Roles of the PrrF and PrrH Small RNAs in Iron Homeostasis and Virulence of Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen that requires iron to cause infection, but also must regulate the uptake of iron to avoid iron toxicity. The iron- responsive PrrF1 and PrrF2 small regulatory RNAs (sRNAs) are part of P. aeruginosa's iron regulatory network and negatively affect the expression of at least 50 genes encoding iron-containing proteins. The genes for the PrrF1 and PrrF2 sRNAs are located in tandem in P. aeruginosa, allowing for the expression of a distinct, heme-responsive sRNA named PrrH that appears to regulate genes involved in heme metabolism. Using a combination of growth, mass spectrometry, and gene expression analysis, we show here that the ΔprrF1,2 mutant, which lacks expression of the PrrF and PrrH sRNAs, is defective for both iron and heme homeostasis. We also present a new system for differentiating PrrF and PrrH function in P. aeruginosa. We delineate the role of these sRNAs in cell physiology and virulence, and identify PrrF as the main regulator of growth, iron homeostasis, and virulence in an acute infection model. Moreover, we show that inoculation with a ΔprrF1,2 deletion mutant protects against future challenge with wild type P. aeruginosa. We also show PrrH does not regulate its current putative targets either in vitro or during acute lung infection, but that this sRNA may impact siderophore production. Although PrrH does not play a role in acute infection, PrrH may play a greater role in a chronic infection, as longitudinal CF isolates maintain the ability to express PrrH throughout disease. Combined, these data demonstrate that the prrF-encoded sRNAs are central regulators of P. aeruginosa iron homeostasis and virulence.