Pseudomonas aeruginosa biofilm formation, structure, and matrix composition

Abstract

The vast majority of microbial life exists in biofilm communities. Biofilms are microbial aggregates encased within an extracellular matrix comprised of exopolysaccharides (EPS), proteins, lipids, and other biopolymers. Pseudomonas aeruginosa is a gram-negative opportunistic pathogen that is particularly adept at forming biofilms. P. aeruginosa establishes chronic infections in niches including chronic wounds, medical implants, and the airways of cystic fibrosis patients due in large part to the formation of biofilms. Growth in biofilms affords the bacterial community benefits such as increased antibiotic tolerance and heightened protection against host immune clearance. The P. aeruginosa biofilm matrix can contain three different EPS: Psl, Pel, and alginate, as well as DNA, lipids, and structural and protective matrix proteins. Depending on the environmental niche, P. aeruginosa can draw from the plethora of biofilm matrix components at its disposal in order to most aptly structure and functionalize its matrix. In this dissertation I describe a unique mode of P. aeruginosa biofilm development which relies solely upon calcium-alginate cross-linking to achieve structural stability. I also identify multiple alginate-associating matrix proteins and characterize catalase (KatA) as a matrix-associated protein important to the biofilm community. Lastly, I present observations detailing the impact of calcium on Psl production as well as a novel bioorthogonal method for metabolically labeling P. aeruginosa alginate. Together, these findings contribute valuable insight into the structure and functionalization of the biofilm matrix of P. aeruginosa.