Promote Iron Uptake Research Articles

NRAMP1 promotes iron uptake at the late stage of iron deficiency in poplars.

Iron (Fe) is an essential micronutrient for plant survival and proliferation. Plants have evolved complex mechanisms to maintain Fe homeostasis in response to Fe deficiency. In this study, we evaluated the physiological, biochemical and transcriptomic differences between poplars grown under Fe-sufficient and Fe-deficient conditions to elucidate the mechanistic responses of poplars to Fe deficiency. Our results revealed that chlorophyll synthesis and photosynthesis were inhibited under Fe-deficient conditions. The inhibition of these pathways caused chlorosis and reduced shoot growth. Although both photosynthetic systems (PSI and PSII) were inhibited under Fe limitation, PSI was affected more severely and earlier than PSII. Fe deficiency also promoted root growth and increased the accumulation of divalent metal ions in roots. IRT1 and NRAMP1 are both Fe2+ transporters for iron uptake in Arabidopsis. In this study, however, only NRAMP1 was induced to promote Fe2+ uptake in roots at the late stage of Fe deficiency response. It indicated that NRAMP1, rather than the more well-known IRT1, might be a major Fe2+ transporter at the late stage of Fe-deficiency in poplars.

Effect of duck egg white peptide-ferrous chelate on iron bioavailability in vivo and structure characterization.

In order to utilize the industrial by-product 'salted duck egg white' as novel iron additives, the effects of desalted duck egg white peptides-ferrous chelate (DPs-Fe) on the promotion of iron uptake and the structure were investigated. Different doses of DPs-Fe were given and iron sulfate (FeSO4 ) was used as a positive control. After three weeks, hemoglobin (Hb), hematocrit (HCT), red blood cells (RBCs), mean corpuscular volume (MCV), serum iron (SI) and serum ferritin (SF) in iron-deficiency anemia (IDA) rats could be significantly (P < 0.05) increased to the normal levels by DPs-Fe. The gene expressions of divalent metal transporter 1 (DMT1), ferroportin 1 (FPN1) and Hepcidin could be regulated by DPs-Fe. Additionally, DPs-Fe was formed during the chelation process and the structure was characterized. Eight crucial iron-chelating peptides of duck egg white peptides (DPs) were identified by HPLC-ESI-MS/MS, such as Pro-Val-Glu-Glu and Arg-Ser-Ser. It indicated that Glu, Asp, Lys, His, Ser, Cys residues might play crucial roles in the chelating of DPs with iron. DPs-Fe could be a potential iron supplement, and the Glu, Asp, Lys, His played important roles in binding iron and promoting iron uptake. This research expands the understanding of iron uptake by DPs and provides an opportunity for recycling a discarded processing byproduct. © 2018 Society of Chemical Industry.

Complex Iron Uptake by the Putrebactin-Mediated and Feo Systems in Shewanella oneidensis.

Shewanella oneidensis is an extensively studied bacterium capable of respiring minerals, including a variety of iron ores, as terminal electron acceptors (EAs). Although iron plays an essential and special role in iron respiration of S. oneidensis, little has been done to date to investigate the characteristics of iron transport in this bacterium. In this study, we found that all proteins encoded by the pub-putA-putB cluster for putrebactin (S. oneidensis native siderophore) synthesis (PubABC), recognition-transport of Fe3+-putrebactin across the outer membrane (PutA), and reduction of ferric putrebactin (PutB) are essential to putrebactin-mediated iron uptake. Although homologs of PutA are many, none can function as its replacement, but some are able to work with other bacterial siderophores. We then showed that Fe2+-specific Feo is the other primary iron uptake system, based on the synthetical lethal phenotype resulting from the loss of both iron uptake routes. The role of the Feo system in iron uptake appears to be more critical, as growth is significantly impaired by the absence of the system but not of putrebactin. Furthermore, we demonstrate that hydroxyl acids, especially α-types such as lactate, promote iron uptake in a Feo-dependent manner. Overall, our findings underscore the importance of the ferrous iron uptake system in metal-reducing bacteria, providing an insight into iron homeostasis by linking these two biological processes.IMPORTANCES. oneidensis is among the first- and the best-studied metal-reducing bacteria, with great potential in bioremediation and biotechnology. However, many questions regarding mechanisms closely associated with those applications, such as iron homeostasis, including iron uptake, export, and regulation, remain to be addressed. Here we show that Feo is a primary player in iron uptake in addition to the siderophore-dependent route. The investigation also resolved a few puzzles regarding the unexpected phenotypes of the putA mutant and lactate-dependent iron uptake. By elucidating the physiological roles of these two important iron uptake systems, this work revealed the breadth of the impacts of iron uptake systems on the biological processes.

