This ferredoxin domain substitutes the portion of colicin M required for receptor binding and translocation, presumably fulfilling this role by parasitizing an existing ferredoxin-based

iron acquisition pathway. The ability of susceptible strains of Pectobacterium to utilize plant ferredoxin as an iron source was also demonstrated, providing additional evidence for the existence of such a system. If this hypothesis is correct, it represents the first example of iron piracy directly from a host protein by a phytopathogen and serves as a testament of the flexibility of evolution in creating new bacteriocin specificities. Iron is essential for most life due to its role as a cofactor in the transport and storage of oxygen and in numerous redox reactions buy INK 128 (Lindley, 1996). While abundant, iron is effectively insoluble under aerobic conditions making it the limiting nutrient for microbial life in many environments (Krieg et al., 2009). To overcome this obstacle and to obtain iron in a form available for growth, bacteria produce and secrete a diversity of molecules with strong affinity for ferric iron (Fe3+) or iron-containing compounds. These molecules range in size from small organic acids (citrate) to larger siderophores (catecholate) and proteins (haemophores; Ratledge & Dover, 2000). In Gram-negative bacteria, the outer

membrane serves as a permeability barrier protecting the cell from antibiotics, detergents and cell-wall-degrading enzymes Montelukast Sodium (Delcour, 2009). However, the outer membrane bilayer also serves as a barrier STA-9090 to the uptake of iron-scavenging compounds and as such it contains a conserved family of β-barrel receptors (TonB-dependent receptors), which selectively transport iron and other nutrient-containing compounds using energy derived from the proton motive force, through interaction with the TonB–ExbB–ExbD

complex (Pawelek et al., 2006). Some bacteria also produce receptors for the import of noncognate siderophores (xenosiderophores), providing an advantage to the microorganisms in a mixed community where the vast majority of soluble iron exists in a siderophore complex (Jurkevitch et al., 1992; Greenwald et al., 2009). The availability of iron can also be a deciding factor in the success or failure of bacterial infection, and consequently, mammalian hosts restrict the availability of iron through the production of iron-binding proteins, transferrin, lactoferrin, haemoglobin and ferritin. Siderophores produced by some pathogens bind iron with ultra-high affinity and so are able to scavenge iron directly from host-binding proteins (Weinberg, 2009). Other bacteria acquire iron directly from these host proteins, either through binding to a cell surface receptor or through the production and secretion of binding proteins (Cornelissen & Sparling, 1994).