Date of Award

Winter 2012

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Vaughn Cooper


In the environment, bacterial populations often exist as communities called biofilms. During this sessile state, bacteria excrete exopolysaccharides that form a sticky, protective matrix. This protective matrix also presents a prominent medical challenge since chronic infections of cystic fibrosis (CF) patients are commonly biofilm associated. Pseudomonas aeruginosa is one bacterium that can colonize the CF lung and persist in a biofilm community. During chronic infections, P. aeruginosa adapts to its lung environment and displays genetic and phenotypic diversification. To model evolution during chronic infections, biofilm populations were experimentally evolved for 540 generations and the genetic variation was sampled at 100, 260 and 540 generations to identify adaptive alleles. Of multiple alleles that fixed within the B1 population, mutations in two genes, ppk and rcsC, were characterized since they were thought to be adaptive. The goal was to measure the fitness effects of these alleles and to identify the mechanisms that explain why they would be adaptive.