Absence Of Iron Research Articles

Oxygen controls on magmatism in rocky exoplanets

Refractory oxygen bound to cations is a key component of the interior of rocky exoplanets. Its abundance controls planetary properties including metallic core fraction, core composition, and mantle and crust mineralogy. Interior oxygen abundance, quantified with the oxygen fugacity (fO2), also determines the speciation of volatile species during planetary outgassing, affecting the composition of the atmosphere. Although melting drives planetary differentiation into core, mantle, crust, and atmosphere, the effect of fO2 on rock melting has not been studied directly to date, with prior efforts focusing on fO2-induced changes in the valence ratio of transition metals (particularly iron) in minerals and magma. Here, melting experiments were performed using a synthetic iron-free basalt at oxygen levels representing reducing (log fO2 = -11.5 and -7) and oxidizing (log fO2 = -0.7) interior conditions observed in our solar system. Results show that the liquidus of iron-free basalt at a pressure of 1 atm is lowered by 105 ± 10 °C over an 11 log fO2 units increase in oxygen abundance. This effect is comparable in size to the well-known enhanced melting of rocks by the addition of H2O or CO2 This implies that refractory oxygen abundance can directly control exoplanetary differentiation dynamics by affecting the conditions under which magmatism occurs, even in the absence of iron or volatiles. Exoplanets with a high refractory oxygen abundance exhibit more extensive and longer duration magmatic activity, leading to more efficient and more massive volcanic outgassing of more oxidized gas species than comparable exoplanets with a lower rock fO2.

Generation of singlet oxygen via iron-dependent lipid peroxidation and its role in Ferroptosis

Ferroptosis is a cell death pathway mediated by iron-dependent accumulation of lipid peroxide. However, the specific downstream molecular events of iron-dependent lipid peroxidation are yet to be elucidated. In this study, based on various spectral analyses, we have found evidence that singlet oxygen is produced through the Russell mechanism during the self-reaction of lipid peroxyl radicals generated via iron-dependent lipid peroxidation regardless of the presence of cholesterol. Significantly reduced generation of singlet oxygen was observed in the absence of iron. The generated singlet oxygen accelerated the oxidative damage of lipid membranes by propagating lipid peroxidation and facilitated ferroptotic cancer cell death initiated by erastin. In this work, singlet oxygen has been revealed to be a new reactive species that participates in ferroptosis, thus improving the understanding on iron-dependent lipid peroxidation and the mechanism of ferroptosis.

CosR Regulation of perR Transcription for the Control of Oxidative Stress Defense in Campylobacter jejuni.

Oxidative stress resistance is an important mechanism to sustain the viability of oxygen-sensitive microaerophilic Campylobacter jejuni. In C. jejuni, gene expression associated with oxidative stress defense is modulated by PerR (peroxide response regulator) and CosR (Campylobacter oxidative stress regulator). Iron also plays an important role in the regulation of oxidative stress, as high iron concentrations reduce the transcription of perR. However, little is known about how iron affects the transcription of cosR. The level of cosR transcription was increased when the defined media MEMα (Minimum Essential Medium) was supplemented with ferrous (Fe2+) and ferric (Fe3+) iron and the Mueller–Hinton (MH) media was treated with an iron chelator, indicating that iron upregulates cosR transcription. However, other divalent cationic ions, such as Zn2+, Cu2+, Co2+, and Mn2+, did not affect cosR transcription, suggesting that cosR transcription is regulated specifically by iron. Interestingly, the level of perR transcription was increased when CosR was overexpressed. The positive regulation of perR transcription by CosR was observed both in the presence or in the absence of iron. The results of the electrophoretic mobility shift assay showed that CosR directly binds to the perR promoter. DNase I footprinting assays revealed that the CosR binding site in the perR promoter overlaps with the PerR box. In the study, we demonstrated that cosR transcription is increased in iron-rich conditions, and CosR positively regulates the transcription of PerR, another important regulator of oxidative stress defense in C. jejuni. These results provide new insight into how C. jejuni regulates oxidative stress defense by coordinating the transcription of perR and cosR in response to iron.

Influence of Iron on Physiological Parameters and Intracellular Microcystin in Microcystis Panniformis Strain Isolated from a Reservoir in the Amazon.

