Non-iron Metal Research Articles

Non-classical roles of bacterial siderophores in pathogenesis.

Within host environments, iron availability is limited, which instigates competition for this essential trace element. In response, bacteria produce siderophores, secondary metabolites that scavenge iron and deliver it to bacterial cells via specific receptors. This role in iron acquisition contributes significantly to bacterial pathogenesis, thereby designating siderophores as virulence factors. While prior research has primarily focused on unravelling the molecular mechanisms underlying siderophore biosynthesis, uptake, and iron sequestration, recent investigations have unveiled additional non-iron chelating functions of siderophores. These emerging roles are being consistently shown to support bacterial pathogenesis. In this review, we present the current understanding of siderophores in various roles: acquiring non-iron metal ions, supporting tolerance to metal-induced and reactive oxygen species (ROS)-induced stresses, mediating siderophore signalling, inducing ROS formation, and functioning in class IIb microcins. By integrating recent findings, this review aims to provide an overview of the diverse roles of siderophores in bacterial pathogenesis.

Imaging and Quantifying the Endocytosis of IRON-REGULATED TRANSPORTER1 from Arabidopsis.

Iron plays an essential role in plant metabolism and the regulation of its transport is essential for the plant. In Arabidopsis thaliana, iron uptake in root epidermal cells is mediated by the IRT1 (IRON-REGULATED TRANSPORTER 1) broad-spectrum transporter. The regulation of the IRT1 protein is controlled by sophisticated mechanisms that allow it to fine-tune the amount of transporter found at the plasma membrane and to modulate the uptake of iron and divalent metals transported by IRT1. IRT1 shows low selectivity and transports different metals such as manganese, zinc, cobalt, and cadmium. An excess of these non-iron metal substrates of IRT1 is toxic for the plant. The ability of plants to adapt to non-iron metal stress is based on the sensing of their excess, leading to the internalization and degradation of IRT1. IRT1 acts as a bifunctional transporter/receptor directly sensing metal non-iron excess and then undergoes a series of post-translational modifications of the protein culminating in its endocytosis and vacuolar degradation. To monitor the intracellular dynamics of IRT1, we describe in this chapter a live cell imaging approach to follow and quantify IRT1-mCitrine trafficking from the plasma membrane to the vacuole.

Birth, life and death of the Arabidopsis IRT1 iron transporter: the role of close friends and foes.

IRT1 intracellular dynamics and function are finely controlled through protein-protein interactions. In plants, iron uptake from the soil is tightly regulated to allow optimal growth and development. Iron acquisition in Arabidopsis root epidermal cells requires the IRT1 transporter, which also mediates the entry of non-iron metals. In this mini-review, we describe how protein-protein interactions regulate IRT1 intracellular dynamics and IRT1-mediated metal uptake to maintain iron homeostasis. Recent interactomic data provided interesting clues on IRT1 secretion and the putative involvement of COPI- and COPII-mediated pathways. Once delivered to the plasma membrane, IRT1 can interact with other components of the iron uptake machinery to form an iron acquisition complex that likely optimizes iron entrance in root epidermal cells. Then, IRT1 may be internalized from the plasma membrane. In the past decade, IRT1 endocytosis emerged as an essential mechanism to control IRT1 subcellular localization and thus to tune iron uptake. Interestingly, IRT1 endocytosis and degradation are regulated by its non-iron metal substrates in an ubiquitin-dependent manner, which requires a set of interacting-proteins including kinases, E3 ubiquitin ligases and ESCRT complex subunits. This mechanism is essential to avoid non-iron metal overload in Arabidopsis when the iron is scarce.

Regulation of Root Nutrient Transporters by CIPK23: 'One Kinase to Rule Them All'.

