Symbioses are drivers of adaptation. This is particularly clear in bacteria, where rapid evolutionary timescales and smaller genomes make bacteria a clear model system in which to study general rules of evolution and adaptation between symbiotic partners. One such symbiotic partnership is found between bacteria and temperate viruses. Upon infection of bacteria, temperate viruses choose one of two outcomes through tightly regulated molecular feedback loops: lysis (horizontal transmission of the virus through rapid viral replication that results in bacterial cell death), or lysogeny (vertical transmission of the viral genetic material via insertion of its genome into the bacterial chromosome to be replicated with the bacterium). Although viral infection of bacteria usually results in lysis, about 60-75% of all sequenced bacteria are lysogens. The forces that maintain this large-scale infection, and their consequences on bacterial evolution, are largely unknown. GEMS trainee Laura Suttenfield will characterize symbiotic interactions of one such virus-host pair in the human-associated bacterium Pseudomonas aeruginosa and its virus DMS3. This project will examine how evolution of the virus during vertical transmission affects the stability of the lysogen as a whole.