In the Amazon, the leaching from soil left unprotected by deforestation increases the entry of iron, among other elements, in aquatic ecosystems, which can cause cyanobacterial blooms. This study aimed to investigate the physiological response of a strain of Microcystis panniformis to iron variation. The strain was isolated from a reservoir located in the Western Amazon and produces microcystin-LR. After a period of iron deprivation, the cultures were submitted to three conditions: control (223 μgFe.L-1), treatment with 23 μgFe.L-1, and absence of iron. At regular intervals for eight days, the cell density, levels of chlorophyll a and microcystins were determined. On the second and fourth day, transcription of genes responsive to iron limitation was quantified. Starting on the fourth day of the experiment, the different iron concentrations affected growth, and on the eighth day in the iron-free condition cell density was 90% lower than in control. Chlorophyll cell quota in 23 μgFe.L-1 and control presented similar values, while without iron the cells became chlorotic as of the fourth day Toxin concentration in cells grow in 0 μgFe.L-1 in relation to the control. Higher transcription levels of the feo and fut genes were observed in the 0 μgFe.L-1 and 23 μgFe.L-1 treatments, indicating that the cells were activating high-affinity capture systems to reestablish an adequate concentration of intracellular iron. The increasing deforestation in the Jamari River Basin (Amazon region), can contribute to the occurrence of toxic cyanobacterial blooms due to the greater entrance of iron in water bodies.

Ciprofloxacin-Resistant Staphylococcus aureus Displays Enhanced Resistance and Virulence in Iron-Restricted Conditions.

The unreasonable misuse of antibiotics has led to the emergence of large-scale drug-resistant bacteria, seriously threatening human health. Compared with drug-sensitive bacteria, resistant bacteria are difficult to clear by host immunity. To fully explore the adaptive mechanism of resistant bacteria to the iron-restricted environment, we performed data-independent acquisition-based quantitative proteomics on ciprofloxacin (CIP)-resistant (CIP-R) Staphylococcus aureus in the presence or absence of iron. On bioinformatics analysis, CIP-R bacteria showed stronger amino acid synthesis and energy storage ability. Notably, CIP-R bacteria increased virulence by upregulating the expression of many virulence-related proteins and enhancing the synthesis of virulence-related amino acids under iron-restricted stress. This study will help us to further explain the adaptive mechanisms that lead to bacterial resistance to antibiotics depending on the host environment and provide insights into the development of novel drugs for the treatment of drug-resistant bacterial infections.

Iron Binding in an Ethylenediaminetetracetic Acid‐Based Gemini Surfactant Monolayer Film

AbstractThe ability of Fe3+ to bind to Langmuir monolayers of an N, N, N′, N′‐dialkyl‐N, N′‐diacetate ethylenediamine gemini surfactant has been explored. Fe3+ in the subphase resulted in the formation of compacted, liquid‐phase monolayers with a mesh‐like morphology at the micron length scale in comparison with expanded, unstructured liquid‐phase monolayers in the absence of iron. The response of the monolayer to subphase Fe3+ was different from that reported for Na+ and Ca2+ for an affiliated, shorter‐tail gemini surfactant. Combined surface potential and X‐ray reflectivity measurements indicated that Fe3+ induced minor conformational changes in the monolayer, suggesting ionic association with the head group. Direct evidence for the binding of iron was provided by total reflection X‐ray fluorescence measurements, which revealed that multiple ions were associated with each head group as opposed to chelating with 1:1 stoichiometry as observed with bulk ethylenediaminetetracetic acid. Cumulative data suggest the adsorption of Fex(OH)y(3x−y)+ complexes with the monolayer surface as has been reported with other charged and uncharged monolayers.

