Identification and Characterization of an Outer Membrane Receptor Gene in <i>Acinetobacter baumannii</i> Required for Utilization of Desferricoprogen, Rhodotorulic Acid, and Desferrioxamine B as Xenosiderophores

Abstract

In this study, we found that Acinetobacter baumannii utilized exogenously supplied desferricoprogen, rhodotorulic acid, and desferrioxamine B for growth under iron-limiting conditions. The ferric uptake regulator (Fur) titration assay method was then successfully applied to select iron-regulated genes in A. baumannii genomic libraries. Part of the nucleotide sequence homologous to Escherichia coli, fhuE, obtained from one of the positive clones allowed us to clone the entire gene, which was named fhuE. The fhuE gene had an amino acid sequence consistent with the N-terminal amino acid sequence of the 76-kDa iron-repressible outer membrane proteins in A. baumannii. Reverse transcription-polymerase chain reaction analysis demonstrated that fhuE mRNA is transcribed under iron-limiting conditions, consistent with the presence of a sequence homologous to the consensus Fur box in the promoter region. Disruption of fhuE resulted in the loss of expression of the 76-kDa protein. In addition, the double disruptant of fhuE and basD, which encodes one of the biosynthetic genes for the cognate siderophore acinetobactin, was unable to grow in the presence of desferricoprogen, rhodotorulic acid or desferrioxamine B. However, growth of the double disruptant was restored by complementation with fhuE, demonstrating that A. baumannii FhuE functions as the receptor common to coprogen, ferric rhodotorulic acid and ferrioxamine B.

In Vitro and In Vivo Antimicrobial Activities of Gallium Nitrate against Multidrug-Resistant Acinetobacter baumannii

“…Here, we exploited iron metabolism as a possible target for antibacterial chemotherapy. A. baumannii possesses several iron uptake systems (3,24), and almost all of these are encoded by genes belonging to the core genome of nosocomial strains (29). Acinetobactin, the most extensively studied A. baumannii siderophore, has the ability to withhold iron from transferrin and lactoferrin (65) and appears to be crucial for A. baumannii to establish infection and kill both G. mellonella and mice (25).…”

“…In cells containing sufficient iron levels, the Fur-Fe(II) complex blocks transcription arising from Fur-controlled promoters, which in turn are transcribed under conditions of iron starvation (33). Iron acquisition from the human host appears to be crucial for A. baumannii pathogenicity, as inferred by the presence in this species of multiple iron-uptake systems (3,24) and the reduced lethality of mutants impaired in acinetobactin siderophore synthesis (25). The importance of iron in host-pathogen interactions led us to investigate the effect of Ga(III) on A. baumannii growth, iron regulation, and virulence.…”

Structure and Function of the PiuA and PirA Siderophore-Drug Receptors from Pseudomonas aeruginosa and Acinetobacter baumannii

“…A. baumannii harbors between 21 and 27 TonB-dependent receptors compared to 35 in P. aeruginosa (26). So far, only FhuE (27) and BauA (28), the receptor for the siderophore acinetobactin (29,30), have been characterized in A. baumannii.…”

Pangenome and immuno-proteomics analysis of Acinetobacter baumannii strains revealed the core peptide vaccine targets

“…It is involved in the directed movement of siderophores (low molecular weight iron chelating substances) into, out of or within a cell, or between cells by means of a transporter. Similarly, FhuE receptor is another outer membrane receptor protein required for the uptake of iron via ferric coprogen and ferric-rhodotorulic acid [ 104 ]. Another core vaccine candidate, peptidyl-prolyl isomerases (PPIs) are ubiquitous proteins and are involved in the cis–trans isomerisation of peptide bonds N-terminal to proline (Pro) residues within polypeptide chains.…”