The Roles of OprF in Pseudomonas aeruginosa Biofilms

Many bacteria form multicellular communities known as biofilms. Biofilms contain bacterial cells and a protective extracellular biofilm matrix. This matrix contains exopolysaccharides, extracellular DNA (eDNA), membrane vesicles, and proteins. The matrix proteins are far less characterized than other extracellular biofilm components. In biofilms formed by the model organism Pseudomonas aeruginosa, the protein OprF is abundant in the cellular outer membrane and the extracellular matrix. In my dissertation research, I have presented data supporting the hypothesis that the OprF protein significantly affects P. aeruginosa biofilms. By examining various strain backgrounds and the nutrient-dependent effects of glucose and sodium chloride, I demonstrate that the roles of OprF are condition-dependent. Furthermore, the data confirm that these effects are not due to OprF-dependent differences in the number or morphology of cells in P. aeruginosa biofilms, nor are the nutrient-dependent effects due to differences in media osmolarity or metal concentrations. The research highlights the impact of the OprF protein on late-stage static biofilms via the loss of eDNA from the biofilm matrix. In contrast, I clarify that levels of the P. aeruginosa exopolysaccharide Psl are unaffected by a loss of OprF, and that OprF-dependent biofilm defects are not affected by Pseudomonas Quinolone Signaling molecules. I hypothesize that OprF is impacting P. aeruginosa biofilm eDNA levels via two possible mechanisms: 1) by retaining eDNA in the matrix, or 2) by affecting intracellular pathways involved in cell lysis, which produces eDNA. Future transcriptomic analysis of P. aeruginosa biofilm cells with and without OprF, for which I have optimized RNA extraction, will help elucidate any intracellular effects of OprF.