Investigation of a spontaneous mutant reveals novel features of iron uptake in Shewanella oneidensis

Shewanella oneidensis is among the first and the best studied bacteria capable of respiring minerals as terminal electron acceptors (EAs), including a variety of iron ores. This respiration process relies on a large number of c-type cytochromes, which per se are iron-containing proteins. Thus, iron plays an essential and special role in iron respiration of S. oneidensis, prompting extensive investigations into iron physiology. Despite this, we still know surprisingly little about the components and characteristics of iron transport in this bacterium. Here, we report that TonB-dependent receptor PutA (SO_3033) is specific to the siderophore-mediated iron uptake. Although homologs of PutA are abundant, none of them can function as a replacement. In the absence of PutA, S. oneidensis suffers from an iron shortage, which leads to a severe defect in production of cytochrome c. However, proteins requiring other types of cytochromes, such as b and d, do not appear to be significantly impacted. Intriguingly, lactate, but not other carbon sources that are routinely used to support growth, is able to promote iron uptake when PutA is missing. We further show that the lactate-mediated iron import is independent of lactate permeases. Overall, our results suggest that in S. oneidensis the siderophore-dependent pathway plays a key role in iron uptake when iron is limited, but many alternative routes exist.

Intraspinal TLR4 activation promotes iron storage but does not protect neurons or oligodendrocytes from progressive iron-mediated damage

Iron is essential for basic cellular functions but in excess is highly toxic. For this reason, free iron and iron storage are controlled in the periphery by elaborate regulatory mechanisms. In contrast, iron regulation in the central nervous system (CNS) is not well defined. Given that excess iron is present after trauma, hemorrhagic stroke and neurodegeneration, understanding normal iron regulation and promoting iron uptake in CNS pathology is crucial. Peripherally, toll-like receptor 4 (TLR4) activation promotes iron sequestration by macrophages. Notably, iron-rich sites of CNS pathology typically contain TLR4 agonists, which may promote iron uptake. Indeed, our recent work showed impaired iron storage after acute spinal cord injury in mice with TLR4 deficiency. Here we used a reductionist model to ask if TLR4 activation in the CNS stimulates iron uptake and promotes neuroprotection from iron-induced toxicity. For this, we measured the ability of microglia/macrophages to sequester exogenous iron and prevent pathology with and without concomitant intraspinal TLR4 activation. Results show that, similar to the periphery, activating intraspinal TLR4 via focal LPS injection increased mRNA encoding iron uptake and storage proteins and promoted iron sequestration into ferritin-expressing macrophages. However, this did not prevent oligodendrocyte and neuron loss. Moreover, replacement of oligodendrocytes by progenitor cells – a normally robust response to in vivo macrophage TLR4 activation – was significantly reduced if iron was present concomitant with TLR4 activation. Thus, while TLR4 signaling promotes CNS iron uptake, future work needs to determine ways to enhance iron removal without blocking the reparative effects of innate immune receptor signaling.

Iron and Immunity.

Iron is an essential nutrient for most life on Earth because it functions as a crucial redox catalyst in many cellular processes. However, when present in excess iron can lead to the formation of harmful hydroxyl radicals. Hence, the cellular iron balance must be tightly controlled. Perturbation of iron homeostasis is a major strategy in host-pathogen interactions. Plants use iron-withholding strategies to reduce pathogen virulence or to locally increase iron levels to activate a toxic oxidative burst. Some plant pathogens counteract such defenses by secreting iron-scavenging siderophores that promote iron uptake and alleviate iron-regulated host immune responses. Mutualistic root microbiota can also influence plant disease via iron. They compete for iron with soil-borne pathogens or induce a systemic resistance that shares early signaling components with the root iron-uptake machinery. This review describes the progress in our understanding of the role of iron homeostasis in both pathogenic and beneficial plant-microbe interactions.

