fhuAofActinobacillus pleuropneumoniaeEncodes a Ferrichrome Receptor but Is Not Regulated by Iron

Abstract

The swine pathogen Actinobacillus pleuropneumoniae possesses a 75-kDa outer membrane protein (OMP), FhuA, the receptor for ferrichrome, a hydroxamate-type siderophore. Polyclonal serum to FhuA reacted with OMP preparations from 12 serotypes of A. pleuropneumoniae under conditions of iron repletion and restriction. Reverse transcription-PCR confirmed that A. pleuropneumoniae fhuA expression is not upregulated in response to low iron levels. An A. pleuropneumoniae fhuA deletion mutant was generated and showed abolishment of ferrichrome uptake.

Molecular characterization of Haemophilus parasuis ferric hydroxamate uptake (fhu) genes and constitutive expression of the FhuA receptor

“…The presence of fhuCDBA genes clearly supports the concept that H. parasuis strains may count for all the necessary Fhu proteins for capturing iron from siderophores. However, these results disagree with others reported recently in the literature [20] The relative position of the four genes in the H. parasuis Fhu region was identical to that of A. pleuropneumoniae [19], in which the fhuC gene is followed by the fhuD, fhuB and fhuA genes, whereas in E. coli or S. Typhimurium the fhuA is followed by fhuC, fhuD and fhuB [11,18]. The different relative position of the four genes in H. parasuis and A. pleuropneumoniae, as compared to E. coli and S. Typhimurium fhu genes, might account for the differences in the regulation of the FhuA protein expression observed in the former species.…”

“…These data support the hypothesis that H. parasuis may use ferrichrome as a source of iron. Our observations are in agreement with the data reported by other authors who claim that ferrichrome is capable to promote the growth and survival of H. parasuis serotype 5 [9] and A. pleuropneumoniae [20] under iron-limiting conditions.…”

“…Its expression was constitutive and therefore independent of the iron concentration available in the culture medium. These results were in agreement with those reported for A. pleuropneumoniae FhuA protein [20]. Moreover, H. parasuis-infected pigs developed a humoral immune response against H. parasuis FhuA protein as we demonstrated by immunoblotting, indicating that the extracellular loops of this protein are exposed to the immune system during the course of infection.…”

Real-Time Quantitative Reverse Transcription-PCR Analysis of Expression Stability ofActinobacillus pleuropneumoniaeHousekeeping Genes during In Vitro Growth under Iron-Depleted Conditions

“…A previous study found that regulation of the ferrichrome receptor, encoded by fhuA, is independent of the iron supply (15). In this investigation, the mean expression of the fhuD gene, which belongs to the same operon as fhuA, was found to be up-regulated twofold in response to low iron levels.…”

“…Another A. pleuropneumoniae iron transport system, via ferrichrome, was represented in the analysis by a gene coding for ferric hydroxamate uptake protein (fhuD), which is part of the fhuCDBA operon (14). Previous results indicated that the regulation of fhuA appears to be independent of the iron supply (15).…”