Honors Theses and Capstones

Date of Award

Spring 2011

Project Type

Senior Honors Thesis

College or School



Molecular, Cellular and Biomedical Sciences

Program or Major


Degree Name

Bachelor of Science

First Advisor

Vaughn Cooper


Biofilm populations are known to harbor great diversity, but the importance of this diversity is not fully understood. A likely contributor to this variation is the second messenger molecule cyclic-di-GMP: low levels associate with a planktonic lifestyle while high levels favor biofilm formation. In ongoing studies of an evolving biofilm population of Pseudomonas aeruginosa (PA), we observed extensive ecological diversification that may relate to this lifestyle switch. In PA, the gene bifA encodes a phosphodiesterase that is known to degrade cyclic-di-GMP and reduce biofilm. This gene was cloned onto a plasmid under control of an inducible promoter and the plasmid was added to each of seven different members of a diverse biofilm community. We also constructed communities lacking a single member. The fitness of each biofilm community, with a single member expressing bifA, lacking a member, or unaltered, was then quantified. Reductions in community fitness were observed when a single genotype expressed bifA and hence experienced low levels of cyclic-di-GMP. This result demonstrates that this messenger molecule regulates the biofilm lifestyle at the population level as well as the individual level. Subtraction of individual community members produced varied effects on fitness that associated with their ecological role. Together these results suggest that the synergy of diverse biofilms depends on a balance of genotypes varying in their regulation of molecules that define their niches.