Sulfated glycosaminoglycan-derived oligosaccharides produced from chicken connective tissue promote iron uptake in a human intestinal Caco-2 cell line.

Food grade sulfated glycosaminoglycan (GAG) polysaccharides were successfully extracted from chicken cartilage and skin. Their respective oligosaccharides were obtained by bovine testicular hyaluronidase digestion. The antioxidant capacity was analyzed to determine the possible mechanism explaining how GAGs promote iron uptake by the Caco-2 cells. The sulfated GAG oligosaccharides derived from cartilage possessed the greatest DPPH scavenging and ferric reducing activities (p<0.05), but limited ferrous chelating activities. Both the cartilage and skin sulfated GAG polysaccharides showed greater ferritin formation compared to the negative control (p<0.05). Depolymerisation of GAG polysaccharides to oligosaccharides further improved ferritin formation by twofold. This research establishes that chicken sulfated GAG polysaccharides can enhance iron uptake by Caco-2 cells. The enhanced iron uptake through enzymatic GAG depolymerisation could be due to the combined effects of reduced molecular weight, increased amount of hydroxyl terminal groups and ferric reducing activities.

Improving the nutritional value of pulse crops

Improving the nutritional value of pulse crops

Tissue-Specific Regulation of Gibberellin Signaling Fine-Tunes Arabidopsis Iron-Deficiency Responses

Iron is an essential element for most living organisms. Plants acquire iron from the rhizosphere and have evolved different biochemical and developmental responses to adapt to a low-iron environment. In Arabidopsis, FIT encodes a basic helix-loop-helix transcription factor that activates the expression of iron-uptake genes in root epidermis upon iron deficiency. Here, we report that the gibberellin (GA)-signaling DELLA repressors contribute substantially in the adaptive responses to iron-deficient conditions. When iron availability decreases, DELLAs accumulate in the root meristem, thereby restraining root growth, while being progressively excluded from epidermal cells in the root differentiation zone. Such DELLA exclusion from the site of iron acquisition relieves FIT from DELLA-dependent inhibition and therefore promotes iron uptake. Consistent with this mechanism, expression of a non-GA-degradable DELLA mutant protein in root epidermis interferes with iron acquisition. Hence, spatial distribution of DELLAs in roots is essential to fine-tune the adaptive responses to iron availability.

Identification of Black Bean (Phaseolus vulgaris L.) Polyphenols That Inhibit and Promote Iron Uptake by Caco-2 Cells.

In nutritional studies, polyphenolic compounds are considered to be inhibitors of Fe bioavailability. Because they are presumed to act in a similar manner, total polyphenols are commonly measured via the Folin-Ciocalteu colorimetric assay. This study measured the content of polyphenolic compounds in white and black beans and examined the effect of individual polyphenols on iron uptake by Caco-2 cells. Analysis of seed coat extracts by LC-MS revealed the presence of a range of polyphenols in black bean, but no detectable polyphenols in white bean. Extracts from black bean seed coats strongly inhibited iron uptake. Examination of the eight most abundant black bean seed coat, non-anthocyanin polyphenols via Caco-2 cell assays showed that four (catechin, 3,4-dihydroxybenzoic acid, kaempferol, and kaempferol 3-glucoside) clearly promoted iron uptake and four (myricetin, myricetin 3-glucoside, quercetin, and quercetin 3-glucoside) inhibited iron uptake. The four inhibitors were present in 3-fold higher total concentration than the promoters (143 ± 7.2 vs 43.6 ± 4.4 μM), consistent with the net inhibitory effect observed for black bean seed coats. The ability of some polyphenols to promote iron uptake and the identification of specific polyphenols that inhibit Fe uptake suggest a potential for breeding bean lines with improved iron nutritional qualities.

A cascade of iron-containing proteins governs the genetic iron starvation response to promote iron uptake and inhibit iron storage in fission yeast.