Protein kinases constitute essential regulatory components in the majority of cellular processes in eukaryotic cells. The CBL-INTERACTING PROTEIN KINASE (CIPK) family of plant protein kinases functions in calcium (Ca2+)-related signaling pathways and is therefore involved in the response to a wide variety of signals in plants. By covalently linking phosphate groups to their target proteins, CIPKs regulate the activity of downstream targets, their localization, their stability and their ability to interact with other proteins. In Arabidopsis, the CIPK23 kinase has emerged as a major hub driving root responses to diverse environmental stresses, including drought, salinity and nutrient imbalances, such as potassium, nitrate and iron deficiencies, as well as ammonium, magnesium and non-iron metal toxicities. This review will chiefly report on the prominent roles of CIPK23 in the regulation of plant nutrient transporters and on the underlying molecular mechanisms. We will also discuss the different scenarios explaining how a single promiscuous kinase, such as CIPK23, may convey specific responses to a myriad of signals.

Treatment of simulated electroplating wastewater containing Ni(II)-EDTA by Fenton oxidation combined with recycled ferrite process under ambient temperature.

Developing low cost and efficient method for the treatment of electroplating wastewater containing heavy metals complexed with chelating agent has attracted increasing attention in industrial wastewater treatment. This study involved a system combining Fenton oxidation (FO) and recycled ferrite (RF) process for treating synthetic solution containing Ni(II)-EDTA at ambient temperature. In this system, the FO reaction can produce hydroxyl radicals with high redox potential to decomplex the metal-organic complexes and degrade the organics, thereby enhancing the removal efficiency of heavy metals. The RF process is to incorporate the non-iron metal into the spinel ferrites at room temperature, and stabilize the sludge. As a result, the toxicity characteristic leaching procedure can fulfill the relevant standards. Furthermore, the ferrous ions in Fenton reaction could be used as the source of irons in RF process. After treatment by the combined process, the effluent water fulfills the relevant standard in China. In comparison with conventional alkaline precipitation, the sludge sedimentation velocity of FO-RF is 2.16 times faster than that of conventional alkaline precipitation and the volume of sludge is reduced by half, which strongly demonstrated the advantages of the presented FO-RF system and indicated the huge potential for the treatment of EDTA-chelated nickel.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview.

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton’s process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.

Binding of Cm(III) and Th(IV) with Human Transferrin at Serum pH: Combined QM and MD Investigations.

Human serum transferrin (sTf) can also function as a noniron metal transporter since only 30% of it is typically saturated with a ferric ion. While this function of sTf can be fruitfully utilized for targeted delivery of certain metal therapeutics, it also runs the risk of trafficking the lethal radionuclides into cells. A large number of actinide (An) ions are known to bind to the iron sites of sTf although molecular-level understanding of their binding is unclear. Understanding the radionuclide interaction with sTf is a primary step toward future design of their decorporating agents since irrespective of the means of contamination, the radionuclides are absorbed and transported by blood before depositing into target organs. Here, we report an extensive multiscale modeling approach of two An (curium(III) and thorium(IV)) ions' binding with sTf at serum physiological pH. We find that sTf binds both the heavy ions in a closed conformation with carbonate as synergistic anions and the An-loaded sTf maintains its closed conformation even after 100 ns of equilibrium molecular dynamics (MD) simulations. MD simulations are performed in a polarizable water environment, which also incorporates electronic continuum corrections for ions via charge rescaling. The molecular details of the An coordination and An exchange free energies with iron in the interdomain cleft of the protein are evaluated through a combination of quantum mechanical (QM) and MD studies. In line with reported experimental observations, well-tempered metadynamics results of the ions' binding energetics show that An-sTf complexes are less stable than Fe-sTf. Additionally, curium(III) is found to bind more weakly than thorium(IV). The latter result might suggest relative attenuation of thorium(IV) cytotoxicity when compared with curium(III).

