriophages, which naturally target and kill very specific bacteria. While successful phage therapeutics have been performed, many others have not proceeded beyond their clinical trials (8-10). Phage infection is a multi-step process that involves: 1) host attachment, 2) host takeover, 3) phage replication, and 4) phage release. Each step contains an intricate network of interactions which can be derailed upon the acquisition of mutations. Because of this, both phage and bacteria are constantly evolving to overcome the response of the other. Further understanding the details of these interactions and how phages evolve to infect resistant or new hosts could enable the design of alternative antibiotic therapies. In response, I focused on the first step of phage infection and applied molecular biology techniques to identify and characterize the binding profiles of three novel coliphages onto the FhuA outer membrane porin. The influence of the presence of lipopolysaccharide on receptor recognition was also explored to give a more detailed profile of phage binding. The predicted phylogenetic histories of their phage tail fibers were also compared to highlight instances where positive selective pressure or recombination may have altered their receptor binding sites. Genomic and proteomic comparisons and LC-MS/MS were performed on five clinically relevant Klebsiella phages and host range analysis confirmed their ability to infect antibiotic resistant Klebsiella strains. In summary, I have applied in vitro and in silico analysis to outline the structures involved in FhuA-dependent phage attachment and explored the potential evolutionary history of FhuA-dependent tail fibers. Additionally, this work identifies a cocktail of Klebsiella phages that may have therapeutic value and highlights how differences in their distal tail fibers may define their unique host ranges. This work emphasizes the important role tail fibers play in the initial step of phage infection along with how the evolution of these proteins can lead to altered host ranges. Further understanding these interactions and how phages adapt to combat phage resistance could give key insight into the evaluation of phages as potential therapeutics.

Degree

PhD

College and Department

Life Sciences; Microbiology and Molecular Biology

Rights

https://lib.byu.edu/about/copyright/