Iron is an essential cofactor, but it is also toxic at high levels. In Schizosaccharomyces pombe, the sensor glutaredoxin Grx4 guides the activity of the repressors Php4 and Fep1 to mediate a complex transcriptional response to iron deprivation: activation of Php4 and inactivation of Fep1 leads to inhibition of iron usage/storage, and to promotion of iron import, respectively. However, the molecular events ruling the activity of this double-branched pathway remained elusive. We show here that Grx4 incorporates a glutathione-containing iron-sulfur cluster, alone or forming a heterodimer with the BolA-like protein Fra2. Our genetic study demonstrates that Grx4-Fra2, but not Fep1 nor Php4, participates not only in iron starvation signaling but also in iron-related aerobic metabolism. Iron-containing Grx4 binds and inactivates the Php4 repressor; upon iron deprivation, the cluster in Grx4 is probably disassembled, the proteins dissociate, and Php4 accumulates at the nucleus and represses iron consumption genes. Fep1 is also an iron-containing protein, and the tightly bound iron is required for transcriptional repression. Our data suggest that the cluster-containing Grx4-Fra2 heterodimer constitutively binds to Fep1, and upon iron deprivation the disassembly of the iron cluster between Grx4 and Fra2 promotes reverse metal transfer from Fep1 to Grx4-Fra2, and de-repression of iron-import genes. Our genetic and biochemical study demonstrates that the glutaredoxin Grx4 independently governs the Php4 and Fep1 repressors through metal transfer. Whereas iron loss from Grx4 seems to be sufficient to release Php4 and allow its nuclear accumulation, total or partial disassembly of the Grx4-Fra2 cluster actively participates in iron-containing Fep1 activation by sequestering its iron and decreasing its interaction with promoters.

Diphenyl-benzo[1,3]dioxole-4-carboxylic acid pentafluorophenyl ester: a convenient catechol precursor in the synthesis of siderophore vectors suitable for antibiotic Trojan horse strategies

Catechols are components of many metal-chelating compounds, including siderophores that are naturally occurring iron(III) chelators excreted by microorganisms. Catechol derivatives are poorly soluble in organic media and the synthesis of catechol-containing molecules requires the use of protected catechol precursors with improved organic solubility. We therefore developed 2,2-diphenyl-benzo[1,3]dioxole-4-carboxylic acid pentafluorophenyl ester. This activated ester reacts with an amine functionalized scaffold to generate chelators in which the catechol functions are protected in the form of diphenyl-benzodioxole moieties. The catechol can subsequently be deprotected, at the end of the synthesis, with trifluoroacetic acid (TFA). This strategy was applied to the synthesis of two catechol compounds functionalized with a terminal propargyl extension. These two compounds were shown to promote iron uptake in Escherichia coli and Pseudomonas aeruginosa. These two compounds are suitable for use as vectors in antibiotic Trojan horse approaches, as they could be conjugated with azide-functionalized antibiotics using the Huisgen dipolar 1,3-cycloaddition.

Secreted Pyomelanin of Legionella pneumophila Promotes Bacterial Iron Uptake and Growth under Iron-Limiting Conditions

Iron acquisition is critical to the growth and virulence of Legionella pneumophila. Previously, we found that L. pneumophila uses both a ferrisiderophore pathway and ferrous iron transport to obtain iron. We now report that two molecules secreted by L. pneumophila, homogentisic acid (HGA) and its polymerized variant (HGA-melanin, a pyomelanin), are able to directly mediate the reduction of various ferric iron salts. Furthermore, HGA, synthetic HGA-melanin, and HGA-melanin derived from bacterial supernatants enhanced the ability of L. pneumophila and other species of Legionella to take up radiolabeled iron. Enhanced iron uptake was not observed with a ferrous iron transport mutant. Thus, HGA and HGA-melanin mediate ferric iron reduction, with the resulting ferrous iron being available to the bacterium for uptake. Upon further testing of L. pneumophila culture supernatants, we found that significant amounts of ferric and ferrous iron were associated with secreted HGA-melanin. Importantly, a pyomelanin-containing fraction obtained from a wild-type culture supernatant was able to stimulate the growth of iron-starved legionellae. That the corresponding supernatant fraction obtained from a nonpigmented mutant culture did not stimulate growth demonstrated that HGA-melanin is able to both promote iron uptake and enhance growth under iron-limiting conditions. Indicative of a complementary role in iron acquisition, HGA-melanin levels were inversely related to the levels of siderophore activity. Compatible with a role in the ecology and pathogenesis of L. pneumophila, HGA and HGA-melanin were effective at reducing and releasing iron from both insoluble ferric hydroxide and the mammalian iron chelates ferritin and transferrin.

