Pseudomonas aeruginosa Uses Multiple Pathways To Acquire Iron during Chronic Infection in Cystic Fibrosis Lungs

Abstract

dPseudomonas aeruginosa chronically infects the lungs of more than 80% of adult patients with cystic fibrosis (CF) and is a major contributor to the progression of disease pathology. P. aeruginosa requires iron for growth and has multiple iron uptake systems that have been studied in bacteria grown in laboratory culture. The purpose of this research was to determine which of these are active during infection in CF. RNA was extracted from 149 sputum samples obtained from 23 CF patients. Reverse transcription-quantitative real-time PCR (RT-qPCR) was used to measure the expression of P. aeruginosa genes encoding transport systems for the siderophores pyoverdine and pyochelin, for heme, and for ferrous ions. Expression of P. aeruginosa genes could be quantified in 89% of the sputum samples. Expression of genes associated with siderophore-mediated iron uptake was detected in most samples but was at low levels in some samples, indicating that other iron uptake mechanisms are active. Expression of genes encoding heme transport systems was also detected in most samples, indicating that heme uptake occurs during infection in CF. feoB expression was detected in all sputum samples, implying an important role for ferrous ion uptake by P. aeruginosa in CF. Our data show that multiple P. aeruginosa iron uptake mechanisms are active in chronic CF infection and that RT-qPCR of RNA extracted from sputum provides a powerful tool for investigating bacterial physiology during infection in CF.

Iron acquisition in the cystic fibrosis lung and potential for novel therapeutic strategies

“…More recently, Martin et al (2011) showed that although pyoverdine was detectable in most P. aeruginosa infected CF sputa, some sputa were pyoverdine-negative (Martin et al, 2011). Consistent with these findings, Konings et al (2013) subsequently demonstrated using real-time quantitative PCR that genes associated with siderophore-mediated iron acquisition including pyoverdine and pyochelin are expressed at low levels in CF sputum, and both haem and ferrous iron uptake genes were also detected, indicating multiple iron uptake pathways are active but siderophore secretion is downregulated (Konings et al, 2013). This phenomenon was further explored by Andersen et al (2015) in a sequence analysis study which confirmed that in the CF lung environment, many P. aeruginosa strains 'cheat' by no longer producing pyoverdine and instead use pyoverdine produced by co-infecting strains (Andersen et al, 2015).…”

Adaptation of Iron Homeostasis Pathways by a Pseudomonas aeruginosa Pyoverdine Mutant in the Cystic Fibrosis Lung

“…In line with this hypothesis, pyoverdine is present in the sputum of some but not all CF patients (31), and in one study, one-third of P. aeruginosa strains isolated from CF patients had lost the ability to produce pyoverdine (32). Additionally, expression of the genes for pyoverdine biosynthesis by P. aeruginosa growing in the CF lung is variable (33). Moreover, recent genome sequencing analysis of numerous CF isolates demonstrated the highest level of genetic diversity among infecting P. aeruginosa strains to be localized to the pyoverdine synthesis and uptake genes (34).…”

“…In support of this idea, genes encoding the ferrous iron and heme uptake systems are consistently expressed by P. aeruginosa growing in the CF lung (33,35). P. aeruginosa acquires ferrous iron via the Feo system, a G-protein-like transporter of ferrous iron (36)(37)(38)(39), and mediates heme acquisition via at least two systems: Phu (Pseudomonas heme uptake) and Has (heme assimilation system) (40).…”

Enterobacteria secrete an inhibitor of Pseudomonas virulence during clinical bacteriuria

“…To our knowledge, this is the first report of a microbial natural product that is a direct inhibitor of a competing species' siderophore transport system. Multiple studies have implicated the pyochelin siderophore system in virulence (74)(75)(76), including genetic abrogation of pyochelin-mediated iron uptake that diminished P. aeruginosa virulence in murine infection models (53,54). In this context, escherichelin-producing Enterobacteriaceae at colonized devices or mucosal surfaces may prevent P. aeruginosa from progressing to symptomatic infection by chemically inhibiting pyochelin-mediated iron uptake.…”