Haem iron‐transport system in enterohaemorrhagic Escherichia coli O157:H7

Abstract

SummaryIn this study, we identified the iron-transport systems of Escherichia coli O157:H7 strain EDL933. This strain synthesized and transported enterobactin and had a ferric citrate transport system but lacked the ability to produce or use aerobactin. It used haem and haemoglobin, but not transferrin or lactoferrin, as iron sources. We cloned the gene encoding an iron-regulated haem-transport protein and showed that this E. coli haem-utilization gene (chuA) encoded a 69 kDa outer membrane protein that was synthesized in response to iron limitation. Expression of this protein in a laboratory strain of E. coli was sufficient for utilization of haem or haemoglobin as iron sources. Mutation of the chromosomal chuA and tonB genes in E. coli O157:H7 demonstrated that the utilization of haemin and haemoglobin was ChuA-and TonBdependent. Nucleotide sequence analysis of chuA revealed features characteristic of TonB-dependent, Fur-regulated, outer membrane iron-transport proteins. It was highly homologous to the shuA gene of Shigella dysenteriae and less closely related to hemR of Yersinia enterocolitica and hmuR of Yersinia pestis. A conserved Fur box was identified upstream of the chuA gene, and regulation by Fur was confirmed.

Characterization of a yjjQ mutant of avian pathogenic Escherichia coli (APEC)

“…The acquisition of iron is crucial for bacterial survival and infection, since this metal is necessary for a series of cellular functions and the concentration of free iron is exceedingly low in host tissues. Therefore bacteria have developed several strategies to sequestrate this essential element (Perkins-Balding et al, 2004) and iron-acquisition systems have been associated with bacterial virulence especially for bacteria causing septicaemia (Janakiraman & Slauch, 2000;Li et al, 2005;Russo & Johnson, 2000;Schaible & Kaufmann, 2004;Torres & Payne, 1997). One of the downregulated genes, sitA, is part of the four-member sit operon which is included within SPI1 of Salmonella Typhimurium and is believed to be located on a pathogenicity island in Shigella flexneri as well (Runyen-Janecky et al, 2003;Zhou et al, 1999).…”

“…The third protein identified and belonging to this category is ChuA, which is an outer-membrane acceptor involved in haem uptake in a series of bacterial pathogens, e.g. EHEC, UPEC, Neisseria meningitidis and Shigella dysenteriae (Mills & Payne, 1995;Torres & Payne, 1997;Welch et al, 2002). The ability to use haem/haemoglobin as iron source has been implicated as an important determinant of virulence and it is assumed that these compounds provide the requisite amounts of iron necessary for the expression of virulence factors such as haemolysins, proteases or cytolysins (Lee, 1995).…”

“…Among the wildtype-enriched spots, four were found to represent proteins involved in iron uptake (spots 1-4), indicating a notable role of YjjQ in the utilization of this metal (Table 3): SitA is a periplasmic iron-binding protein which is encoded in a four-member operon that mediates manganese and iron transport (Hantke, 2001;Sabri et al, 2006;Zhou et al, 1999). The second downregulated protein, ChuA, is involved in haem uptake in EHEC, UPEC, APEC (Li et al, 2005;Torres & Payne, 1997;Welch et al, 2002) and several other bacterial pathogens. The TonB-dependent outer-membrane protein FyuA is encoded by the ferric yersiniabactin uptake system (Pelludat et al, 1998), and the putative function of IreA is a siderophore receptor associated with ExPEC (Russo et al, 2001).…”

Exploiting the power of OMICS approaches to produceE. coliO157 vaccines

“…15 In support of our analysis, the HP group includes several proteins that we and others have previously identified as important virulence factors of EHEC O157:H7 as well as other proteins not previously identified in virulence but which were consider important immunogens. [18][19][20][21][22][23] Several studies in murine models of EHEC infection have emphasized the importance of mucosal delivery routes as a promising way to induce immune responses offering a combination of protection and blockage of EHEC intestinal colonization, mainly through expression of secretory IgA (sIgA) 24 (Fig. 1).…”

VTEC enteropathogenicity

“…dysenteriae-1, VT-producing E. coli 0157:H7 do not express, and cannot use, aerobactin (Lawlor and Payne 1984;Payne 1989;Struele~s et al 1990;Torres and Payne 1997;Chart unpubhshed). Torres and Payne (1997) showed that E. coli 0157 can use haem and haemoglobin as sources of iron. Haem utilization involves a 69 kDa iron-regulated outer membrane protein, the expression of which is controlled by the Fur locus.…”