Date of Award

Summer 5-26-2022

Document Type

Thesis (Ph.D.)

Department or Program

Ecology, Evolution, Environment and Society

First Advisor

Carey D. Nadell

Second Advisor

Deborah A. Hogan

Third Advisor

Mark A. McPeek


Biofilms are communities of microorganisms attached to surfaces through various self-secreted matrix materials. Biofilms are dynamic communities with extensive interactions between their residents. Microorganisms compete, cooperate, and communicate with each other in biofilms. These ecological interactions determine the emergence or loss of strains/species and are critical in the formation and proliferation of biofilms. Furthermore, most natural biofilms are formed by multiple microbial species and strains and these interactions within the biofilm dramatically influence community composition and structure over time. Microbial interactions also influence clinically relevant outcomes such as antibiotic resistance and host virulence. In this thesis we explore the potential interactions of microbial populations with their environment, different strains and species using a combination of molecular techniques, microfluidics, and confocal microscopy. In the first study we explored surface competition and biofilm invasion strategies of two strains of Pseudomonas aeruginosa. We found that different extracellular matrix composition and biofilm production strategies effect their direct competition. One strain was able to outcompete the later during early colonization and growth. In contrast the later strain was able to better invade existing biofilms and more inclined to stay during starvation conditions. This sheds light on the advantages of different colonization strategies and their advantages in diverse environmental settings. In the second project, we explored the effect of nutrition on Candida albicans biofilms by growing them in different media. We studied C. albicans biofilm characteristics in three distinct nutritional niches and found that biofilm architecture and properties were distinct in each nutritional niche. This study highlights the importance of nutrient media, and the effects metabolism has on biofilm formation. Finally, in the last project we studied the interaction of Pseudomonas aeruginosa and Candida albicans in a Cystic Fibrosis (CF) lung environment. We found an increase in biovolume for both species and this result was specific to the biofilm environment. Although we could not identify the mechanism of action, we saw this robust result of increase of biovolume in dual species biofilms across multiple mutants and CF isolates. These studies showcase the importance of microbial ecology in understanding biofilm properties and characteristics.