FeO System Research Articles

Transcriptomic insights into the virulence of Acinetobacter baumannii during infection-role of iron uptake and siderophore production genes.

Acinetobacter baumannii, a top-priority WHO pathogen, causes life-threatening infections in immunocompromised patients, leading to prolonged hospitalisation and high mortality. Here, we used the Galleria mellonella model to investigate community strain C98 (Ab-C98) virulence via transcriptomic analysis. Ab-C98 showed greater killing and faster colonisation in larvae than the clinical reference strain (ATCC BAA1605). Genes in three iron clusters, acinetobactin, baumannoferrin and the Feo system, were significantly up-regulated. Targeted knockout of siderophore genes (basC, bfnD, and the gene encoding isochorismatase) significantly increased the survival of infected larvae by at least 35.16%, identifying these genes as potential targets for developing anti-virulence agents against A. baumannii.

Machine Learning Model for the Prediction of Hubbard U Parameters and Its Application to Fe-O Systems.

Without incurring additional computational cost, the Hubbard model can prevalently address the electron self-interaction problems of the local or semilocal exchange-correlation functions within density functional theory. However, determining the value of the Hubbard parameter, U, promptly, efficiently, and accurately has been a long-standing challenge. Here, we develop a method for predicting the Hubbard U of iron oxides by establishing a potential relationship through machine learning fitting of structural fingerprints and the U evaluated by the linear response-constrained density functional theory method. This method performs well in calculating the properties of wüstite, hematite, and magnetite, aligning with experimental measurements or more costly hybrid functional results. Using this method, we redefine the convex hulls of the Fe-O system at 0, 50, and 100 GPa; the obtained results are in good agreement with experimental observations. We also provide insights into the debates surrounding the high-pressure phases of Fe2O3 and Fe3O4.

Potential Utilization of Iron Oxidation Reaction Heat for the Generation of SiO2–FeO System Melts

Silicon-containing steel forms an oxide layer within the scale during hot rolling. This layer comprising oxides such as Fe2SiO4 and FeO adversely affect the surface quality of steel owing to strong adhesion between Fe2SiO4 and the steel substrate. A method to melt this silicon-containing oxide layer through the oxidation reaction of iron plates by applying SiO2 powder to the surface is proposed. The aim of this study is to understand the reaction mechanism and identify the optimal conditions for this process. Application of SiO2 coating to the surface of an iron plate at 6.67 × 10–4 g·mm−2 and maintaining the plate at 1423 K, just below the eutectic temperature of Fe2SiO4–FeO system (1450 K), cause the surface oxide scale to melt when exposed to oxidation in an atmospheric environment. Notably, reducing the electric furnace temperature hinders the melting process, whereas excessive application of SiO2 hampers the formation of sufficient liquid phase. On the surface of the iron plate, primarily FeO and Fe2SiO4 are formed. Heat generation is mainly due to the formation of FeO, which leads to the rapid generation of Fe2SiO4. Eutectic reactions within SiO2–Fe2SiO4 or FeO–Fe2SiO4 systems drive the formation of the liquid phase. Once the liquid phase was established, rapid diffusion of iron ions within it resulted in rapid iron oxidation and additional heat generation. Ultimately, a liquid phase in equilibrium with FeO is formed across the entire surface of the iron plate.

Analysis of phase equilibria in liquid chromium-manganese steels in the presence of calcium. Report 1. Phase diagrams of oxide systems.

The metallurgical industry produces a wide range of chromium-manganese steels, deoxidized and modified with calcium. To determine the non-metallic inclusions (NI) that can form in the Fe–Ca–Cr–Mn–C–O system, it is necessary to study the double and triple phase diagrams included in the FeO–CaO–MnO–Cr2O3 system. Divalent chromium oxide, which is also included in the oxide melt in the Fe–Ca–Cr–Mn–C–O system, practically does not occur in the literature as a component of double or triple state diagrams; therefore, the activity of chromium(II) oxide was equated to its ion fraction and state diagrams with it were not considered in this work. The state diagrams of oxide systems FeO–CaO, FeO–MnO, FeO–Cr2O3, CaO–MnO, MnO–Cr2O3, and FeO–MnO–Cr2O3 were previously studied by the authors. In this work, the state diagrams of the CaO–Cr2O3, FeO–CaO–Cr2O3, FeO–CaO–MnO, and CaO–MnO–Cr2O3 systems are calculated and plotted. The mixing energies are selected to determine activities in solid (theory of regular ionic solutions) and liquid (theory of subregular ionic solutions) oxide solutions to calculate the coordinates of the liquidus and solidus lines of these state diagrams. The enthalpy (103.4 KJ/mol) and entropy (21.958 J/(mol•K)) of melt-ing of calcium chromite CaCr2O4 are specified. The invariant points of the state diagrams of the FeO–CaO–Cr2O3 and CaO–MnO–Cr2O3 systems have been determined. The study of double and triple phase diagrams belonging to the FeO–CaO–MnO–Cr2O3 system will make it possible to determine all possible NIs that can form in chromium-manganese steels in the presence of calcium under equilibrium conditions.

