Mechanistic understanding of cerium oxide nanoparticle-mediated biofilm formation in Pseudomonas aeruginosa

In this study, the biofilm formation of Pseudomonas aeruginosa in the presence of cerium oxide nanoparticles (CeO2 NPs) was investigated. With the addition of 0.1 mg/L and 1 mg/L CeO2 NPs, the biofilm development was substantially enhanced. During the attachment process, the enhanced surface hydrophobicity and excess production of mannosan and rhamnolipids in CeO2 NP treatments were detected, which were conductive to the colonization of bacterial cells. During the maturation period, the biofilm biomass was accelerated by the improved aggregation percentage as well as the secretion of extracellular DNA and pyocyanin. The reactive oxygen species (ROS) generated by CeO2 NPs were found to activate the N-butyryl homoserine lactone (C4-HSL) and quinolone signals secreted by Pseudomonas aeruginosa. Moreover, the quorum sensing (QS) systems of rhl and pqs were initiated, reflected by the stimulated expression levels of biofilm formation-related genes rhlI-rhlR, rhlAB, and pqsR-pqsA. The addition of a quorum quencher, furanone C-30, significantly declined the activities of QS-controlled catalase and superoxide dismutase. A dose of antioxidant, ascorbic acid, effectively relieved the accelerating effects of NPs on biofilm formation. These results indicated that CeO2 NPs could accelerate biofilm formation through the interference of QS system by generating ROS, which provides possible targets for controlling biofilm growth in the NP exposure environments.