Multimodal imaging of muon based on scattering and secondary induced neutrons

Muon scattering imaging technology can be used to detect nuclear material and is of considerable significance in nuclear safety. However, it is difficult to distinguish special nuclear materials from high-Z objects effectively by using the existing muon scattering imaging technologies. Muon-induced neutrons emitted from special nuclear materials can help to identify the existence of special nuclear materials. However, this method has long imaging time and low imaging quality. Multimodal imaging of muon uses both the information about scattering muons penetrating the material and the information about muons stopped by material and generating secondary induced neutrons, which can overcome the shortcomings of single imaging method effectively. The detection model is set up based on Geant4. The simulation programs of muon imaging in coincidence with muon induced neutrons, scattering imaging of muon, and multimodal imaging of muon are developed by using Cosmic-ray Shower Library as particle source, and the imaging algorithms are implemented respectively on the basis of the simulated data. Two imaging models are designed for muon scattering imaging. The first one is a single <sup>235</sup>U cube, and the second one is composed of four cubes, namely <sup>235</sup>U cube, <sup>239</sup>Pu cube, lead cube and aluminum cube. This simulation has completed muon scattering imaging of single cube and four cubes. In the part of muon imaging in coincidence with muon induced neutrons, the neutronic gain of the HEU (90% <sup>235</sup>U) plate, LEU (20% <sup>235</sup>U) plate, and DU (0.2% <sup>235</sup>U) plate, as well as the relationship between the neutronic gain of these three uranium plates and the energy and charged properties of the muon are obtained by simulation, and then two imaging models are set up. The first one is composed of four cubes, namely <sup>235</sup>U cube, <sup>239</sup>Pu cube, lead cube, and aluminum cube, and the other is comprised of multilayer nuclear components. The 2D and 3D reconstruction results of multi-objects and multilayer nuclear components are obtained through muon imaging in coincidence with muon induced neutrons. Then the multimodal imaging of muon for three cubes is realized in the presence or absence of iron shielding shell. The imaging capabilities are compared with the muon scattering imaging capacities and muon imaging capacities in coincidence with muon induced neutrons. Simulation studies indicate that multimodal imaging of muon based on scattering and secondary induced neutrons can effectively combine the advantages of every single imaging method. The multimodal imaging of muon can take advantage of available information more efficiently, which is helpful in improving the imaging quality. Multimodal imaging of muon not only has the advantages of short imaging time and high imaging quality, but also can distinguish special nuclear material from other high-Z materials clearly, which is vital for detecting special nuclear materials.

Influence of irradiation sources on the efficiency of copper-modified magnetite for photo-Fenton degradation of sulfathiazole

A comparison of the catalytic activity of the copper-modified magnetite was carried out under different conditions (dark and irradiated) and irradiation systems (460 nm Vis-LED, 370 nm UV-LED and Solar) in the degradation of the antibiotic sulfathiazole (STZ). The catalyst copper-modified magnetite presented a mesoporous structure, with a high absorption range (200–800 nm), band gap of 1.80 eV characteristic of iron and copper oxides, negative surface charge (− 24.6 mV) at neutral pH and high stability in solution (absence of iron and copper leaching). The results showed that the degradation kinetics of STZ increased in the following order in relation to irradiation: dark < Vis-LED < UV-LED < Solar), promoting complete degradation after 15 min, indicating that under solar and UV irradiation the catalytic activity is improved, due to an increase in the speed of the Fe–Cu redox reactions from a quick transfer of electrons that occur on the surface of the catalyst, further facilitating the formation of HO· radicals. The results have further demonstrated that the copper-modified magnetite can promote heterogeneous Fenton processes under LED or solar irradiation and be applied to effective degradation of micropollutants in wastewaters and have proven the versatility and high catalytic activity.

Treatment of manganese, in the presence or absence of iron, in acid and neutral mine drainage using raw vs half-calcined dolomite

