Date Thesis Awarded


Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)




Helen Murphy

Committee Members

Mark Forsyth

Beverly Sher

Camilla Buchanan


Biofilms are complex, cooperative microbial communities encased in an extracellular matrix and attached to a surface. Biofilms are ubiquitous in virtually all environments and perform many important ecological functions. They can also cause dangerous, drug-resistant infections. There is thus great interest in studying biofilms and how to combat them.

The research presented here uses natural isolates of the budding yeast, Saccharomyces cerevisiae, to explore the fitness effects of biofilm formation. Biofilm-forming and non-biofilm-forming strains were grown alone and in mixed colonies with and without inducing biofilm formation, and the change in biofilm-strain frequency used to determine what conditions favor biofilm-forming strains. It was found that biofilm formation confers a robust fitness advantage when strains are grown in mixed colonies. Images taken of colonies support the hypothesis that this fitness advantage is due to greater spatial use by biofilms.

This research also explores ways to disrupt S. cerevisiae biofilms using natural S. cerevisiae killer toxins. Competition assays were conducted between biofilm-forming and toxin-producing strains. It was found that biofilm-forming strains differ widely in their susceptibility to killer toxins, but that some toxins can greatly interfere with biofilm formation.

Lastly, this research explores the use of engineered "Trojan Horse" toxin-producing strains to achieve biofilm disruption, with mixed success.

Throughout, the research presented here explores the fitness and function of S. cerevisiae biofilm formation as a cooperative phenotype and as a spatial strategy, suggesting new approaches to study and to combat biofilms.

On-Campus Access Only