Siderophore-mediated signaling regulates virulence factor production in Pseudomonas aeruginosa

Abstract

Numerous bacteria secrete low molecular weight compounds termed siderophores that have a high affinity for iron ions. Siderophores have a well-documented role as iron-scavenging chemicals, chelating iron ions in the environment whereupon the ferrisiderophores reenter the bacterial cells by means of specific cell-surface receptors. The iron is then released for incorporation into bacterial proteins. Here we show that in addition to its role as an iron-scavenger, the siderophore pyoverdine that is secreted by Pseudomonas aeruginosa regulates the production of at least three virulence factors (exotoxin A, an endoprotease, and pyoverdine itself), which are major contributors to the ability of this bacterium to cause disease. Regulation occurs through a transmembrane signaling system that includes an outer membrane receptor for ferripyoverdine, a signal-transducing protein that is predicted to extend from the periplasm into the cytoplasm, and a sigma factor. Expression of genes that form part of the regulon is triggered by pyoverdine so that this siderophore acts as a signaling molecule to control the production of secreted products. Recognition that a siderophore acts as a signaling molecule has important implications for the understanding of interactions between bacterial cells.

Pumping iron to keep fit: modulation of siderophore secretion helps efficient aromatic utilization in Pseudomonas putida KT2440

“…This observation can be explained in terms of the self-regulatory nature of pyoverdine. In the case of the mutant, unlike in the wild-type, exogenous pyoverdine addition cannot induce autochthonous siderophore secretion because the mutant does not have the cellular machinery for siderophore synthesis (Lamont et al, 2002;Visca et al, 2007). Thus, its iron uptake would be limited to the extent permitted by the pyoverdine supplied externally.…”

“…Most of the enzymes involved in the ring-opening pathway are iron-dependent oxygenases that require a plentiful iron supply for optimum functioning (Dinkla & Janssen, 2003;Dinkla et al, 2001;Gibson & Parales, 2000). Considering the fact that only a small amount of free iron is available under physiological conditions, owing to its minuscule solubility at physiological pH, one can expect iron to be a limiting factor for microbial growth and proliferation (Lamont et al, 2002). This leads to a paradoxical situation, which has been reported in rhizospheric environments, where iron deficiency has been shown to induce aromatic secretion by plants, but utilization of those aromatics by rhizospheric micro-organisms including P. putida requires iron (Jin et al, 2007(Jin et al, , 2008(Jin et al, , 2010.…”

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

“…Iron-regulated virulence factors of P. aeruginosa are overexpressed in mixed biofilms Lamont et al (2002) demonstrated that in addition to its role as an iron scavenger, the siderophore pyoverdine acts as a signaling molecule to control the production of at least three virulence factors (exotoxin A, an endoprotease and pyoverdine itself) that are major contributors to the ability of P. aeruginosa to cause disease. As pyoverdine production was increased in the mixed biofilms (Figure 4a), we hypothesized that the bacterium shows increased virulence when competing for iron with the fungus.…”

Phage selection for bacterial cheats leads to population decline

“…the production of exotoxins and endoproteases [51], and biofilms [52]). Further research is needed to elucidate the complex interrelationships between putative social and other life-history traits.…”