Within-Host Evolution of Pseudomonas aeruginosa Reveals Adaptation toward Iron Acquisition from Hemoglobin

Pseudomonas aeruginosa airway infections are a major cause of mortality and morbidity of cystic fibrosis (CF) patients. In order to persist, P. aeruginosa depends on acquiring iron from its host, and multiple different iron acquisition systems may be active during infection. This includes the pyoverdine siderophore and the Pseudomonas heme utilization (phu) system. While the regulation and mechanisms of several iron-scavenging systems are well described, it is not clear whether such systems are targets for selection during adaptation of P. aeruginosa to the host environment. Here we investigated the within-host evolution of the transmissible P. aeruginosa DK2 lineage. We found positive selection for promoter mutations leading to increased expression of the phu system. By mimicking conditions of the CF airways in vitro, we experimentally demonstrate that increased expression of phuR confers a growth advantage in the presence of hemoglobin, thus suggesting that P. aeruginosa evolves toward iron acquisition from hemoglobin. To rule out that this adaptive trait is specific to the DK2 lineage, we inspected the genomes of additional P. aeruginosa lineages isolated from CF airways and found similar adaptive evolution in two distinct lineages (DK1 and PA clone C). Furthermore, in all three lineages, phuR promoter mutations coincided with the loss of pyoverdine production, suggesting that within-host adaptation toward heme utilization is triggered by the loss of pyoverdine production. Targeting heme utilization might therefore be a promising strategy for the treatment of P. aeruginosa infections in CF patients.