Regulation of Pseudomonas aeruginosa biofilm structural integrity by the matrix protein CdrA

Fellow: Courtney Reichhardt, PhD

Mentor:  Matthew Parsek, PhD
Professor, Microbiology

Most bacteria assemble and persist as biofilms, which are multicellular communities encased in a biopolymerrich matrix. In the human host, biofilms often confer resistance to antibiotics and contribute to serious and chronic infections including lung infections in patients with cystic fibrosis (CF). In particular, Pseudomonas aeruginosa is implicated in the majority of lung infections in adult patients with CF. The formidable survival traits of biofilms combined with our dwindling pipeline of effective antibiotics make it imperative that we undertake in-depth analyses to improve our understanding of biofilms. Biofilms form three-dimensional structures that are robust enough to resist clearance by the immune system and medical treatment but also can readily disassemble to allow bacteria to infect new sites. Many questions of how bacteria and matrix molecules interact to form these structures remain unanswered. This proposed research will investigate the maintenance and regulation of P. aeruginosa biofilm structural integrity with a specific focus on a key biofilm matrix protein called CdrA. CdrA was the first biofilm matrix protein discovered in P. aeruginosa, and it has been shown to contribute to biofilm stability. The hypothesis is that CdrA acts in part by serving as a tether between cells and the biofilm matrix that can be cut to initiate biofilm dispersal. Both microbiological and biophysical techniques will be used to broadly test the role of CdrA in biofilm formation, and to investigate the roles of several predicted structural features of CdrA that likely are responsible for its role in the biofilm. Specifically, this hypothesis will be tested with two aims: (1) to examine the localization and functionality of CdrA and its cleavage products within P. aeruginosa biofilms using immunoblots, electron microscopy, and immunofluorescence; and (2) to investigate the structural motifs of CdrA that mediate its interactions with other biofilm matrix constituents as well as biotic surfaces such as respiratory epithelial cells using solid-state nuclear magnetic resonance (NMR), complementary bacterial genetics approaches, and CF host-molecule binding assays. The rationale for this research is that this improved understanding could provide a mechanism to control or treat biofilm-involved infections including CF lung infections. Furthermore, I seek to improve my knowledge and experimental skill-set of microbiology and biofilms in order to become a leader in biofilm and CF research, and to answer important questions about biofilm structure, function, and regulation that likely will rely upon a multidisciplinary approach.