EVOLUTION OF BACTERIOPHAGE HOST ATTACHMENT USING DET7 AS A MODEL

Bacteriophage fulfill a crucial role in maintaining bacterial population levels as well as being a driving force behind bacterial diversity. Bacteria display a huge variety of cell-surface molecules, and these cell surface antigens play a central role in bacterial virulence as well as being recognition sites of phage infection. Due to the wide range in variation of antigens, bacteriophages (phages) have adapted a variety of cell surface recognition systems. All phage with contractile tails likely share a common ancestor and therefore share structural similarity. The best characterized contractile tail is that of phage T4 that shares remarkable similarity to the core tail genes of Det7. All of the major structural tail proteins and their T4 homologs have been biochemically identified in Det7. Despite the similarity in tail structure, there is no similarity in the host attachment proteins between Det7 and T4. Most phage are equipped with only one type of primary cell adhesion protein, with the best characterized phage adhesion systems being those of P22 and T4. Phage Det7, a member of the recently identified Viunalikevirus family, carries five different cell attachment proteins. Det7 gp5 shares amino acid and structural similarity in host attachment proteins with P22 and 9NA. The amino acid sequences of the active sites of these proteins are conserved, and the host range of Det7 includes the P22 and 9NA susceptible Salmonella serovars, despite these phage being morphologically different in tail structure: Det7 has a contractile tail (Myoviridae), P22 has a short tail (Podoviridae), and 9NA has a non-contractile long (Siphoviridae) tail. We hypothesize that each of Det7’s tail spike proteins are responsible for its ability to infect a particular subset of hosts. To investigate this, biochemical and genomic means were used to characterize the structure of the Det7 tail. Genome comparison of related phage in addition to host ranges allows for further characterization of tail spikes and determination of host specificities of tail spike proteins. This project provides insight into the function of these tail proteins and supports the hypothesis of evolution by recombination as the primary mechanism in adaptation of their host ranges.