Iron deficiency: a concise review

Heme and non-heme iron transporters in non-polarized and polarized cells

Background

Heme and non-heme iron from diet, and recycled iron from hemoglobin are important products of the synthesis of iron-containing molecules. In excess, iron is potentially toxic because it can produce reactive oxygen species through the Fenton reaction. Humans can absorb, transport, store, and recycle iron without an excretory system to remove excess iron. Two candidate heme transporters and two iron transporters have been reported thus far. Heme incorporated into cells is degraded by heme oxygenases (HOs), and the iron product is reutilized by the body. To specify the processes of heme uptake and degradation, and the reutilization of iron, we determined the subcellular localizations of these transporters and HOs.

Results

In this study, we analyzed the subcellular localizations of 2 isoenzymes of HOs, 4 isoforms of divalent metal transporter 1 (DMT1), and 2 candidate heme transporters--heme carrier protein 1 (HCP1) and heme responsive gene-1 (HRG-1)--in non-polarized and polarized cells. In non-polarized cells, HCP1, HRG-1, and DMT1A-I are located in the plasma membrane. In polarized cells, they show distinct localizations: HCP1 and DMT1A-I are located in the apical membrane, whereas HRG-1 is located in the basolateral membrane and lysosome. 16Leu at DMT1A-I N-terminal cytosolic domain was found to be crucial for plasma membrane localization. HOs are located in smooth endoplasmic reticulum and colocalize with NADPH-cytochrome P450 reductase.

Conclusions

HCP1 and DMT1A-I are localized to the apical membrane, and HRG-1 to the basolateral membrane and lysosome. These findings suggest that HCP1 and DMT1A-I have functions in the uptake of dietary heme and non-heme iron. HRG-1 can transport endocytosed heme from the lysosome into the cytosol. These localization studies support a model in which cytosolic heme can be degraded by HOs, and the resulting iron is exported into tissue fluids via the iron transporter ferroportin 1, which is expressed in the basolateral membrane in enterocytes or in the plasma membrane in macrophages. The liberated iron is transported by transferrin and reutilized for hemoglobin synthesis in the erythroid system.

Anemia and its impact on function in nursing home residents: what do we know?

PURPOSE

To provide the advanced practice nurse (APN) information on the prevalence and causes of anemia in elderly nursing home (NH) residents, in order to affect diagnostic and management strategies that may help improve physical function and mobility outcomes.

DATA SOURCES

Literature review of current peer-reviewed research articles.

CONCLUSIONS

In the United States, the prevalence of anemia increases with advancing age, and are reported to be much higher among older NH residents than among community-dwelling older adults. Causes of anemia among the elderly are often multifactorial. Older individuals with anemia, including mild anemia and even low normal level, have demonstrated lower muscle strength, physical function, mobility, and increased morbidity and mortality outcomes.

IMPLICATIONS FOR PRACTICE

Given the potentially significant relationship between anemia and physical performance outcomes among NH residents, gaining a better understanding will help guide future evidence-based care by allowing the APN an opportunity to tailor both medical and restorative care interventions. Because anemia is a potentially modifiable condition, intervention may preserve, limit, or reverse functional impairment and/or disablement, and allow for maximal functional independence.

Evaluation and treatment of iron deficiency anemia: a gastroenterological perspective

A substantial volume of the consultations requested of gastroenterologists are directed towards the evaluation of anemia. Since iron deficiency anemia often arises from bleeding gastrointestinal lesions, many of which are malignant, establishment of a firm diagnosis usually obligates an endoscopic evaluation. Although the laboratory tests used to make the diagnosis have not changed in many decades, their interpretation has, and this is possibly due to the availability of extensive testing in key populations. We provide data supporting the use of the serum ferritin as the sole useful measure of iron stores, setting the lower limit at 100 microg/l for some populations in order to increase the sensitivity of the test. Trends of the commonly obtained red cell indices, mean corpuscular volume, and the red cell distribution width can provide valuable diagnostic information. Once the diagnosis is established, upper and lower gastrointestinal endoscopy is usually indicated. Nevertheless, in many cases a gastrointestinal source is not found after routine evaluation. Additional studies, including repeat upper and lower endoscopy and often investigation of the small intestine may thus be required. Although oral iron is inexpensive and usually effective, there are many gastrointestinal conditions that warrant treatment of iron deficiency with intravenous iron.