Metal Sensing by the IRT1 Transporter-Receptor Orchestrates Its Own Degradation and Plant Metal Nutrition

Plant roots forage the soil for iron, the concentration of which can be dramatically lower than those needed for growth. Soil iron uptake uses the broad metal spectrum IRT1 transporter that also transports zinc, manganese, cobalt, and cadmium. Sophisticated iron-dependent transcriptional regulatory mechanisms allow plants to tightly control the abundance of IRT1, ensuring optimal absorption of iron. Here, we uncover that IRT1 acts as a transporter and receptor (transceptor), directly sensing excess of its non-iron metal substrates in the cytoplasm, to regulate its own degradation. Direct metal binding to a histidine-rich stretch in IRT1 triggers its phosphorylation by the CIPK23 kinase and facilitates the subsequent recruitment of the IDF1 E3 ligase. CIPK23-driven phosphorylation and IDF1-mediated lysine-63 polyubiquitination are jointly required for efficient endosomal sorting and vacuolar degradation of IRT1. Thus, IRT1 directly senses elevated non-iron metal concentrations and integrates multiple substrate-dependent regulations to optimize iron uptake and protect plants from highly reactive metals.

Mathematical model of the crystallizing blank`s thermal state at the horizontal continuous casting machine

Present article is devoted to the development of the mathematical model, which describes thermal state and crystallization process of the rectangular cross-section blank while continious process of extraction from a horysontal continious casting machine (HCCM).The developed model took cue for the heat-transfer properties of non-iron metal teeming; its temperature on entry to the casting mold; cooling conditions of blank in the carbon molds in the presence of a copper water cooler. Besides, has been considered the asymmetry of heat interchange from blank`s head and drag at mold, coming out from fluid contraction and features of the horizontal casting mold. The developed mathematical model allows to determine alterations in crystallizing blank of the following factors with respect to time: temperature pattern of crystallizing blank under different technical working regimes of HCCM; boundaries of solid two-phase field and liquid two-phase filed; blank`s thickness variation under shrinkage of the ingot`s material

Metal selectivity by the virulence-associated yersiniabactin metallophore system.

Uropathogenic Escherichia coli secrete siderophores during human infections. Although siderophores are classically defined by their ability to bind iron(III) ions, the virulence-associated siderophore yersiniabactin was recently found to bind divalent copper ions during urinary tract infections. Here we use a mass spectrometric approach to determine the extent of non-iron(III) metal interactions by yersiniabactin and its TonB-dependent outer membrane importer FyuA. In addition to copper, iron and gallium ions, yersiniabactin was also observed to form stable nickel, cobalt, and chromium ion complexes. In E. coli, copper(II) and all other non-iron(III) yersiniabactin complexes were imported by FyuA in a TonB-dependent manner. Among metal-yersiniabactin complexes, copper(II) yersiniabactin is predicted to be structurally distinctive and was the only complex not to competitively inhibit iron(III) yersiniabactin import. These results are consistent with yersiniabactin as part of a metallophore system able to prioritize iron(III) complex uptake in high copper environments.

Low-temperature growth of bamboo-like multi-walled carbon nanotubes over an atomic layer epitaxy-Cu/SiO2catalystvia metal-support interaction

The well-controlled growth of carbon nanotubes (CNTs) at low temperature (< 1073 K) using non-iron group metal catalysts remains a challenge. Here, we report that CNTs can be grown at 773–1173 K over an atomic layer epitaxy (ALE) prepared copper catalyst (ALE-Cu/SiO2) using chemical vapour deposition in helium diluted ethylene. At the same reaction conditions, only amorphous carbon can be generated over an impregnation (IM) method prepared copper catalyst (IM-Cu/SiO2). A metal-support interaction (MSI) model is proposed to describe the interaction between the ALE prepared Cu nanoparticles (NPs) and SiO2 support through the results of temperature programmed reduction profiles, X-ray photoelectron spectra and in situ X-ray diffraction (XRD) patterns. Structurally stabilised CuNPs in ALE-Cu/SiO2 catalyst indicate that the strong MSI site of CuNPs and/or copper silicide (Cu3Si) evidenced by in situ XRD patterns would be the active centers to fabricate CNTs. Our observations provide new insights into controlling the CNT growth at low-temperatures over non-ferromagnetic catalysts.

