For this reason, the expression of iron acquisition genes is tightly regulated. This ATP hydrolysis provides the energy for transport of the ligand across the inner membrane into the cytoplasm ( 10).ДЄlthough iron is essential, high levels of iron are toxic. This system usually consists of two integral membrane proteins, which form the channel, and two hydrophilic proteins with ATPase activity. Following transport into the periplasm, the iron ligand is bound by a specific periplasmic binding protein, which delivers its ligand to an ATP binding cassette (ABC) transport system located in the inner membrane. Energy for transport across the outer membrane requires an active TonB-ExbBD complex ( 40). Heme receptors transport the intact heme moiety into the periplasm, whereas receptors for host iron proteins remove the iron or heme from the protein at the cell surface and only the iron or heme is transported into the cell ( 9, 47, 55). Other receptors recognize specific iron-containing complexes synthesized by their hosts, such as lactoferrin, transferrin, heme, or hemoglobin.

Some of these receptors transport ferrisiderophores, which are small, iron-binding molecules synthesized by microorganisms. Many of these systems involve the synthesis of outer membrane receptors that bind a specific ligand and transport it across the outer membrane. Iron is essential for nearly all life, and gram-negative bacterial pathogens have evolved numerous systems for the acquisition of this element. However, a mutant defective in the vibriobactin, Fbp, and Feo systems was not attenuated in a suckling mouse model, suggesting that at least one other iron transport system can be used in vivo. cholerae strains carrying mutations in one or more of the potential iron transport genes indicated that both Feo and Fbp contribute to iron acquisition. Conversely, ascorbate inhibited transport by the Fbp system, suggesting that it transports ferric iron. flexneri iron transport mutant was stimulated by the reducing agent ascorbate, consistent with Feo functioning as a ferrous transporter. Transport of radioactive iron by the Feo system into the S. Two other ABC transporters were also evaluated but were negative by these assays. Clones encoding either the Feo or the Fbp system exhibited characteristics of iron transporters: both repressed the expression of lacZ cloned under the control of a Fur-regulated promoter in Escherichia coli and also conferred growth on a Shigella flexneri mutant that has a severe defect in iron transport. Previously uncharacterized potential iron transport systems, including a homologue of the ferrous transporter Feo and a periplasmic binding protein-dependent ATP binding cassette (ABC) transport system, termed Fbp, were identified in the V. Strains defective in both of these systems grow well in laboratory media and in the infant mouse intestine, indicating the presence of additional iron acquisition systems. Vibrio cholerae has multiple iron acquisition systems, including TonB-dependent transport of heme and of the catechol siderophore vibriobactin.

Macvector interface