Mechanisms of nitric oxide-mediated biofilm dispersal in Pseudomonas aeruginosa

The biological signal molecule nitric oxide (NO) was found to induce biofilm dispersal across a range of bacterial species including Pseudomonas aeruginosa, which led to its consideration for therapeutic strategies to treat biofilms and biofilm-related infections. However, despite the clear link between NO and the bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP), a secondary messenger molecule in bacteria that controls the transition between planktonic cells and biofilms, the direct NO sensor that can transmit NO signal into intracellular changes and c-di-GMP levels has not been fully elucidated in P. aeruginosa. It has also been observed that biofilms are often not completely dispersed after exposure to NO and multiple-doses of NO do not improve biofilm dispersal. To better understand those phenomena, to identify putative NO binding receptors and to elucidate the molecular pathway of NO induced dispersal, this study has successfully created transcriptomic profiles of both messenger RNA and small, non-coding RNA in P. aeruginosa untreated planktonic cells and biofilms as well as the cells remain within biofilms after NO treatment and NO dispersed cells. Based on the RNA-Seq data, this study has highlighted several new targets that may be involved in NO induced dispersal. Moreover, this research has linked two important environmental signals (iron and NO) with their roles in biofilm development. Furthermore, it was found that the transcriptional factor FhpR can sense NO to trigger production of the NO binding protein, flavohemoglobin Fhp, which was linked to incomplete biofilm dispersal. Overall, work presented in this thesis has addressed the mechanisms of NO induced biofilm dispersal in P. aeruginosa and offered new perspectives for improving the use of NO in biofilm control strategies via using imidazole to inhibit Fhp and using iron chelators to control iron concentrations in the environment.Doctor of Philosoph