Structural Decomposition Analysis of Raw Material Consumption

Summary The aim of this article is to quantify the drivers for the changes in raw material consumption (domestic material consumption expressed in the form of all materials extracted and used in the production phase) in terms of technology, which refers to the concept of sustainable production; the product structure of final demand, which refers to the concept of sustainable consumption; and the volume of final demand, which is related to economic growth. We also aim to determine to what extent the technological development and a shift in product structure of the final demand compensate for the growth in final consumption volume. Therefore, we apply structural decomposition analysis (SDA) to the change in raw material consumption (RMC) of the Czech Republic between 2000 and 2007. To present the study in a broader context, we also show other material flow indicators for the Czech Republic for 2000 and 2007. Our findings of SDA show that final demand structure has a very limited effect on the change in material flows. The rapid change in final demand volume was not compensated for crude oil, metal ores, construction materials, food crops, and timber. For the material category of non-iron metal ores, even the change in technology contributes to an increase in material flows. The largest relative increases are reported for non-iron metal ores (38%) and construction materials (30%). The main changes in material flows related to the Czech Republic are driven by exports and enabled by imports, the main source of these increased material flows. This emphasizes the increasing role of international trade.

Chemical stability and extent of isomorphous substitution in ferrites precipitated under ambient temperatures

The ferrite process is an established method for treating wastewaters containing dissolved toxic metals, using precipitation at temperatures above 65 °C. Various ambient-temperature operation methodologies have also been proposed, but the effects of temperature reduction on product stability, and on the extent of isomorphous substitution (in terms of x in Me x Fe 3− x O 4, Me representing a non-iron metal), have not been adequately quantified. At ambient temperature precipitation, maximal x of Zn 2+, Co 2+, Ni 2+ and Cd 2+ was found in the current study to be approximately 0.73, 0.67, 0.39 and 0.17, respectively. These values are 73% to 50% of the corresponding values attained by precipitation at 90 °C. The chemical stability of the ferrites produced under ambient temperatures was found to deteriorate upon high Me 2+ incorporation levels, in stark contrast with the trend observed in ferrites precipitated at 90 °C. Both observations were ascribed to the increased importance of Fe 2+–Fe 3+ interaction under ambient conditions in driving spinel ordering. In the presence of high Me to Fe ratio in the initial solution, this interaction is weaker, resulting in impeded dehydration.

Extent and mechanism of metal ion incorporation into precipitated ferrites

The ability of many noniron metals to be incorporated into the structure of ferrites is being utilized in numerous industrial and environmental applications. The incorporation of some of these metals during Fe(II) oxidation-induced precipitation at moderate temperatures (80–100 °C) appears to be limited, for reasons not fully understood, and to extents not always agreed (e.g., Ni 2+, Cr 3+). In this paper, the incorporation maxima of six metals into the structure of precipitated ferrites (in terms of x in Me x Fe 3− x O 4, Me represents a noniron metal) were concluded to be 1.0, 1.0, 0.78, 0.49, 0.35, and 0.0 for Zn 2+, Co 2+, Ni 2+, Al 3+, Cd 2+ and Cr 3+, respectively. With the exception of the much larger Cd 2+, these values were associated with kinetic considerations controlled by the H 2O exchange rate between the hydration shells surrounding the dissolved metal ion.

The role of denitrification on arsenite oxidation and arsenic mobility in an anoxic sediment column model with activated alumina

