[Journal Club] A study published by Isabelle Schalk and Gaëtan Mislin’s team (UMR7242, University of Strasbourg) reveals how Pseudomonas aeruginosa adapts its iron-acquisition strategy to its environment

Iron is essential for bacterial survival, but it is particularly difficult to access within the host, where it is tightly controlled and often scarce. To acquire this essential nutrient, the opportunistic pathogen Pseudomonas aeruginosa has an extensive arsenal of 21 transport systems located in its outer membrane. Many of these systems rely on siderophores, small molecules that bind iron with high affinity and allow bacteria to acquire it. However, P. aeruginosa does not express all of these systems simultaneously. Instead, it selectively activates the pathways that are most advantageous according to the resources available in its environment. It can even exploit siderophores produced by neighboring microorganisms, through a strategy known as “siderophore piracy.”

In this study, published in PNAS, the team sought to understand how P. aeruginosa detects different catechol-type molecules and uses this information to regulate the expression of transporters involved in iron acquisition. Using fluorescent reporters and mathematical modeling, the researchers quantified the responses of five transporters to different catechol-type siderophores, as well as to host-produced catecholamines such as epinephrine, norepinephrine, and L-DOPA.

The results reveal that these transporters do not all respond in the same way. Some are activated in a switch-like manner once siderophore concentrations reach a specific threshold, whereas others respond progressively over a much broader range of concentrations. The study also shows that iron availability strongly influences these responses, with different transporters displaying distinct patterns of iron-dependent repression. Together, these regulatory mechanisms allow P. aeruginosa to integrate multiple environmental signals and determine which iron-acquisition pathways should be activated under specific conditions.

These findings highlight the remarkable ability of P. aeruginosa to “sense and decode” a diverse range of environmental catechols and to fine-tune its iron-acquisition machinery according to the niche it occupies, whether in a competitive microbial community or within a host. They provide new insights into siderophore piracy and, more broadly, into how Gram-negative bacteria adapt their physiology to iron limitation.
The study also has potential therapeutic implications. Iron-uptake transporters are key entry points for siderophore–antibiotic conjugates such as cefiderocol. Understanding the environmental conditions that control the expression of these transporters may therefore provide valuable insights into the uptake and efficacy of such therapeutic strategies.

Volck F, Revillot-Schmidt AE, Hubert T, Crespin V, Mislin GLA, Cunrath O, Madec M, Schalk IJ. Distinct transcriptional logics of catechol siderophore transporters in Pseudomonas aeruginosa for efficient iron acquisition. Proc Natl Acad Sci U S A. 2026 Aug 18;123(33): e2602150123.
doi: 10.1073/pnas.2602150123. Epub 2026 Aug 14.