New key players in Pseudomonas aeruginosa tobramycin-enhanced biofilm formation

Abstract : Introduction: Biofilms are structured microbial communities that are the leading cause of numerous chronic infections which are difficult to eradicate. Within the lungs of individuals with cystic fibrosis, Pseudomonas aeruginosa causes persistent biofilm infection that is commonly treated with aminoglycoside antibiotics such as tobramycin. However, exposure to sublethal concentrations of the aminoglycoside tobramycin were previously shown to increase biofilm formation by P. aeruginosa. Hypothesis and aims: In the current study, we sought to elucidate potential adaptive mechanisms shaping the tobramycin-enhanced biofilm formation in P. aeruginosa. Methodology: We combined confocal laser scanning microscope analyses, proteomics profiling, gene expression assays and phenotypic studies to unravel P. aeruginosa potential adaptive mechanisms in response to tobramycin exposure during biofilm growth. Results: We show that the modified biofilm architecture is related at least in part to increased extracellular DNA (eDNA) release, most likely as a result of biofilm cell death. Furthermore, the activity of quorum sensing (QS) systems was increased, leading to higher production of QS molecules. We also demonstrate upon tobramycin exposure an increase in expression of the small RNAs PrrF1 and PrrF2, known for promoting 4-hydroxy-2- alkylquinolines production, as well as expression of iron uptake systems. Remarkably, biofilm biovolumes and eDNA relative abundances in pqs and prrF1,F2 mutant strains decrease in the presence of tobramycin. Conclusion: Our findings offer experimental evidences for a potential adaptive mechanism linking PrrF1/F2 sRNAs, QS signaling, biofilm cell death, eDNA release, and tobramycin- enhanced biofilm formation in P. aeruginosa.