Arsenite (As(III)) is the predominant arsenic (As) species in reducing environments. As(III) is less strongly adsorbed than As(V) at circumneutral pH conditions by common non-iron metal oxides in sediments such as those of aluminum. Therefore, oxidation of As(III) to As(V) could contribute to an improved immobilization of As and thus help mitigate As contamination in groundwater. Microbial oxidation of As(III) is known to readily under aerobic conditions, however, the dissolved oxygen (O₂) concentration in groundwater may be limited due to the poor solubility of O₂ and its high chemical reactivity with reduced compounds. Nitrate (NO₃⁻), can be considered as an alternative electron acceptor, which can support oxidation of As(III) to As(V) by denitrifying bacteria. In this study, two up-flow sediment columns packed with activated alumina (AA) were utilized to demonstrate the role of denitrification on the oxidation of As(III) to As(V) and its contribution to improved As adsorption onto AA. One column was supplied with NO₃⁻(C1) and its performance was compared with a control column lacking NO₃⁻(C2). During most of the operation when the pH was in the circumneutral range (days 50-250), the release of arsenic was greater from C2 compared to C1. The effluent As concentrations started increasing on days 60 and 100 in C2 and C1, respectively. Complete breakthrough started on day 200 in C2; whereas in C1, complete breakthrough was never achieved. The effluent and solid phase As speciation was dominated by As(V) in C1, indicating the occurrence of As(III) oxidation due to NO₃⁻; whereas in C2, only As(III) was dominant. This study illustrates a bioremediation or natural attenuation process based on anoxic microbial NO₃⁻-dependent oxidation of As(III) to more readily adsorbed As(V) as a means to enhance the immobilization of As on alumina oxide particles in subsurface environments.

Active Cystathionine β-Synthase Can Be Expressed in Heme-free Systems in the Presence of Metal-substituted Porphyrins or a Chemical Chaperone

Cystathionine beta-synthase (CBS), a key enzyme in the metabolism of homocysteine, has previously been shown to require a heme co-factor for maximal activity. However, the biochemical function of the CBS heme is not well defined. Here, we show that expression of human CBS in heme-deficient strains of Saccharomyces cerevisiae and Escherichia coli results in production of an enzyme that is misfolded and degraded. Addition of exogenous heme, porphyrins with non-iron metal, or porphyrin lacking metal entirely produced stable and active CBS enzyme. Purification of recombinant CBS enzyme expressed in the presence of various metalloporphyrins confirmed that Mn(III) and Co(III) had 30-60% of the specific activity of Fe(III)-CBS, and still responded to allosteric activation by S-adenosyl-L-methionine. Treatment of S. cerevisiae with the chemical chaperone trimethylamine-N-oxide resulted in near complete restoration of function to human CBS produced in a heme-deficient strain. Taken together, these results suggest that porphyrin moiety of the heme plays a critical role in proper CBS folding and assembly, but that the metal ion is not essential for this function or for allosteric regulation by S-adenosyl-L-methionine.

A New Type of Metalloprotein: The Mo Storage Protein from Azotobacter vinelandii Contains a Polynuclear Molybdenum–Oxide Cluster

Azotobacter vinelandii is a diazotrophic bacterium characterized by the outstanding capability of storing Mo in a special storage protein, which guarantees Mo-dependent nitrogen fixation even under growth conditions of extreme Mo starvation. The Mo storage protein is constitutively synthesized with respect to the nitrogen source and is regulated by molybdenum at an extremely low concentration level (0-50 nM). This protein was isolated as an alpha4beta4 octamer with a total molecular mass of about 240 kg mol(-1) and its shape was determined by small-angle X-ray scattering. The genes of the alpha and beta subunits were unequivocally identified; the amino acid sequences thereby determined reveal that the Mo storage protein is not related to any other known molybdoprotein. Each protein molecule can store at least 90 Mo atoms. Extended X-ray absorption fine-structure spectroscopy identified a metal-oxygen cluster bound to the Mo storage protein. The binding of Mo (biosynthesis and incorporation of the cluster) is dependent on adenosine triphosphate (ATP); Mo release is ATP-independent but pH-regulated, occurring only above pH 7.1. This Mo storage protein is the only known noniron metal storage system in the biosphere containing a metal-oxygen cluster.

Oxygen binding by alpha(Fe2+)2beta(Ni2+)2 hemoglobin crystals.