Efficient removal of Mn from mine drainage is complex because of its high solubility minerals, especially in the presence of Fe. This study evaluates the comparative efficiency of raw and half-calcined dolomite for Mn removal in synthetic and real contaminated neutral drainage (CND) as well as in real acid mine drainage (AMD). Batch isotherms were used to evaluate the removal of Mn by raw and half-calcined dolomite, in the presence or the absence of Fe, in synthetic CND and in synthetic AMD. Batch kinetics tests were also performed, only for synthetic CND, in the absence of Fe. Raw dolomite showed limited efficiency in batch tests. Hence, only the half-calcined dolomite was used in column tests. Removal of Mn from synthetic CND (pH 6.84; 46.1 mg/L Mn) was effective for 106 days. For the following 119 days of monitoring, Mn was treated ≥95%. For Mn removal in real AMD (pH 2.40; 22.8 mg/L Mn and 679 mg/L Fe), half-calcined dolomite proved less effective. After 1 week, Mn, Ni and Zn were no longer treated, whereas after 3 weeks, the pH and the concentration of Cu in the final effluent were also no longer conform to the Canadian discharge criteria. In the same time, Co, Cr and Fe were still removed even after 8 weeks. For the real CND, Mn concentration decreased by >90% (0.65 mg/L at the inlet and 0.05 mg/L at the exit) with half-calcined dolomite. Therefore, half-calcined dolomite seems highly promising for the treatment of Mn in CND.

Effectiveness of the Iron Chelator CN128 in Mitigating the Formation of Dopamine Oxidation Products Associated with the Progression of Parkinson's Disease.

The occurrence and progression of Parkinson's disease (PD) has been associated with the observation of elevated iron concentrations in the substantia nigra pars compacta (SNpc). While the reasons for the impact of elevated iron concentrations remain unclear, one hypothesis is that the presence of labile iron induces the oxidation of dopamine (DA) to toxic quinones such as aminochrome (DAC) and reactive oxygen species (ROS). As such, one of the proposed therapeutic strategies has been the use of iron chelators such as deferiprone (DFP) (which is recognized to have limitations related to its rapid degradation in the liver) to reduce the concentration of labile iron. In this study, a detailed investigation regarding the novel iron chelator, CN128, was conducted and a kinetic model developed to elucidate the fundamental behavior of this chelator. The results in this work reveal that CN128 is effective in alleviating the toxicity induced by iron and DA to neurons when DA is present at moderate concentrations. When all the iron is chelated by CN128, the formation of DAC and the oxidation of DA can be reduced to levels identical to that in the absence of iron. The production of H2O2 is lower than that generated via the autoxidation of the same amount of DA. However, when severe leakage of DA occurs, the application of CN128 is insufficient to alleviate the associated toxicity. This is attibuted to the less important role of iron in the production of toxic intermediates at high concentrations of DA. CN128 is superior to DFP with regard to the reduction in formation of DAC and elevation in DA concentration. In summary, the results of this study suggest that prodromal application of the chelator CN128 could be effective in preventing the onset and slowing the early stage development of PD symptoms associated with oxidants and toxic intermediates resulting from the iron-mediated oxidation of the neurotransmitter dopamine with CN128 likely to be superior to DFP in view of its greater in vivo availability and less problematic side effects.

Kinetic models of zinc dissolution from artificial sphalerite with different iron contents in oxygen pressure leaching

ABSTRACT The oxygen pressure leaching of sphalerite in sulphuric acid solutions is a slow process in the absence of iron because of the limitations of the oxygen delivery carrier (redox couple: Fe3+/Fe2+). Herein, the artificial sphalerite with 25.70%, 15.20%, 5.75% iron contents and non-iron was prepared via the sintering of ZnS and FeS and used in the kinetic oxygen pressure leaching experiment. The results indicated that the zinc leaching rate of non-iron sphalerite was significantly lower than those of sphalerite with 25.70%, 15.20%, and 5.75% iron contents. This ratio decreased from 90 to 98% to approximately 65% at a temperature of 403 K, sulphuric acid concentration of 110 g L−1, oxygen partial pressure of 0.8 MPa, and leaching time of 70 min. Furthermore, when compared to the artificial sphalerite with 25.70%, 15.20%, 5.75% iron contents, the activation energy decreased from 32.31 kJ mol−1 for non-iron sphalerite to 29.02, 26.30, and 21.60 kJ mol−1, respectively. The leaching reaction process followed a shrinking unreacted core model that gradually shifted from surface reaction control to diffusion control. The orders of reaction for the sulphuric acid concentration and oxygen partial pressure were also obtained. Finally, artificial sphalerite leaching kinetics model equations with different iron contents were established.