A possible link between iron deficiency and gastrointestinal carcinogenesis

There is definitive evidence that iron overload induces oxidative stress and DNA damage, which can enhance carcinogenic risk. However, other evidence suggests that iron deficiency and anemia also increase oxidative stress and DNA damage, which might increase carcinogenesis risk, especially in the gastrointestinal (GI) tract. The aim of this review is to provide essential background information for the accurate interpretation of future research on iron deficiency and increased GI cancer risk. Based on clinical, epidemiological, and experimental evidence, we discuss how iron deficiency might contribute to increased cancer risk through the impairment of several iron-dependent metabolic functions that are related to genome protection and maintenance (e.g., immune responses against cancer-initiated cells, metabolism of toxic compounds, and redox regulation of DNA biosynthesis and repair). Some epidemiological studies have indicated increased risk of GI tumors among individuals with low iron intake or low somatic iron stores, and in vivo data from rodent cancer models indicates the early progression of GI tumors during iron deficiency. Given the preliminary but consistent evidence relating iron deficiency to cancer risk and the fact that iron deficiency affects about one third of the world's population, further studies are needed to define the extent to which iron deficiency might increase GI cancer risk.

A chronic iron-deficient/high-manganese diet in rodents results in increased brain oxidative stress and behavioral deficits in the morris water maze

Iron deficiency (ID) is especially common in pregnant women and may even persist following childbirth. This is of concern in light of reports demonstrating that ID may be sufficient to produce homeostatic dysregulation of other metals, including manganese (Mn). These results are particularly important considering the potential introduction of the Mn-containing gas additive, methyl cyclopentadienyl manganese tricarbonyl (MMT), in various countries around the world. In order to model this potentially vulnerable population, we fed female rats fed either control (35 mg Fe/kg chow; 10 mg Mn/kg chow) or low iron/high-manganese (IDMn; 3.5 mg Fe/kg chow; 100 mg Mn/kg chow) diet, and examined whether these changes had any long-term behavioral effects on the animals' spatial abilities, as tested by the Morris water maze (MWM). We also analyzed behavioral performance on auditory sensorimotor gating utilizing prepulse inhibition (PPI), which may be related to overall cognitive performance. Furthermore, brain and blood metal levels were assessed, as well as regional brain isoprostane production. We found that treated animals were slightly ID, with statistically significant increases in both iron (Fe) and Mn in the hippocampus, but statistically significantly less Fe in the cerebellum. Additionally, isoprostane levels, markers of oxidative stress, were increased in the brain stem of IDMn animals. Although treated animals were indistinguishable from controls in the PPI experiments, they performed less well than controls in the MWM. Taken together, our data suggest that vulnerable ID populations exposed to high levels of Mn may indeed be at risk of potentially dangerous alterations in brain metal levels which could also lead to behavioral deficits.

Post-transcriptional regulation of gene expression in response to iron deficiency: co-ordinated metabolic reprogramming by yeast mRNA-binding proteins

Saccharomyces cerevisiae (baker's yeast) is an excellent model for understanding fundamental biological mechanisms that are conserved in Nature and that have an impact on human disease. The metal iron is a redox-active cofactor that plays critical biochemical roles in a broad range of functions, including oxygen transport, mitochondrial oxidative phosphorylation, chromatin remodelling, intermediary metabolism and signalling. Although iron deficiency is the most common nutritional disorder on the planet, little is known about the metabolic adjustments that cells undergo in response to iron deficit and the regulatory mechanisms that allow these adaptive responses. In the present article, we summarize recent work on genome-wide metabolic reprogramming in response to iron deficiency, mediated by specific mRNA degradation mechanisms that allow S. cerevisiae cells to adapt to iron deficiency.

Update of nutrient-deficiency anemia in elderly patients

Anemia, defined as a hemoglobin level < 13 g/dL in men and < 12 g/dL in women, is an important healthcare concern among the elderly. Nutrient-deficiency anemia represents one third of all anemias in elderly patients. About two thirds of nutrient-deficiency anemia is associated with iron deficiency and most of those cases are the result of chronic blood loss from gastrointestinal lesions. The remaining cases of nutrient-deficiency anemia are usually associated with vitamin B12, most frequently related to food-cobalamin malabsorption, and/or folate deficiency and are easily treated (nutrient-deficiency replacement).

