Utilisation of iron from transferrin and lactoferrin by campylobacters

Iron is a nutrient that bacteria need for many essential processes in the cell. As part of the response to infection by bacteria, animals restrict the amount of iron available. In mammals lactoferrin (in mucosal secretions) and transferrin (in serum) tightly bind free iron to restrict its availability. Unfortunately, successful disease-causing bacteria have found ways to grab iron back from the host. The bacterial mechanisms involved in acquiring iron in the host usually consist of a specific pore on the outer surface of the bacterial cell and an associated transport system that makes the iron available inside the cell. The most important food-associated bacterium that infects humans is Campylobacter and as such is responsible for much misery and economic loss in the UK. Campylobacters normally live in the intestine of many animals, notably chickens, where they do not always cause disease. However, when humans eat food contaminated with campylobacters, an highly unpleasant cramping diarrhoea can follow. Food producers strive to minimise the risks of food poisoning for consumers, but if Campylobacter could be eliminated from the intestines of farm animals, particularly chickens, it would have a significant impact on human health by preventing many thousands of cases of food borne disease each year. If control is to be achieved it is important that we better understand how Campylobacter colonises the intestine. Several components of campylobacters that are essential for growth in the intestine are involved in acquiring iron within the host. In our preliminary work, we have identified a system in campylobacters that can grab iron directly from lactoferrin and transferrin to support bacterial growth. This work has identified candidates for the specific pore on the outer surface of the bacterial cell and the associated transport system that moves the iron to the inside of the cell. Our project objectives are to verify the identify of the components of the system and determine the methods by which iron is removed from lactoferrin/transferrin to allow bacterial growth. With a better understanding of the iron acquisition system we will be able to determine if it would be an suitable target for intervention on the farm in order to block growth in the animal gut and reduce food contamination.

The ability to obtain iron via high affinity iron scavenging systems is an important virulence factor for pathogenic microorganisms. Iron acquisition systems are topical and widely studied because during infection pathogens are likely to be in a state of near continual iron deficiency in the face of fierce competition from the normal microbiota and iron limitation by the host. In host tissues iron is tightly bound by the host iron-binding glycoproteins transferrin (Tf) and lactoferrin (Lf); ovotransferrin (oTf) is found in the avian host. At present four iron uptake systems have been identified in Campylobacter jejuni, with the specificity of only two, CfrA/CeuBCD (enterobactin) and ChuABCDZ (haem), having been determined. Our preliminary work has revealed that, contrary to previous reports, C. jejuni can utilise iron from Tf, Lf and oTf. The outer membrane (OM) ligand gated porin Cj0178 and the inner membrane transporter FeoB were implicated in iron acquisition from Tf and Lf. Our hypothesis is that ferri-Lf/-Tf binds to Cj0178 and the removed iron crosses the OM to be transported into the cytoplasm in the ferrous state. The work proposed in this application addresses the nature of the cell surface receptor and mechanism of iron uptake. We will demonstrate that Tf/Lf bind to the campylobacter cell surface and we will determine the component(s) to which these glycoproteins bind. Given our data implicating Cj0178 in the utilisation of ferri-Tf/-Lf, we will examine if Cj0178 acts as a OM receptor and determine if this LGP is involved in iron transfer from Lf/Tf across the OM. The involvement of FeoB suggests that, at some point during uptake, ferric iron is reduced to ferrous iron. We will investigate the role of FeoB, ferric reductase activity and any involvement of ABC transport systems in uptake. Comparative genome analysis indicates some variation in OM porin expression and so we will seek to establish how the mechanism of uptake varies in different strains.