Effect of Fe-O ReaxFF on Liquid Iron Oxide Properties Derived from Reactive Molecular Dynamics.

As iron powder nowadays attracts research attention as a carbon-free, circular energy carrier, molecular dynamics (MD) simulations can be used to better understand the mechanisms of liquid iron oxidation at elevated temperatures. However, prudence must be practiced in the selection of a reactive force field. This work investigates the influence of currently available reactive force fields (ReaxFFs) on a number of properties of the liquid iron-oxygen (Fe-O) system derived (or resulting) from MD simulations. Liquid Fe-O systems are considered over a range of oxidation degrees ZO, which represents the molar ratio of O/(O + Fe), with 0 < ZO < 0.6 and at a constant temperature of 2000 K, which is representative of the combustion temperature of micrometric iron particles burning in air. The investigated properties include the minimum energy path, system structure, (im)miscibility, transport properties, and the mass and thermal accommodation coefficients. The properties are compared to experimental values and thermodynamic calculation results if available. Results show that there are significant differences in the properties obtained with MD using the various ReaxFF parameter sets. Based on the available experimental data and equilibrium calculation results, an improved ReaxFF is required to better capture the properties of a liquid Fe-O system.

Microbial iron acquisition is influenced by spatial and temporal conditions in a glacial influenced river and estuary system.

In Arctic regions, glaciers are major sources of iron to rivers and streams; however, estuaries are considered iron sinks due to the coagulation and flocculation processes that occur at higher salinities. It is unknown how iron dynamics in a glacial influenced river and estuary environment affect microbial mechanisms for iron acquisition. Microbial taxonomic and functional sequencing was performed on samples taken throughout the year from the Kenai River and the estuary, Alaska. Despite distinct iron, sodium, and other nutrient concentrations, the river and estuary did not have statistically different microbial communities nor was time of sampling significant. However, ferrous iron transport (Feo) system genes were more abundant in river environments, while siderophore genes were more abundant and diverse in estuary environments. Siderophore transport and iron storage genes were found in all samples, but gene abundance and distribution were potentially influenced by physical drivers such as discharge rates and nutrient distributions. Differences in iron metabolism between river and estuary ecosystems indicate environmental conditions drive microbial mechanisms to sequester iron. This could have implications for iron transport as the Arctic continues to warm.

Divide and conquer: genetics, mechanism, and evolution of the ferrous iron transporter Feo in Helicobacter pylori.

Feo is the most widespread and conserved system for ferrous iron uptake in bacteria, and it is important for virulence in several gastrointestinal pathogens. However, its mechanism remains poorly understood. Hitherto, most studies regarding the Feo system were focused on Gammaproteobacterial models, which possess three feo genes (feoA, B, and C) clustered in an operon. We found that the human pathogen Helicobacter pylori possesses a unique arrangement of the feo genes, in which only feoA and feoB are present and encoded in distant loci. In this study, we examined the functional significance of this arrangement. Requirement and regulation of the individual H. pylori feo genes were assessed through in vivo assays and gene expression profiling. The evolutionary history of feo was inferred via phylogenetic reconstruction, and AlphaFold was used for predicting the FeoA-FeoB interaction. Both feoA and feoB are required for Feo function, and feoB is likely subjected to tight regulation in response to iron and nickel by Fur and NikR, respectively. Also, we established that feoA is encoded in an operon that emerged in the common ancestor of most, but not all, helicobacters, and this resulted in feoA transcription being controlled by two independent promoters. The H. pylori Feo system offers a new model to understand ferrous iron transport in bacterial pathogens.