Viral infection and iron metabolism

Fundamental cellular operations, including DNA synthesis and the generation of ATP, require iron. Viruses hijack cells in order to replicate, and efficient replication needs an iron-replete host. Some viruses selectively infect iron-acquiring cells by binding to transferrin receptor 1 during cell entry. Other viruses alter the expression of proteins involved in iron homeostasis, such as HFE and hepcidin. In HIV-1 and hepatitis C virus infections, iron overload is associated with poor prognosis and could be partly caused by the viruses themselves. Understanding how iron metabolism and viral infection interact might suggest new methods to control disease.

Intravenous iron: from anathema to standard of care

A growing body of literature supports the use of intravenous iron as a compliment to erythropoiesis stimulatory therapy and in a significant number of disease states where iron is necessary and oral iron is ineffective or not tolerated. The differences in efficacy, safety, and clinical nature of serious adverse events that occur with the various iron preparations are poorly understood. Misinterpretation of adverse events leads to underutilization of this important treatment modality. Understanding the history of the development and use of intravenous iron is crucial to appreciate its importance in the management of anemias of dialysis, cancer, and cancer chemotherapy and properly assess side effects and toxicity. The benefits seen with intravenous iron therapy are independent of the pretreatment levels of serum ferritin, iron, total iron binding capacity, and percent transferrin saturation. Intravenous iron has been shown to overcome hepcidin induced iron restricted erythropoiesis in iron-replete patients. Available clinical and experimental data suggest that increased utilization of intravenous iron should be considered.

Measuring brain manganese and iron accumulation in rats following 14 weeks of low-dose manganese treatment using atomic absorption spectroscopy and magnetic resonance imaging

Chronic exposure to manganese (Mn) may lead to a movement disorder due to preferential Mn accumulation in the globus pallidus and other basal ganglia nuclei. Iron (Fe) deficiency also results in increased brain Mn levels, as well as dysregulation of other trace metals. The relationship between Mn and Fe transport has been attributed to the fact that both metals can be transported via the same molecular mechanisms. It is not known, however, whether brain Mn distribution patterns due to increased Mn exposure vs. Fe deficiency are the same, or whether Fe supplementation would reverse or inhibit Mn deposition. To address these questions, we utilized four distinct experimental populations. Three separate groups of male Sprague-Dawley rats on different diets (control diet [MnT], Fe deficient [FeD], or Fe supplemented [FeS]) were given weekly intravenous Mn injections (3 mg Mn/kg body mass) for 14 weeks, whereas control (CN) rats were fed the control diet and received sterile saline injections. At the conclusion of the study, both blood and brain Mn and Fe levels were determined by atomic absorption spectroscopy and magnetic resonance imaging. The data indicate that changes in dietary Fe levels (either increased or decreased) result in regionally specific increases in brain Mn levels compared with CN or MnT animals. Furthermore, there was no difference in either Fe or Mn accumulation between FeS or FeD animals. These data suggest that dietary Fe manipulation, whether increased or decreased, may contribute to brain Mn deposition in populations vulnerable to increased Mn exposure.

Pathophysiology of anemia and erythrocytosis

An increasing understanding of the process of erythropoiesis raises some interesting questions about the pathophysiology, diagnosis and treatment of anemia and erythrocytosis. The mechanisms underlying the development of many of the erythrocytoses, previously characterised as idiopathic, have been elucidated leading to an increased understanding of oxygen homeostasis. Characterisation of anemia and erythrocytosis in relation to serum erythropoietin levels can be a useful addition to clinical diagnostic criteria and provide a rationale for treatment with erythropoiesis stimulating agents (ESAs). Recombinant human erythropoietin as well as other ESAs are now widely used to treat anemias associated with a range of conditions, including chronic kidney disease, chronic inflammatory disorders and cancer. There is also heightened awareness of the potential abuse of ESAs to boost athletic performance in competitive sport. The discovery of erythropoietin receptors outside of the erythropoietic compartment may herald future applications for ESAs in the management of neurological and cardiac diseases. The current controversy concerning optimal hemoglobin levels in chronic kidney disease patients treated with ESAs and the potential negative clinical outcomes of ESA treatment in cancer reinforces the need for cautious evaluation of the pleiotropic effects of ESAs in non-erythroid tissues.

Early influences and childhood development. Does helicobacter play a role?