Overexpression of EVI1 Causes Genomic Instability and Cell Cycle Arrest in Hematopoietic Cells.

Abstract 2398Deregulated expression of the zinc finger transcription factor ecotropic viral integration site 1 (EVI1) is an independent poor prognostic marker for patients with acute myeloid leukemia. Moreover, we have recently shown that in clinical gene therapy of chronic granulomatous disease (cGD) the activation of this gene locus by strong promoter and enhancer elements within the gamma-retroviral vector LTR has led to clonal dominance and malignant transformation. Physiologically, EVI1 is essential for embryonic development and in regulating hematopoietic stem cell self-renewal. As very little is known about its molecular mechanism driving hematopoietic transformation towards leukemia, we aim to systematically analyze the role of deregulated EVI1 expression and its larger splice form MDS1/EVI1 in hematopoiesis.Lentiviral vector particles encoding for EVI1 (E) or MDS1/EVI1 (ME) and eGFP as marker protein were produced to stably overexpress the transgenes. Transgene expression was verified in myeloid HL60 cells by western blotting and immunofluorescence staining. Analysis of growth kinetics of human HL60 cells in suspension cultures revealed 1.5 – 3 folds lower cell counts of ME and E expressing cells as compared to eGFP control vector transduced cells. We further analyzed the expression of transferrin receptor CD71 which is mainly expressed on proliferating cells to promote iron uptake. Both, E and ME transduced cells, down-regulated CD71 during seven days in culture as compared to eGFP-transduced control cells. 64.2 ± 0.4% of ME cells and 31.1 ± 1.6% of E cells expressed CD71 compared to untransduced (97.4 ± 0.0%) and control vector cells (94.8 ± 0.8%) (p<0.001). For further analyzing the transgene effect on cell cycle activity, 3 populations with different intensity of transgene expression (negative, intermediate and high eGFP+ cells) were isolated. With raising ME expression a 5-fold decrease in the percentage of cells in sub-G1 phase but a 1.3-fold increase in the percentage of cells in G1/G0 phase of the cell cycle was detected. In the highly EVI1 expressing fraction 91.4% arrested in G1/G0 phase of the cell cycle (50.4% in G1/G0 phase in eGFP− E cells). Moreover, almost 1/3 of these transcription factor expressing cells (29.8 ± 8.3% of ME and 27.2 ± 1.6% of EVI1 positive cells) could be detected in G0 phase as compared to 5.0 ± 1.3% of control vector transduced cells. In human CD34+ hematopoietic cells, E and ME overexpression led to a decrease of eGFP+ cells from 8% at day 3 after transduction to 0.5 – 2.5% at day 14 in suspension culture. In contrast, the proportion of eGFP+ human primary cells remained stable for the time period analyzed after transduction with the control vector.We then asked if the cell cycle arrest in G0/G1 is associated with genetic instability, as patients with insertional activation of EVI1 developed a myelodysplastic syndrome with monosomy 7. Analyzing global gene expression comparing mock and eGFP control vector transduced cells with EVI1 expressing hematopoietic cells revealed more than 2000 differentially regulated genes. Genes involved in cell cycle regulation, recombination, replication and DNA repair were significantly downregulated upon EVI1 expression compared to control cells. For further studying DNA damage repair capacity, we irradiated EVI1- and eGFP-control vector transduced cells. Staining of γ-H2AX, an indirect marker for DNA double strand breaks (DSB), revealed that EVI1+ γ-H2AX+ cells were enriched almost 2-fold in G0/G1 phase of the cell cycle as compared to control vector transduced cells. The number of DSB positive cells decreased within 6 hours without apoptosis indicating that most of the double-strand breaks were repaired by non-homologous end-joining.In summary, our data show that EVI1 overexpression causes G0 cell cycle arrest of hematopoietic cells possibly associated with genetic instability. DSB repair in EVI1+ cells may subsequently lead to the accumulation of additional mutations. Systematic investigation of EVI1 and MDS1/EVI1 overexpression in human hematopoietic cells will gain insights into mechanisms leading to clonal dominance and malignant transformation. Disclosures:No relevant conflicts of interest to declare.

