Impact of Siderophore Production on Pseudomonas aeruginosa Infections in Immunosuppressed Mice

Abstract

Pseudomonas aeruginosa produces siderophores, pyoverdin and pyochelin, for high-affinity iron uptake. To investigate their contribution to P. aeruginosa infections, we constructed allelic exchange mutants from strain PAO1 which were deficient in producing one or both of the siderophores. When inoculated into the calf muscles of immunosuppressed mice, pyochelin-deficient and pyoverdin-deficient mutants grew and killed the animals as efficiently as PAO1. In contrast, the pyochelin-and pyoverdin-deficient (double) mutant did not show lethal virulence, although it did infect the muscles. On the other hand, when inoculated intranasally, all mutants grew in the lungs and killed immunosuppressed mice. Compared with PAO1, however, the pyoverdin-deficient mutant and the double mutant grew poorly in the lungs, and the latter was significantly attenuated for virulence. Irrespective of the inoculation route, the pyoverdin-deficient and doubly deficient mutants detected in the blood were significantly less numerous than PAO1. Additionally, in vitro examination demonstrated that the growth of the double mutant was extremely reduced under a free-iron-restricted condition with apotransferrin but that the growth reduction was completely canceled by supplementation with hemoglobin as a heme source. These results suggest that both pyoverdin and pyochelin are required for efficient bacterial growth and full expression of virulence in P. aeruginosa infection, although pyoverdin may be comparatively more important for bacterial growth and dissemination. However, the siderophores were not always required for infection. It is possible that non-siderophore-mediated iron acquisition, such as via heme uptake, might also play an important role in P. aeruginosa infections.

Interspecies competition triggers virulence and mutability in Candida albicans–Pseudomonas aeruginosa mixed biofilms

“…Because the levels of free ferric iron in biological systems are always extremely low (10 À 8 M), siderophores have an important role in microbe-microbe and host-pathogen interactions (Ratledge and Dover, 2000;Harrison et al, 2008). For example, P. aeruginosa mutants incapable of either siderophore synthesis or siderophore transport are far less virulent than their wild-type counterparts (Takase et al, 2000). In the context of microbial interactions, iron competition in Pseudomonas has been studied, and the role of the pyoverdine siderophore produced by Pseudomonas species has been clearly demonstrated in competition with fungus and bacteria (Loper and Buyer, 1991;Harrison et al, 2008).…”

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

“…CF pathogens have developed mechanisms that enable them to acquire iron from host iron-binding proteins during infection. P. aeruginosa pyoverdine and pyochelin can displace iron from transferrin (Takase et al, 2000). P. aeruginosa also has the ability to release iron from transferrin using elastase (LasB; Wolz et al, 1994), the alkaline protease AprA (Kim et al, 2006) and the endoprotease PrpL (Wilderman et al, 2001).…”

“…Three structurally different pyoverdines have been identified (Briskot et al, 1986) and are the subject of a recent review (Cézard et al, 2015). Pyoverdine plays a role in Pseudomonas pathogenesis in animal models of infection (Meyer et al, 1996;Takase et al, 2000;Xiong et al, 2000). Of particular relevance to CF lung disease is the established role of this siderophore in P. aeruginosa biofilm formation (Banin et al, 2005).…”

Siderophore-mediated signaling regulates virulence factor production in Pseudomonas aeruginosa

“…P. aeruginosa secretes two siderophores, pyoverdine and pyochelin, and mutants that are unable to synthesize pyoverdine have a greatly reduced ability to cause disease in animal models (14,15). Expression of genes required for pyoverdine synthesis is directed by an alternative sigma factor, PvdS (16,17).…”