In the late 1960s, Rene Dubos showed that a variety of nutritional stress in utero or in early infancy could have dramatic impact on childhood development that was irreversible. This included detectable changes in the brain. Since that time, iron deficiency anemia (IDA) has been identified as one of the major nutritional stresses that leads to permanent behavioral changes in both experimental animals and humans resulting in poorer cognitive, motor, and social-emotional function. It has been proposed that these changes play an important part in the inter-generational transmission of poverty. More recently, it is becoming clear that Helicobacter pylori causes IDA in populations on an iron-limiting diet. The main thesis of this article is that H. pylori infection may indeed have an impact on childhood development and that much more research is needed in this area as intervention via immunization or antimicrobial therapy in populations in the developing world may have major positive benefits via cure of IDA and prevention of brain damage in the young.

Nutritional iron deficiency

Iron deficiency is one of the leading risk factors for disability and death worldwide, affecting an estimated 2 billion people. Nutritional iron deficiency arises when physiological requirements cannot be met by iron absorption from diet. Dietary iron bioavailability is low in populations consuming monotonous plant-based diets. The high prevalence of iron deficiency in the developing world has substantial health and economic costs, including poor pregnancy outcome, impaired school performance, and decreased productivity. Recent studies have reported how the body regulates iron absorption and metabolism in response to changing iron status by upregulation or downregulation of key intestinal and hepatic proteins. Targeted iron supplementation, iron fortification of foods, or both, can control iron deficiency in populations. Although technical challenges limit the amount of bioavailable iron compounds that can be used in food fortification, studies show that iron fortification can be an effective strategy against nutritional iron deficiency. Specific laboratory measures of iron status should be used to assess the need for fortification and to monitor these interventions. Selective plant breeding and genetic engineering are promising new approaches to improve dietary iron nutritional quality.

Total iron binding capacity or transferrin concentration alone outperforms iron and saturation indices in predicting iron deficiency

BACKGROUND

Although serum ferritin measurement is the investigation of choice in iron deficiency, many laboratories continue to offer iron and TIBC/transferrin measurements. With increasing use of direct transferrin measurement, the possibility of reporting transferrin concentration alone without iron or transferrin saturation arises. This study compared the diagnostic utility of iron, transferrin and transferrin saturation measurements in the diagnosis of iron deficiency

METHODS

Details of all laboratory requests for simultaneous serum iron, transferrin/TIBC and ferritin measurement were analysed to assess the diagnostic performance of iron, transferrin or TIBC, and transferrin saturation or TIBC saturation in identifying unequivocal iron deficiency (using 2 different serum ferritin cutoffs: <12 and <15 microg/l). The dataset was divided into 3 groups based on various reagent combinations.

RESULTS

Across inpatient and outpatient populations and all 3 reagent combinations, transferrin or TIBC measurement outperformed iron measurement and saturation index. Mean areas under ROC curves across the study were: transferrin or TIBC: 0.94; Fe 0.77; saturation 0.87. There was no difference in diagnostic performance between transferrin and the 2 TIBC formulations.

CONCLUSIONS

Transferrin or TIBC measurement outperforms iron and saturation in predicting iron deficiency. This approach offers a cost-effective, evidence-based approach to the investigation of iron deficiency.

Enhanced Expression of High-affinity Iron Transporters via H-ferritin Production in Yeast

Our heterologous expression system of the human ferritin H-chain gene (hfH) allowed us to characterize the cellular effects of ferritin in yeasts. The recombinant Saccharomyces cerevisiae (YGH2) evidenced impaired growth as compared to the control, which was correlated with ferritin expression and with the formation of core minerals. Growth was recovered via the administration of iron supplements. The modification of cellular iron metabolism, which involved the increased expression of high-affinity iron transport genes (FET3 and FTR1), was detected via Northern blot analysis. The findings may provide some evidence of cytosolic iron deficiency, as the genes were expressed transcriptionally under iron-deficient conditions. According to our results examining reactive oxygen species (ROS) generation via the fluorescence method, the ROS levels in YGH2 were decreased compared to the control. It suggests that the expression of active H-ferritins reduced the content of free iron in yeast. Therefore, present results may provide new insights into the regulatory network and pathways inherent to iron depletion conditions.