Understanding the role of iron (III) tosylate on heavy oil viscosity reduction

Heavy oil is an abundant energy resource, but its recovery remains challenging primarily due to its high viscosity. Thermally enhanced oil recovery in the presence of metal-ligand compounds (MLCs) has been studied as a promising method for in situ viscosity reduction and oil quality upgrading. In spite of its importance, the interactions between MLCs and crude oil components at the molecular-level are poorly understood, and their mechanistic details for viscosity reduction are unclear. Here we studied viscosity changes of Peace River oil in the range of 80–295 °C in the presence and absence of iron (III) tosylate (para-toluenesulfonate) MLC and analyzed reaction products via viscometry, TGA-MS, XPS, GC-MS, SARA analysis, and elemental analysis. Whereas thermal treatment lowered viscosity at 190 °C and above, thermal treatment with the iron tosylate MLC decreased viscosity only at temperatures above 230 °C. The MLC effect was most substantial at 280 °C, at which viscosity decreased by 58% (compared to 39% in absence of the MLC at the same temperature). The MLC likely lowered oil viscosity by catalytically reacting with the asphaltene to decrease its total content in oil, and by releasing a ligand to form 4-methylbenzenethiol (MBT) that interfered with asphaltene intermolecular interactions. At temperatures below 230 °C, the MLC unexpectedly raised oil viscosity, likely due to bridging interactions with asphaltene. This understanding of MLC-induced deviscosification provides a selection rationale for appropriate metals and ligands for enhancing heavy oil recovery.

Effects of Trichoderma asperellum and its siderophores on endogenous auxin in Arabidopsis thaliana under iron-deficiency stress.

Iron (Fe) deficiency is one of the major limiting factors affecting crop yields. Trichoderma asperellum Q1, a biocontrol and plant growth promoting fungus, can produce the siderophore which has a high affinity to Fe3+ in the absence of iron. In this study, Trichoderma asperellum Q1 was found to be able to promote growth of Arabidopsis thaliana in an iron-deficient or insoluble iron-containing (Fe2O3) medium. It also can produce more siderophore and indole-3-acetic acid (IAA) as the concentration of iron ions decreased. However, it is unclear that the relationship between siderophore and IAA in promoting plant growth. Both Trichoderma asperellum Q1 and siderophore promotes not only the DR5::GFP transgenic Arabidopsis thaliana seedlings, in which the root IAA is labeled by green fluorescent protein gene, but also increases the content of endogenous IAA in the roots, which was shown by the fluorescence study. The strongest fluorescence was observed in the treated group inoculated with Trichoderma asperellum Q1 under the condition of insoluble iron. In the case of iron-free medium, adding siderophore also increased the observed fluorescence intensity. These results suggest that the siderophores produced by Trichoderma asperellum Q1 increased the content of IAA in Arabidopsis roots by enhancing the conversion of poorly soluble iron or by the siderophore itself.

Catecholamine oxidation-mediated transcriptional inhibition in Mn neurotoxicity.

Manganese (Mn) poisoning may result in a neurological disorder called manganism. Although the neurotoxic mechanism of Mn is unclear, oxidative stress may be involved based on the interactions between neurotransmitter catecholamines and metals such as iron. Here, we propose a novel mechanism in which Mn oxidizes catecholamines and inhibits cellular transcription. Mn accelerated the oxidation of adrenaline (Ad) and produced adrenochrome (AdC) more effectively than iron. Furthermore, the oxidation of DNA bases increased when Ad, Mn, and iron were present. However, despite the absence of iron, cell viability decreased in the presence of AdC or Ad with Mn, which suggests there is another mechanism independent of oxidative DNA damage. AdC or preincubated Ad with Mn reduced mRNA synthesis in T7 RNA polymerase-driven transcription. RNA synthesis decreased in AdC-treated cells dose-dependently. These results show that Mn disrupts neuronal function via catecholamine oxidation-mediated transcriptional inhibition.

