Date on Senior Honors Thesis


Document Type

Senior Honors Thesis

Degree Name




Author's Keywords

Evolution; Virulence; Pseudomonas; Drosophila; Infection


Evolution is the process by which species change their genetic traits, such as the pathogenicity of bacteria, over time in response to changes in their environment. Although the genetic mechanisms underlying many evolutionary processes have been revealed, it is still not well understood how opportunistic pathogens, such as Pseudomonas aeruginosa, become virulent. The overall goal of this thesis is to test the Coincidental Evolution Hypothesis, which proposes that the virulence of opportunistic pathogens evolves coincidentally as a by-product of their interaction with their natural predators. I hypothesized that the virulence of ancestral Pseudomonas aeruginosa changes over time if it co-evolves with its natural predator, the amoeba. Specifically, I predicted that evolved Pseudomonas aeruginosa becomes more virulent to survive against the amoeba. To test this hypothesis, I infected Drosophila, the fruit fly, as an alternative host to humans with ancestral and evolved Pseudomonas aeruginosa. Survival analysis showed that the evolved strain of Pseudomonas aeruginosa was more virulent than the ancestral strain. This provides insights into how opportunistic pathogens might evolve and could eventually be used in pharmaceutical research to combat bacterial antibiotic resistance.

Lay Summary

Evolution of bacteria occurs very rapidly. With opportunistic pathogens (organisms that do not need to be a pathogen to survive, but can be in certain environments), not much is known with how they evolve with respect to virulence. Using two different types of Pseudomonas aeruginosa (a type of opportunistic bacteria) that are either "unevolved" or "evolved", the goal of this experiment was to see if they had different virulences when in the host Drosophila melanogaster (fruit fly).