A novel siderophore system is essential for the growth of Pseudomonas aeruginosa in airway mucus

Abstract

Pseudomonas aeruginosa establishes airway infections in Cystic Fibrosis patients. Here, we investigate the molecular interactions between P. aeruginosa and airway mucus secretions (AMS) derived from the primary cultures of normal human tracheal epithelial (NHTE) cells. PAO1, a prototype strain of P. aeruginosa, was capable of proliferating during incubation with AMS, while all other tested bacterial species perished. A PAO1 mutant lacking PA4834 gene became susceptible to AMS treatment. The ΔPA4834 mutant was grown in AMS supplemented with 100 μM ferric iron, suggesting that the PA4834 gene product is involved in iron metabolism. Consistently, intracellular iron content was decreased in the mutant, but not in PAO1 after the AMS treatment. Importantly, a PAO1 mutant unable to produce both pyoverdine and pyochelin remained viable, suggesting that these two major siderophore molecules are dispensable for maintaining viability during incubation with AMS. The ΔPA4834 mutant was regrown in AMS amended with 100 μM nicotianamine, a phytosiderophore whose production is predicted to be mediated by the PA4836 gene. Infectivity of the ΔPA4834 mutant was also significantly compromised in vivo. Together, our results identify a genetic element encoding a novel iron acquisition system that plays a previously undiscovered role in P. aeruginosa airway infection.

Role of Iron Uptake Systems in Pseudomonas aeruginosa Virulence and Airway Infection

“…Whether PA5248 accounts for the retained ability of a P. aeruginosa feoB mutant under low-oxygen reducing conditions remains to be established. Very recently, a novel putative siderophore system which plays important roles in P. aeruginosa viability in vitro in airway mucus secretions and in infectivity in burn wound and airway infection mouse models was identified (76), supporting the hypothesis that still unexplored iron uptake functions may be encoded by the P. aeruginosa genome.…”

Chalkophores

“…It is not yet clear what the primary role of this metallophore is in S. aureus or how a broad-spectrum metallophore is regulated in different environments. Staphylopine-like operons are found in other pathogenic species, including P. aeruginosa , in which the products of those genes are needed for growth within the host environment (188). Pseudopaline, the opine metallophore produced by these staphylopine-like operons, has recently been identified, and evidence that it plays a role in zinc and nickel import is available (189–191).…”

Biosynthesis of an Opine Metallophore by Pseudomonas aeruginosa

“…In addition, transport mutants (Δ Pa4834 ) show significantly attenuated growth in murine airway and burn wound infection models. 12 Taken together, these data suggest that P. aeruginosa may be producing a metallophore similar to staphylopine and that this metallophore plays an important role in pathogenesis, which is surprising given the expanse of evolution separating the two species. We hypothesized that PaNAS would produce a nicotianamine product using SAM exclusively or in concert with an amino acid substrate (unknown #1, Figure 2B) and that PaODH would act on the NAS product by incorporating an α -keto acid (unknown #2, Figure 2B).…”

“…Homologous operons are found in Serratia marcescens (WW4) and Yersenia pestis (CO92), suggesting that opine metallophores are produced by these pathogens. Gi et al 12 predicted the presence of NAS in the P. aeruginosa operon. Their work demonstrates that the operon is involved in iron uptake during growth in culture derived airway mucus.…”