Insulin promotes iron uptake in human hepatic cell by regulating transferrin receptor-1 transcription mediated by hypoxia inducible factor-1

Hepatic iron is known to regulate insulin signaling pathways and to influence insulin sensitivity in insulin resistance (IR) patients. However, the role of insulin on hepatic iron homeostasis remains unexplored. Here, we report that insulin promotes transferrin-bound iron uptake but shows no influence on non transferrin-bound iron uptake in human hepatic HepG2 cells. As a mechanism we detected increased transferrin receptor-1 (TfR1) expression both at protein and mRNA levels. Unaltered stability of protein and transcript of TfR1 suggested the regulation at transcriptional level that was confirmed by promoter activity. Involvement of transcription factor hypoxia inducible factor-1 (HIF-1) was shown by mutational analyses of the TfR1 promoter region and by electrophoretic mobility shift assay. When HepG2 cells were transfected with specific siRNA targeted to 3′UTR of HIF-1α, the regulatory subunit of HIF-1; insulin-induced TfR1 expression and iron uptake were inhibited. Transfection of cDNA expressing stable form of HIF-1α reversed the increased TfR1 expression and iron uptake. These results suggest a novel role of insulin in hepatic iron uptake by a HIF-1 dependent transcriptional regulation of TfR1.

NGP1-01, a multi-targeted polycyclic cage amine, attenuates brain endothelial cell death in iron overload conditions

Development and progression of neurodegenerative disorders have, amongst other potential causes, been attributed to a disruption of iron regulatory mechanisms and iron accumulation. Excess extracellular iron may enter cells via nontraditional routes such as voltage-gated calcium channels and N-methyl-d-aspartate (NMDA) receptors leading to intracellular oxidative damage and ultimately mitochondrial failure. Nimodipine, an L-type calcium channel blocker has been shown to reduce iron-induced toxicity in neuronal and brain endothelial cells. Our current study investigates NGP1-01, a multimodal drug acting as an antagonist at both the NMDA receptor and the L-type calcium channel. Our previous studies support NGP1-01 as a promising neuroprotective agent in diseases involving calcium-related excitotoxicity. We demonstrate here that NGP1-01 (1 and 10μM) pretreatment abrogates the effects of iron overload in brain endothelial cells protecting cellular viability. Both concentrations of NGP1-01 were found to attenuate iron-induced reduction in cellular viability to a similar extent, and were statistically significant. To further verify the mechanism, the L-type calcium channel agonist FPL 64176 was administered to promote iron uptake. Addition of NGP1-01 dose-dependently reduced FPL 64176 stimulated uptake of iron. These data support further evaluation of NGP1-01 as a neuroprotective agent, not only in diseases associated with excitotoxicity, but also in those of iron overload.

Sll1263, a Unique Cation Diffusion Facilitator Protein that Promotes Iron Uptake in the Cyanobacterium Synechocystis sp. Strain PCC 6803

Cyanobacteria are known to survive in iron-deficient environments, but the ways in which they acquire Fe and acclimate are not completely understood. Here we report a novel gene sll1263 that is required for Synechocystis sp. strain PCC 6803 to grow under iron-deficient conditions. sll1263 encodes a putative cation diffusion facilitator protein (CDF) that shows 50% amino acid similarity with ferrous iron efflux protein (FieF) of heterotrophic bacteria. In bacteria, the gene product is involved in metal export from the cell, but in Synechocystis sll1263 plays a role in iron uptake. The results show that expression of sll1263 was induced by iron-deficient conditions and its inactivation significantly decreased the growth rate of an sll1263(-) mutant. Other genes known to be required for Fe acquisition were also strongly up-regulated in the mutant even in the presence of high Fe. Overexpression of sll1263 increased growth under iron deficiency but reduced growth under high-iron stress, suggesting that the gene product was involved in iron uptake rather than detoxification. Expression of FieF in the sll1263(-) mutant was unable to rescue the Fe-deficient phenotype, but Sll1263 completely restored it. Measurements of cellular iron content and the iron uptake rate showed that they were significantly less in the sll1263(-) mutant than in the wild type, consistent with a role for sll1263 in iron uptake. We hypothesize that the low-iron habitats and high-iron requirements of cyanobacteria may be the reason why cyanobacterial CDF protein functions in Fe uptake and not efflux as in non-photosynthetic bacteria.

