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Chapter 33 : Iron Metabolism, Transport, and Regulation
Category: Bacterial Pathogenesis
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This chapter discusses the wealth of knowledge about iron metabolism of Campylobacter by discussing mechanisms of iron transport, iron storage, and iron-responsive regulation of genes involved in iron metabolism. Most of the data discussed in the chapter have been obtained by using Campylobacter jejuni, but the author also discusses about the data obtained for Campylobacter coli; it is thought that the mechanisms involved in iron metabolism are essentially similar in both species. The availability of free iron inside mammalian and avian hosts is extremely limited as a result of the toxicity of iron in combination with oxygen. Ferrous iron is utilized by many bacteria, and in Escherichia coli, the high-affinity ferrous transport system expressed under anaerobic conditions involves two proteins, FeoA and FeoB, and a probable transcriptional regulator, FeoC. Enterobactin, which is produced by members of the mammalian and avian intestinal microbial flora, has the potential of being a significant source of iron to C. jejuni. Genes with homology to fhuABD, which encode the outer membrane receptor and part of the ABC transport system of the E. coli ferrichrome uptake system, have been identified in a set of C. jejuni strains. The other genes belonging to iron metabolism found to be upregulated in the rabbit intestine include those encoding Cj0236c, Cj0722c–Cj0723c, Cj1613c, PanBC, and RpmA. The transcriptomic analysis of genes involved in iron metabolism has highlighted some important connections between iron limitation and C. jejuni metabolism.
Iron transport across the gram-negative cell envelope. (Left) TonB- and ABC-dependent transport pathway. Transport through the high-affinity outer membrane receptor is energized by TonB-mediated transduction of energy from the proton motive force with participation from ExbB and ExbD. Passage across the cytoplasmic membrane involves proteins of an ABC transporter system whose ATPase activity energizes the process. (Right) Ferrous iron uptake pathway. Ferrous iron crosses the outer membrane via a nonspecific porin or after reduction of ferric iron. The inner membrane FeoB containing a G protein domain and cytoplasmic FeoA transport the ferrous iron into the cytoplasm.
Iron transport systems of C. jejuni as determined by comparative genome analysis and experimental data (see text for details). Substrates are shown where known, and systems present in all strains are highlighted.
Overview of pathways involved in generation and inactivation of different forms of reactive oxygen species in C. jejuni, including superoxides (O2 –), hydrogen peroxide (H2O2), and alkyl peroxides (RHO2).
Roles of iron and Fur and PerR regulatory proteins in controlling iron metabolism and oxidative stress resistance in C. jejuni. Arrows indicate connecting pathways.
C. jejuni genes differentially expressed between iron-rich and iron-restricted growth conditions a