Distribution of TR2O3, P2O5 and Nb2O5 between two immiscible melts in the monazite–SiO2–NaF–Nb2O5–Fe2O3 system

Monacite-SiO2-NaF-Nb2O5-Fe2O3 system on 1200 C isotherm is characterized by a wide area of two immiscible melts: silicate and phosphate-fluoride, salt. The system is a mutual education in molten salt a new phase of rare earth double phosphates and fluoridahospital REE and Na in the composition of which is Fe and Nb. Iron has a great influence on the immiscibility of melts: in the absence of iron, the liquation area occupies 50% of the chart area, at 5% Fe2O3 - 57%, at 10% Fe2O3 - 70%. REE, P and Nb oxides are contrast distributed between the two immiscible melts. REE and P are 95% concentrated in phosphate-salt melt. Niobium is concentrated in an iron-silicate melt. In the absence of Fe2O3 in the silicate melt, the content of Nb2O5 = 4,91%, at 15,33% it = 6,89%, i.e. increased by 40%.

Potential of Gallium as an Antifungal Agent.

There are only few drugs available to treat fungal infections, and the lack of new antifungals, along with the emergence of drug-resistant strains, results in millions of deaths/year. An unconventional approach to fight microbial infection is to exploit nutritional vulnerabilities of microorganism metabolism. The metal gallium can disrupt iron metabolism in bacteria and cancer cells, but it has not been tested against fungal pathogens such as Aspergillus and Candida. Here, we investigate in vitro activity of gallium nitrate III [Ga(NO3)3] against these human pathogens, to reveal the gallium mechanism of action and understand the interaction between gallium and clinical antifungal drugs. Ga(NO3)3 presented a fungistatic effect against azole-sensitive and -resistant A. fumigatus strains (MIC50/90 = 32.0 mg/L) and also had a synergistic effect with caspofungin, but not with azoles and amphotericin B. Its antifungal activity seems to be reliant on iron-limiting conditions, as the presence of iron increases its MIC value and because we observed a synergistic interaction between gallium and iron chelators against A. fumigatus. We also show that an A. fumigatus mutant (ΔhapX) unable to grow in the absence of iron is more susceptible to gallium, reinforcing that gallium could act by disrupting iron homeostasis. Furthermore, we demonstrate that gallium has a fungistatic effect against different species of Candida ranging from 16.0 to 256.0 mg/L, including multidrug-resistant Candida auris, C. haemulonii, C. duobushaemulonii, and C. glabrata. Our findings indicate that gallium can inhibit fungal pathogens in vitro under iron-limiting conditions, showing that Ga(NO3)3 could be a potential therapy not only against bacteria but also as an antifungal drug.

The adaptive response to iron involves changes in energetic strategies in the pathogen Candida albicans.

Candida albicans is an opportunist pathogen responsible for a large spectrum of infections, from superficial mycosis to systemic diseases known as candidiasis. Its ability to grow in different morphological forms, such as yeasts or filamentous hyphae, contributes to its survival in diverse microenvironments. Iron uptake has been associated with virulence, and C. albicans has developed elaborate strategies for acquiring iron from its host. In this work, we analyze the metabolic changes in response to changes in iron content in the growth medium and compare C. albicans adaptation to the presence or absence of iron. Functional and morphological studies, correlated to a quantitative proteomic analysis, were performed to assess the specific pathways underlying the response to iron, both in the yeast and filamentous forms. Overall, the results show that the adaptive response to iron is associated with a metabolic remodeling affecting the energetic pathways of the pathogen. This includes changes in the thiol‐dependent redox status, the activity of key mitochondrial enzymes and the respiratory chain. Iron deficiency stimulates bioenergetic pathways, whereas iron‐rich condition is associated with greater biosynthetic needs, particularly in filamentous forms. Moreover, we found that C. albicans yeast cells have an extraordinary capability to adapt to changes in environmental conditions.

Biological attenuation of arsenic and nitrate in a suspended growth denitrifying-sulphidogenic bioreactor and stability check of arsenic-laden biosolids

