Abstract
Pseudomonas aeruginosa, an opportunistic pathogen, requires iron for virulence and can obtain this nutrient via the acquisition of heme, an abundant source of iron in the human body. A surplus of either iron or heme can lead to oxidative stress; thus, the Fur (ferric uptake regulator) protein blocks expression of genes required for iron and heme uptake in iron-replete environments. Fur also represses expression of two nearly identical genes encoding the 116- and 114-nucleotide (nt) long PrrF1 and PrrF2 RNAs, respectively. While other Pseudomonads encode for the two PrrF RNAs at separate genomic loci, PrrF1 and PrrF2 are encoded in tandem in all sequenced strains of P. aeruginosa. In this report we characterize a third longer transcript encoded by the prrF locus, PrrH, which is repressed by heme as well as iron. We mapped the PrrH RNA in PA01 using 5′ rapid amplification of cDNA ends (RACE) and northern analysis, demonstrating the PrrH RNA is 325 nt in length. Accordingly, transcription of PrrH initiates at the 5′ end of prrF1, proceeds through the prrF1 terminator and prrF1-prrF2 intergenic sequence (95 nt), and terminates at the 3′ end of the prrF2 gene. We also present evidence that repression of PrrH by heme causes increased expression of previously identified PrrF-regulated genes, as well as newly identified iron- and heme-activated genes. Thus, the PrrH RNA appears to impart a novel heme regulatory mechanism to P. aeruginosa.
Highlights
Pseudomonas aeruginosa is a gram-negative opportunistic pathogen that causes serious infections in immuno-compromised individuals, such as burn victims and cancer patients, as well as persons with cystic fibrosis (CF)
The location of the riboprobe used for previous RNase protection assay (RPA) analysis explains the apparent discrepancy in size estimation of this longer transcript: the distance from the PrrF1 transcriptional start site to the 59 end of the RPA riboprobe is 183 nt (Figure 2C), just one nucleotide difference in length from what was previously reported to be the size of the longer transcript. It appears that this longer RNA is generated when transcription of PrrF1 continues through its Rho-independent terminator, extends through the prrF1-prrF2 intergenic region (95 nt), and ends at the prrF2 Rho-independent terminator (Figure 2C). These results indicate that the long PrrF transcript previously identified by RPA is 325 nucleotides in length and spans the entire prrF locus of P. aeruginosa (Figure 2C)
Heme acquisition plays an important role in pathogenesis for several bacteria and is hypothesized to confer a similar advantage to P. aeruginosa during infection
Summary
Pseudomonas aeruginosa is a gram-negative opportunistic pathogen that causes serious infections in immuno-compromised individuals, such as burn victims and cancer patients, as well as persons with cystic fibrosis (CF). Iron in its ferrous form is freely diffusible through the outer membrane and transported into the cytoplasm by inner membrane transport systems. The insolubility of ferric iron in aerobic environments, limits accessibility to this nutrient, and the sequestration of iron by host proteins from potential pathogens creates a substantial barrier to infection. To scavenge insoluble or host-bound iron, many bacteria use siderophores, low molecular weight iron-chelating compounds. Ferri-siderophore complexes are bound at the cell surface by specific outer membrane receptors and transported into the periplasm, where a periplasmic binding protein delivers the complex to an inner membrane transporter [5]. The siderophore is degraded, releasing the iron for use in a multitude of cellular processes including respiration, gene regulation, and environmental sensing [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