Siderophores of Marinobacter aquaeolei: petrobactin and its sulfonated derivatives

Siderophores are low molecular weight, high-affinity iron(III) ligands, produced by bacteria to solubilize and promote iron uptake under low iron conditions. Two prominent structural features characterize the majority of the marine siderophores discovered so far: (1) a predominance of suites of amphiphilic siderophores composed of an iron(III)-binding headgroup that is appended by one or two of a series of fatty acids and (2) a prevalence of siderophores that contain alpha-hydroxycarboxylic acid moieties (e.g., beta-hydroxyaspartic acid or citric acid) which are photoreactive when coordinated to Fe(III). Variation of the fatty acid chain length affects the relative amphiphilicity within a suite of siderophores. Catecholate sulfonation is another structural variation that would affect the hydrophilicity of a siderophore. In addition to a review of the marine amphiphilic siderophores, we report the production of petrobactin disulfonate by Marinobacter aquaeolei VT8.

Isolated Glycosaminoglycans from Cooked Haddock Enhance Nonheme Iron Uptake by Caco-2 Cells

This study continues previous research to confirm that glycosaminoglycans (GAGs) exert a positive effect on promoting iron uptake by Caco-2 cells. Cooked haddock was digested with papain, and GAGs were further purified on the basis of their sulfur content. Reverse phase chromatography (RP-HPLC) and digestion with chondroitinase ABC (Chase) (50 mU/mg) were used to approach the identification of the GAGs. FeCl 3 was mixed with the purified GAGs, and Fe uptake was measured by ferritin formation using an in vitro digestion/Caco-2 cell model. The identificative analyses suggest that chondroitin/dermatan sulfate-related structures promote Fe uptake by Caco-2 cells; however, this effect was lower (40%) than that observed with whole fish muscle. Chase eliminated the positive effect on Fe uptake. These results indicate that specific GAGs may contribute to the enhancing effect of meat on Fe absorption. Further in vivo studies addressing these aspects of the meat factor are needed.

Vibrio choleraeVciB Promotes Iron Uptake via Ferrous Iron Transporters

Vibrio cholerae uses a variety of strategies for obtaining iron in its diverse environments. In this study we report the identification of a novel iron utilization protein in V. cholerae, VciB. The vciB gene and its linked gene, vciA, were isolated in a screen for V. cholerae genes that permitted growth of an Escherichia coli siderophore mutant in low-iron medium. The vciAB operon encodes a predicted TonB-dependent outer membrane receptor, VciA, and a putative inner membrane protein, VciB. VciB, but not VciA, was required for growth stimulation of E. coli and Shigella flexneri strains in low-iron medium. Consistent with these findings, TonB was not needed for VciB-mediated growth. No growth enhancement was seen when vciB was expressed in an E. coli or S. flexneri strain defective for the ferrous iron transporter Feo. Supplying the E. coli feo mutant with a plasmid encoding either E. coli or V. cholerae Feo, or the S. flexneri ferrous iron transport system Sit, restored VciB-mediated growth; however, no stimulation was seen when either of the ferric uptake systems V. cholerae Fbp and Haemophilus influenzae Hit was expressed. These data indicate that VciB functions by promoting iron uptake via a ferrous, but not ferric, iron transport system. VciB-dependent iron accumulation via Feo was demonstrated directly in iron transport assays using radiolabeled iron. A V. cholerae vciB mutant did not exhibit any growth defects in either in vitro or in vivo assays, possibly due to the presence of other systems with overlapping functions in this pathogen.