ABSTRACT Co-occurrence of arsenic and nitrate in groundwater sources at a wide range of concentrations is reported. In this work, performance of suspended growth semi-batch reactor was assessed for co-removal of arsenic and nitrate from simulated groundwater to meet the drinking water standards in the absence of iron. The bioreactor was inoculated with mixed bacterial culture and operated in the absence of oxygen for more than 450 days under varying influent arsenate (200–800 µg/L), nitrate concentrations (50–250 mg/L), and hydraulic retention time of 3–6 days. Complete nitrate removal was observed at all tested concentrations. Arsenic removal was found to meet drinking water standards from initial concentrations and up to 600 µg/L. The extended toxicity characteristic leaching procedure leaching experiments indicated that arsenic-laden biosolids would not constitute a hazardous waste. The arsenic leaching was found to increase with an increase in dissolved oxygen and the final leachate concentrations of arsenic were below 150 µg/L. The leaching experiments suggested maintaining non-alkaline conditions for minimum arsenic release from arsenic biosolids formed under sulphidogenic conditions. This study is the first to report that nitrate and arsenic can be simultaneously removed to meet drinking standards in a suspended growth bioreactor.

Magnetite magnetosome biomineralization in Magnetospirillum magneticum strain AMB-1: A time course study

Magnetotactic bacteria are a highly studied group of diverse prokaryotes that biomineralize chains of magnetosomes, single domain, single crystal magnetic nanoparticles of magnetite or greigite, enclosed by a lipid bilayer membrane whose synthesis is under strict genetic control. In addition to characterizing the genetics and physicochemical properties of both cultured and uncultured environmental species, there have been a number of investigations using a time course approach to determine the chemical pathway of magnetite biomineralization in these organisms. In time course studies, cells of MTB are typically grown in the absence of iron so they cannot make magnetite, and then provided with iron in culture medium which initiates the biomineralization of magnetosome chains over a subsequent time period. Results from previous time course studies are not consistent with one another, differing with regard to the nature of chemical intermediates and the rate of establishment of magnetosome chains. In this work we report a time course study of Magnetospirillum magneticum strain AMB-1 over a 48h (hour) period, using transmission electron microscopy (TEM) and soft X-ray scanning transmission X-ray microscopy (STXM) at the Fe L-edge. STXM provides capability to measure X-ray absorption spectra (XAS) and map chemical species with ∼25nm spatial resolution and thus gives detailed results on the chemistry of individual particles in single cells. An evolution of the iron oxide speciation, from a more Fe(III)-rich species, possibly α-hematite (Fe2O3), to magnetite (Fe3O4), was observed in the early stages, with evidence for the presence of the Fe(III)-rich character persisting up to 24 h. The spectromicroscopy (X-ray absorption, XAS and X-ray magnetic circular dichroism, XMCD) and TEM results show that biomineralization occurs in a stepwise fashion. First, very small particles, with no measurable magnetization, are produced at different sites in the cell without significant chain formation. The Fe L3 spectra of these early stage particles typically differ from magnetite with an additional signal at 708.4 eV that is consistent with α-hematite. By 6–8h the particles are more numerous, partial chain formation is evident, and the L3 spectrum is very similar to that of magnetite. By 24 h particles-in-chains are the dominant motif and magnetism with the moment along the chain is established. By 48 h the cells are essentially the same as cells grown in Fe-rich medium.

OmpW is positively regulated by iron via Fur, and negatively regulated by SoxS contribution to oxidative stress resistance in Escherichia coli

Iron plays a central role at the interface of pathogen and host. The ability to sequester iron from a host not only reduces host immune defenses but also promotes pathogen virulence, leading to the occurrence of infectious disease. Recently, outer membrane protein OmpW was shown to protect bacteria against harsh environmental conditions and to play a role in infectious disease. The expression of this versatile protein is controlled by iron, but the underlying mechanism of iron regulation has not been elucidated. In this study, the relation between OmpW expression and iron was investigated. Our results demonstrated that expression of OmpW is responsive to iron. Iron uptake analysis showed that an ompW mutant strain has a strong requirement for iron as compared to wild type and the ompW complemented strain. Moreover, ferric uptake regulation protein Fur, an iron binding transcriptional factor, was downregulated under iron limitation conditions and had a similar expression profile to OmpW in the presence or absence of iron. Based on these results, we suggest that iron regulates OmpW by binding to Fur. Furthermore, SoxS, a transcriptional factor involved in oxidative stress, was found to negatively regulate OmpW. We found that downregulating or knocking out OmpW results in bacterial resistance to oxidative stress. These findings provide new insight into the regulation of OmpW expression by iron, and may represent a new mechanism contributing to iron-mediated infectious disease.