Metabolic regulation of citrate and iron by aconitases: role of iron–sulfur cluster biogenesis

Iron and citrate are essential for the metabolism of most organisms, and regulation of iron and citrate biology at both the cellular and systemic levels is critical for normal physiology and survival. Mitochondrial and cytosolic aconitases catalyze the interconversion of citrate and isocitrate, and aconitase activities are affected by iron levels, oxidative stress and by the status of the Fe-S cluster biogenesis apparatus. Assembly and disassembly of Fe-S clusters is a key process not only in regulating the enzymatic activity of mitochondrial aconitase in the citric acid cycle, but also in controlling the iron sensing and RNA binding activities of cytosolic aconitase (also known as iron regulatory protein IRP1). This review discusses the central role of aconitases in intermediary metabolism and explores how iron homeostasis and Fe-S cluster biogenesis regulate the Fe-S cluster switch and modulate intracellular citrate flux.

Diabetes, metallothionein, and zinc interactions: a review

Epidemiological evidence, associating diabetes with zinc (Zn) deficiencies, has resulted in numerous research studies describing the effects of Zn and associated metallothionein (MT), on reducing diabetic complications associated with oxidative stress. MT has been found to have a profound effect on the reduction of oxidative stress induced by the diabetic condition. Over expression of MT in various metabolic organs has also been shown to reduce hyperglycaemia-induced oxidative stress, organ specific diabetic complications, and DNA damage in diabetic experimental animals, which have been further substantiated by the results from MT-knockout mice. Additionally, supplementation with Zn has been shown to induce in vivo MT synthesis in experimental animals and to reduce diabetes related complications in both humans and animal models. Although the results are promising, some caution regarding this topic is however necessary, due to the fact that the majority of the studies done have been animal based. Hence more human intervention trials are needed regarding the positive effects of MT and Zn before firm conclusions can be made regarding their use in the treatment of diabetes.

Molecular and clinical aspects of iron homeostasis: From anemia to hemochromatosis

The discovery in recent years of a plethora of new genes whose products are implicated in iron homeostasis has led to rapid expansion of our knowledge in the field of iron metabolism and its underlying complex regulation in both health and disease. Abnormalities of iron metabolism are among the most common disorders encountered in practical medicine and may have significant negative impact on physical condition and life expectancy. Basic insights into the principles of iron homeostasis and the pathophysiological and clinical consequences of iron overload, iron deficiency and misdistribution are thus of crucial importance in modern medicine. This review summarizes our current understanding of human iron metabolism and focuses on the clinically relevant features of hereditary and secondary hemochromatosis, iron deficiency anemia, anemia of chronic disease and anemia of critical illness. The interconnections between iron metabolism and immunity are also addressed, in as much as they may affect the risk and course of infections and malignancies.

Oral administration of lactoferrin increases hemoglobin and total serum iron in pregnant womenThis paper is one of a selection of papers published in this Special Issue, entitled 7th International Conference on Lactoferrin: Structure, Function, and Applications, and has undergone the Journal's usual peer review process

Iron deficiency anemia (IDA) during pregnancy continues to be of world-wide concern. IDA is a risk factor for preterm delivery and subsequent low birth weight, and possibly for poor neonatal health. Iron supplementation in pregnancy is a widely recommended practice, yet intervention programs have met with many controversies. In our study, 300 women at different trimesters of pregnancy were enrolled in a trial of oral administration of ferrous sulfate (520 mg once a day) or 30% iron-saturated bovine lactoferrin (bLf) (100 mg twice a day). Pregnant women refusing treatment represented the control group. In this group hemoglobin and total serum iron values measured after 30 d without treatment decreased significantly, especially in women at 18–31 weeks of pregnancy. In contrast, after 30 d of oral administration of bLf, hemoglobin and total serum iron values increased and to a greater extent than those observed in women treated orally for 30 d with ferrous sulfate, independently of the trimester of pregnancy. Unlike ferrous sulfate, bLf did not result in any side effects. These findings lead us to hypothesize that lactoferrin could influence iron homeostasis directly or through other proteins involved in iron transport out of the intestinal cells into the blood.

