Tessa Widmyer

Major: Medical Sciences, Microbiology

Faculty Advisor: Holly Wichman and Craig Miller

Project Title:

Modeling return to virulence of attenuated viruses

Abstract

Vaccines are essential to reduce infectious diseases. One method to create successful vaccines is to use live, attenuated viruses. However, these attenuated viruses may recover virulence with a relatively small number of mutations. The Wichman-Miller lab is researching methods to reliably and safely design vaccines that are resistant to recovery using the bacteriophage ΦX174, a virus that infects bacteria, as a model of viral adaption. This project seeks to answer questions about how combinations of synonymous mutations affect viral fitness and how quickly these mutants can evolve to regain higher fitness. A set of ΦX174 constructs were investigated where three of the constructs had a single mutant gene and the remaining constructs combined these mutant genes into every possible double and triple mutant. Flask passaging was used, growing the phage a generation at a time in liquid culture, to explore how quickly these constructs evolved to increased fitness. Each construct was passaged five times, using the endpoint of each passage to begin the next, and plating after each generation to look at plaque size and calculate the fitness of the passage. An increase in plaque size and corresponding increase in fitness may indicate that evolution occurred during the passage. Results indicate that an increase in fitness was more likely to occur in constructs that combined attenuated genes and had lower starting fitness. Moving forward we plan on using chemostats, which give rise to about 100 generations in 24 hours, to attempt to evolve those constructs that were resistant to change in five passages.