Functional Characterization of FeoAB in Iron Acquisition and Pathogenicity in Riemerella anatipestifer.

The bacterium Riemerella anatipestifer requires iron for growth, but the mechanism of iron uptake is not fully understood. In this study, we disrupted the Feo system and characterized its function in iron import in R. anatipestifer ATCC 11845. Compared to the parent strain, the growth of the ΔfeoA, ΔfeoB, and ΔfeoAB strains was affected under Fe3+-limited conditions, since the absence of the feo system led to less intracellular iron than in the parent strain. In parallel, the ΔfeoAB strain was shown to be less sensitive to streptonigrin, an antibiotic that requires free iron to function. The sensitivity of the ΔfeoAB strain to hydrogen peroxide was also observed to be diminished compared with that of the parent strain, which could be related to the reduced intracellular iron content in the ΔfeoAB strain. Further research revealed that feoA and feoB were directly regulated by iron through the Fur regulator and that the transcript levels of feoA and feoB were significantly increased in medium supplemented with 1 mM MnCl2, 400 μM ZnSO4, and 200 μM CuCl2. Finally, it was shown that the ΔfeoAB strain of R. anatipestifer ATCC 11845 was significantly impaired in its ability to colonize the blood, liver, and brain of ducklings. Taken together, these results demonstrated that FeoAB supports ferrous iron acquisition in R. anatipestifer and plays an important role in R. anatipestifer colonization. IMPORTANCE In Gram-negative bacteria, the Feo system is an important ferrous iron transport system. R. anatipestifer encodes an Feo system, but its function unknown. As iron uptake may be required for oxidative stress protection and virulence, understanding the contribution of iron transporters to these processes is crucial. This study showed that the ΔfeoAB strain is debilitated in its ability to import iron and that its intracellular iron content was constitutively low, which enhanced the resistance of the deficient strain to H2O2. We were surprised to find that, in addition to responding to iron, the Feo system may play an important role in sensing manganese, zinc, and copper stress. The reduced colonization ability of the ΔfeoAB strain also sheds light on the role of iron transporters in host-pathogen interactions. This study is important for understanding the cross talk between iron and other metal transport pathways, as well as the pathogenic mechanism in R. anatipestifer.

FeoC from Klebsiella pneumoniae uses its iron sulfur cluster to regulate the GTPase activity of the ferrous iron channel

Bacteria depend on the ferrous iron transport (Feo) system for the uptake of ferrous iron (Fe2+). The Feo system is crucial for colonization and virulence of pathogens. In γ-proteobacteria, the system consists of FeoA, FeoB, and FeoC. The function of FeoA remains unknown. FeoB likely forms the channel, whose regulation has been suggested to involve its GTPase domain (part of its NFeoB domain). FeoC from Klebsiella pneumonia was found to contain a [4Fe4S] cofactor, whose presence was speculated to enhance the GTPase activity of FeoB (Hsueh, K.-L., et al., J. Bacteriol. 2013 195(20): 4726–34). We present results here that support and extend that hypothesis. We monitored the GTPase activity of FeoB by NMR spectroscopy and found that the presence of 7% FeoC-[4Fe-4S]3+ (the highest level of cofactor achieved in vitro) increased the GTPase rate of NFeoB by 3.6-fold over NFeoB. The effect depends on the oxidation state of the cluster; with reduction of the cluster to [4Fe-4S]2+ the GTPase greatly decreased the GTPase rate. From the effects of point mutations in FeoC on GTPase rates, we conclude that Lys62 and Lys68 on FeoC each contribute to increased GTPase activity on NFeoB. Mutation of Thr37 of NFeoB to Ser nearly abolished the GTPase activity. The GTPase activity of the isolated K. pneumoniae NFeoB-FeoC complex (NFeoBC) was found to be higher in KCl than in NaCl solution. We solved the X-ray structure of the NFeoBC crystallized from KCl and compared it with a prior X-ray structure crystalized from NaCl. We propose a hypothesis, consistent with these results, to explain the factors that influence the GTPase activity. Bacteria may use the oxygen-sensitive cluster as a sensor to up-regulate the gate closing speed.