Oxygen binding by hemoglobin fixed in the T state either by crystallization or by encapsulation in silica gels is apparently noncooperative. However, cooperativity might be masked by different oxygen affinities of alpha and beta subunits. Metal hybrid hemoglobins, where the noniron metal does not bind oxygen, provide the opportunity to determine the oxygen affinities of alpha and beta hemes separately. Previous studies have characterized the oxygen binding by alpha(Ni2+)2beta(Fe2+)2 crystals. Here, we have determined the three-dimensional (3D) structure and oxygen binding of alpha(Fe2+)2beta(Ni2+)2 crystals grown from polyethylene glycol solutions. Polarized absorption spectra were recorded at different oxygen pressures with light polarized parallel either to the b or c crystal axis by single crystal microspectrophotometry. The oxygen pressures at 50% saturation (p50s) are 95 +/- 3 and 87 +/- 4 Torr along the b and c crystal axes, respectively, and the corresponding Hill coefficients are 0.96 +/- 0.06 and 0.90 +/- 0.03. Analysis of the binding curves, taking into account the different projections of the alpha hemes along the optical directions, indicates that the oxygen affinity of alpha1 hemes is 1.3-fold lower than alpha2 hemes. Inspection of the 3D structure suggests that this inequivalence may arise from packing interactions of the Hb tetramer within the monoclinic crystal lattice. A similar inequivalence was found for the beta subunits of alpha(Ni2+)2beta(Fe2+)2 crystals. The average oxygen affinity of the alpha subunits (p50 = 91 Torr) is about 1.2-fold higher than the beta subunits (p50 = 110 Torr). In the absence of cooperativity, this heterogeneity yields an oxygen binding curve of Hb A with a Hill coefficient of 0.999. Since the binding curves of Hb A crystals exhibit a Hill coefficient very close to unity, these findings indicate that oxygen binding by T-state hemoglobin is noncooperative, in keeping with the Monod, Wyman, and Changeux model.

Bacterial and Chemical Reductive Dissolution of Mn-, Co-, Cr-, and Al-Substituted Goethites

Goethite samples in which 5% of the iron atoms were replaced with different noniron metal (NIM) atoms (Mn, Co, Al, Cr) were synthesized and characterized by X-ray diffraction. Their dissolution (a) by bacterial (enzymatic) reduction and (b) by chemical dissolution through reduction and complexing with a citrate-bicarbonate-dithionite reagent was investigated and compared with the response of similarly treated nonsubstituted goethite. Chemical dissolution differed in rate of iron solubilization depending on NIM substituents. Initial rates of iron dissolution were faster with goethite-lacking metal substituents than with Al-goethite. Bacterial fermentation and reduction processes were not significantly modified by the presence of Mn, Co, Al, or Cr, but the dissolution rates of iron decreased with substitution. During bacterial iron reduction, Al-goethite was more resistant than Mn-goethite, Co-goethite, Cr-goethite, and pure goethite. Both chemical and bacterial reduction of iron resulted in simultaneous solubilization of the NIMs. In the chemical treatment, Mn, Al, and Co were dissolved congruently with respect to Fe, whereas Cr was not. However, in the bacterial treatment, only Mn and Co solubilization were congruent with respect to iron. The fate of the substitution metals is of fundamental interest to an understanding of microbial weathering and in assessing the potential, after solubilization, for their uptake by plants and pollution of ground water.

Flow cytometric measurement of micronuclei induced in a permanent fish cell line as a possible screening test for the genotoxicity of industrial waste waters.

An in vitro micronucleus assay using the permanent fish cell line RTG-2 (rainbow trout gonads) was developed to test industrial waste waters for their genotoxic potential. Comparison of flow cytometric measurement and microscopic scoring of micronucleus frequency with the reference chemicals 1,4-butane sultone (0.2-1 mM), ethylmethane sulphonate (2-10 mM), potassium dichromate (20-100 microM) and benzo[a]pyrene (5-25 microM) showed similar dose-effect relationships. Thirty-eight industrial waste waters from 11 different branches of industry obtained from the Bavarian state office for water research were tested using the flow cytometric method (18 from metal processing, 10 from combined waste water, two from synthetic fibre production, one sample each from settlement wastes, non-iron metal manufacturing, leather production, sulphuric acid production, ore processing, graphite film production, cellulose production and flue gas washing). Fourteen of them showed a significant increase in micronucleus frequency.