GOLDSCHMIDT AWARD LECTURE

Evolution of Enhanced Psl Exopolysaccharide Production in Chronic Pseudomonas aeruginosa Cystic Fibrosis Isolates

Holly K. Huse (2012 Goldschmidt Female Graduate Student Scholarship Recipient)

Holly’s mentor is Dr. Marvin Whiteley at the University of Texas at Austin, Department of Molecular Genetics and Microbiology

The Gram-negative bacterium Pseudomonas aeruginosa is a common cause of chronic respiratory infections in individuals with the heritable disease cystic fibrosis (CF). These infections can last for decades, resulting in significant morbidity and mortality. Upon establishment, P. aeruginosa infections are difficult to eradicate because the bacterium is highly persistent. This persistence has been partially attributed to P. aeruginosa’s ability to form robust biofilms. While in vitro biofilm growth is well characterized, genetic traits that evolve in vivo and contribute to biofilm formation are less understood.  Recently we identified 24 P. aeruginosa genes that were differentially expressed in chronic P. aeruginosa CF isolates compared to their isogenic progenitor strains. The goal of this study was to identify the function of these genes with the overlying hypothesis that some of these genes would promote biofilm formation in chronic P. aeruginosa strains. To test this hypothesis, we constructed strains of the laboratory bacterium P. aeruginosa PAO1 that expressed these genes at levels observed in the chronic isolates. One of these genes, phaF (PA5060), results in enhanced biofilm formation when expressed in PAO1. PhaF promotes biofilm formation via up-regulation of Psl, an exopolysaccharide essential for attachment and biofilm maintenance. PhaF regulates Psl post-transcriptionally, and the mechanism of this control is currently under investigation. Finally, we show that Psl production is enhanced in 8 of 10 chronic CF isolates compared to ancestral strains, suggesting that Psl is an important biofilm-promoting factor in vivo.