Iron Homeostasis in Pseudomonas aeruginosa: Targeting Iron Acquisition and Storage as an Antimicrobial Strategy

Pseudomonas aeruginosa causes a wide array of life-threatening acute and chronic infections in humans. This opportunistic pathogen is metabolically highly versatile and harbors multiple virulence factors that allow infection of essentially any organ of the human body. The high capacity of this bacterium to acquire iron facilitates its versatility and is considered one of the P. aeruginosa virulence hallmarks. Iron functions as a redox cofactor of enzymes required for vital biological processes and is thus essential for all living organisms. However, in aerobic environments, iron is mainly present in its ferric form, which is insoluble and poorly bioavailable. This problem increases in the human body because, as a reaction to the infection, the host induces a "nutritional immunity" response aiming to reduce the amount of iron available for invading microorganisms. P. aeruginosa contains several mechanisms for iron acquisition including (1) production of siderophores pyoverdine and pyochelin; (2) use of xenosiderophores produced by other microorganisms; (3) direct transport of ferrous ions; and (4) utilization of host iron carriers (e.g., heme). However, although essential, iron results toxic when present in excess because it facilitates the production of reactive oxygen species (ROS) that damage bacterial cells. P. aeruginosa contains ferritins and efflux systems for iron withdrawal to avoid excess of this metal. Production of iron acquisition and removal systems is highly regulated to ensure sufficient iron for metabolic needs while preventing its toxicity. This chapter covers the different mechanisms used by P. aeruginosa to maintain iron homeostasis, which is vital for this pathogen to grow and proliferate in the host. We also highlight current strategies to block P. aeruginosa infections by disrupting iron homeostasis.