Role of quorum sensing in UVA-induced biofilm formation in Pseudomonas aeruginosa

Pseudomonas aeruginosa, a versatile bacterium present in terrestrial and aquatic environments and a relevant opportunistic human pathogen, is largely known for the production of robust biofilms. The unique properties of these structures complicate biofilm eradication, because they make the biofilms very resistant to diverse antibacterial agents. Biofilm development and establishment is a complex process regulated by multiple regulatory genetic systems, among them is quorum sensing (QS), a mechanism employed by bacteria to regulate gene transcription in response to population density. In addition, environmental factors such as UVA radiation (400-315 nm) have been linked to biofilm formation. In this work, we further investigate the mechanism underlying the induction of biofilm formation by UVA, analysing the role of QS in this phenomenon. We demonstrate that UVA induces key genes of the Las and Rhl QS systems at the transcriptional level. We also report that pelA and pslA genes, which are essential for biofilm formation and whose transcription depends in part on QS, are significantly induced under UVA exposure. Finally, the results demonstrate that in a relA strain (impaired for ppGpp production), the UVA treatment does not induce biofilm formation or QS genes, suggesting that the increase of biofilm formation due to exposure to UVA in P. aeruginosa could rely on a ppGpp-dependent QS induction.