Iron uptake and quorum sensing in Pseudomonas aeruginosa virulence

Pseudomonas aeruginosa is the main cause of lung function decline among cystic fibrosis (CF) patients. The abundance of regulatory genes in the P. aeruginosa genome is at the basis of the environmental versatility of this bacterium, which is mirrored by its ability to efficiently colonise the CF lung. The CF lung is particularly poor in bio-available iron, and iron depletion is sensed by P. aeruginosa as a primary environmental signal that leads to the expression of virulence genes in the host. P. aeruginosa persists in the CF lung thanks to the expression of iron-uptake systems which are themselves regarded to as virulence factors.Establishment of the P. aeruginosa chronic infection requires the development of a microbial community which evolves into a biofilm. In this microbial community the response of each cell to the environmental stimuli originating from the CF lung is coordinated with that of the other cells. The group-behaviour of P. aeruginosa is primarily controlled by the quorum sensing (QS) system that controls the expression of several virulence genes.The first year of the research project has been aimed at identifying and characterizing key molecular factors involved in iron uptake and QS, in order to identify suitable targets for new-drugs development.We have i characterized the CysB protein, a novel transcription factor involved in the regulation of iron uptake and, likely, virulence genes,. Moreover, by mens of a proteomic approach, we have identified about 200 proteins present in P. aeruginosa periplasm, including factors likely involved in iron uptake.Concerning QS regulation, we have showed, by transcriptome analysis, that the RsaL protein is a global regulator controlling hundreds of P. aeruginosa genes, including QS genes and genes involved in virulence. Functional studies have showed that RsaL on one hand plays a positive role in biofilm production and on the other hand maintains the production of important virulence factors within profitable limits. These results suggest that RsaL could be important in the chronic CF lung infection, characterized by biofilm formation and low level of virulence factors production.In the second year of the project we will continue the characterization of the above factors and their contribution to the lung infection. In order to identify new putative drug targets, we will also study the interplay between QS and iron uptake circuits.