Characterizing the Effect of Quorum Sensing on Aggregation and Virulence in Pseudomonas aeruginosa

Abstract

Quorum sensing (QS) is a cell-to-cell communication process performed by bacteria, including human pathogen Pseudomonas aeruginosa, to coordinate the expression of virulence genes through the secretion and reception of a common signal molecule, termed an autoinducer. In addition to the characterized P. aeruginosa specific QS signaling pathways, surprisingly, both virulence factor expression and biofilm formation in P. aeruginosa have been reported to be regulated by a “universal” autoinducer called AI-2 through an unknown mechanism. While P. aeruginosa has not been reported to produce AI-2, this universal autoinducer is synthesized by hundreds of species of bacteria and is often associated with chemotaxis and biofilm formation. To experimentally determine AI-2’s effect on P. aeruginosa’s aggregation and virulence, brightfield imaging was used to visualize aggregate formation with varying concentrations of AI-2. Additionally, to investigate the influence of specific chemotaxis genes on aggregation, PAO1 mutagenesis was utilized to generate the P. aeruginosa mutants ΔcheY and Δpsl. Brightfield and stain-based florescence imaging were then used to quantify the aggregation phenotype of each mutant. While AI-2 was shown to have no observable influence on P. aeruginosa aggregation, the knockout mutant aggregation quantification assays showed that the quorum sensing and chemotaxis systems have clear relevance. While AI-2 may not be a novel therapeutic for Cystic Fibrosis patients with chronic Pseudomonas aeruginosa infections, there still exists the potential for other mechanisms of aggregate formation and dispersal to overlap with QS and be targeted therapeutically in the future.