The diagnosis and treatment of iron deficiency and its potential relationship to hair loss

Iron deficiency is the world's most common nutritional deficiency and is associated with developmental delay, impaired behavior, diminished intellectual performance, and decreased resistance to infection. In premenopausal women, the most common causes of iron deficiency anemia are menstrual blood loss and pregnancy. In men and postmenopausal women, the most common causes of iron deficiency anemia are gastrointestinal blood loss and malabsorption. Hemoglobin concentration can be used to screen for iron deficiency, whereas serum ferritin concentration can be used to confirm iron deficiency. However, the serum ferritin concentration may be elevated in patients with infectious, inflammatory, and neoplastic conditions. Other tests may be needed, such as erythrocyte zinc protoporphyrin concentration, transferrin concentration, serum iron concentration, and transferrin saturation. The cause of iron deficiency must be identified. If the patient is male, postmenopausal female, or has risk factors for blood loss, then the patient should be evaluated for sources of blood loss, especially gastrointestinal (eg, colon cancer). Several studies have examined the relationship between iron deficiency and hair loss. Almost all have addressed women exclusively and have focused on noncicatricial hair loss. Some suggest that iron deficiency may be related to alopecia areata, androgenetic alopecia, telogen effluvium, and diffuse hair loss, while others do not. Currently, there is insufficient evidence to recommend universal screening for iron deficiency in patients with hair loss. In addition, there is insufficient evidence to recommend giving iron supplementation therapy to patients with hair loss and iron deficiency in the absence of iron deficiency anemia. The decision to do either should be based on clinical judgment. It is our practice at the Cleveland Clinic Foundation to screen male and female patients with both cicatricial and noncicatricial hair loss for iron deficiency. Although this practice is not evidence based per se, we believe that treatment for hair loss is enhanced when iron deficiency, with or without anemia, is treated. Iron deficiency anemia should be treated. Treating iron deficiency without anemia is controversial. Treatment of nutritional iron deficiency anemia includes adequate dietary intake and oral iron supplementation. Excessive iron supplementation can cause iron overload and should be avoided, especially in high-risk patients such as those with hereditary hemochromatosis. Patients who do not respond to iron replacement therapy should undergo additional testing to identify other underlying causes of iron deficiency anemia.

Assessment of cardiac function in iron-deficient children without anemia

Iron deficiency anemia may lead to impairment of many vital functions, including those in the cardiovascular system. However, the effects of iron depletion on cardiac function in the absence of anemia are not well known. In this study the authors examined the effects of iron deficiency without overt anemia on cardiac function in 59 children. Complete blood count, serum iron, serum iron-binding capacity, and serum ferritin levels were measured in all children. The children were divided into two groups according to serum ferritin levels: an iron-depleted group (n = 28) and a non-iron-depleted control group (n = 31). Echocardiographic examinations were performed using M mode and Doppler echocardiographic methods in all children to assess cardiac function. No statistically significant difference was found between the two groups in terms of echocardiographic indices. Although the number of subjects in this study was small, the authors conclude that iron deficiency in the absence of overt anemia does not lead to important changes in cardiac function.

Incorporating a rapid-impact package for neglected tropical diseases with programs for HIV/AIDS, tuberculosis, and malaria

Hotez et al. argue that achieving success in the global fight against HIV/AIDS, tuberculosis, and malaria may well require a concurrent attack on the neglected tropical diseases.

Iron salts perturb biofilm formation and disrupt existing biofilms of Pseudomonas aeruginosa

Bacterial biofilms are thought to aid in the survivability of a variety of intractable infections in humans. Specifically, biofilm production in Pseudomonas aeruginosa has been shown to play a significant role in chronic infection of cystic fibrosis (CF) patients. Unfortunately, no clinically effective inhibitors of biofilm formation are available. A rapid screen of 4509 compounds for nonantibiotic biofilm inhibitors in Pseudomonas aeruginosa PA14 was executed in 384-well plates. Among those compounds, ferric ammonium citrate inhibited biofilm formation in a dose-dependent manner; other iron salts functioned similarly. In addition to biofilm inhibition in static culture, pregrown biofilms could be disrupted and cleared by switching to iron-rich media in flow-chamber experiments. Furthermore, P. aeruginosa strains taken from the sputum of 20 CF patients showed a similar response to elevated iron levels. Previous expression-profiling analyses demonstrated that high levels of iron repress the expression of genes whose products are essential for scavenging iron and that expression of these genes is critical for virulence. Our results, combined with existing transcriptional-profiling data, now indicate that elevated iron concentrations repress the expression of certain genes essential for biofilm production in P. aeruginosa.