Y2O3‒SiO2 SYSTEM DIAGRAM

The deoxidizing ability of yttrium has not been sufficiently studied, although it has a high affinity for oxygen. In ferrous metallurgy, yttrium is often used in the form of an alloy with silicon. The effect of each of the components of the silicoyttrium alloy on the process of liquid metal deoxidation can be established by studying the Fe‒Y‒Si‒O system. The composition of the formed non-metallic inclusions in steel in this case is mainly determined by the type of oxide state diagrams of the Y2O3‒SiO2 and FeO‒Y2O3‒SiO2 systems associated with the region of existence of metallic melts. In this work, using the method of thermodynamic modeling of phase equilibrium in oxide system state diagrams and the theory of subregular ionic solutions, we analyze and calculate liquidus lines in the Y2O3‒SiO2 oxide system. A diagram of the state of this system was constructed. According to the thermodynamic analysis, the most stable in the system are three compounds ‒ oxy- Y2O3·SiO2 and yttrium orthosilicate 2Y2O3·3SiO2 (congruent melting, 1979 and 1915 °C, respectively), as well as yttrium pyrosilicate Y2O3·2SiO2 (incongruent melting), which is consistent with the literature data. In the course of the work, the enthalpies and entropies of formation of these yttrium silicates from the components of the oxide melt, as well as the melting constants of these compounds, were obtained. The area of delamination borders on the field of cristobalite at 1668 °C in the concentration range 0.593‒0.980 (ionic fraction of SiO2) or 74.5‒99.0 % (mol.) SiO2. The values of the enthalpy and entropy of yttrium silicates obtained in this work allow us to proceed to the next stage of the study – modeling the state diagram of the ternary oxide system FeO‒Y2O3‒SiO2, which is necessary to consider the interaction of yttrium and silicon with oxygen in liquid iron.

The structure of Vibrio cholerae FeoC reveals conservation of the helix-turn-helix motif but not the cluster-binding domain.

Most pathogenic bacteria require ferrous iron (Fe2+) in order to sustain infection within hosts. The ferrous iron transport (Feo) system is the most highly conserved prokaryotic transporter of Fe2+, but its mechanism remains to be fully characterized. Most Feo systems are composed of two proteins: FeoA, a soluble SH3-like accessory protein, and FeoB, a membrane protein that translocates Fe2+ across a lipid bilayer. Some bacterial feo operons encode FeoC, a third soluble, winged-helix protein that remains enigmatic in function. We previously demonstrated that selected FeoC proteins bind O2-sensitive [4Fe-4S] clusters via Cys residues, leading to the proposal that some FeoCs could sense O2 to regulate Fe2+ transport. However, not all FeoCs conserve these Cys residues, and FeoC from the causative agent of cholera (Vibrio cholerae) notably lacks any Cys residues, precluding cluster binding. In this work, we determined the NMR structure of VcFeoC, which is monomeric and conserves the helix-turn-helix domain seen in other FeoCs. In contrast, however, the structure of VcFeoC reveals a truncated winged β-sheet in which the cluster-binding domain is notably absent. Using homology modeling, we predicted the structure of VcNFeoB and used docking to identify an interaction site with VcFeoC, which is confirmed by NMR spectroscopy. These findings provide the first atomic-level structure of VcFeoC and contribute to a better understanding of its role vis-à-vis FeoB.

P–T–X (Fe–Mg) Relations of Cummingtonite-sillimanite-cordieritequartz-H2O Equilibrium: Implications on Evolution of Metamorphic Rocks

Abstract The P–T–X (Fe–Mg) phase relations of the cummingtonitesillimanite-cordierite-quartz-fluid assemblage have been constructed considering the model system FeO–MgO–Al2O3–SiO2–H2O (FMASH) and using available experimental and thermodynamic data. The assemblage represents a divariant reaction: cum + sil+ qtz= crd + H2O, the Fe- and Mg-end member reactions of which have positive slope in P–T space. Isobaric T–X (Fe–Mg) loop and isothermal P–X (Fe–Mg) loop show that,at constant pressure, both cummingtonite and cordierite become Fericher with increasing temperature, whereas, at constant temperature, this assemblage is displaced towards Mg-richer compositions with increasing pressure. The study of the P–T–X relationships of cummingtonite-sillimanite-cordierite-quartz-H2O equilibrium suggests that the cummingtonite–cordierite bearing assemblages are stable at the low-pressure metamorphic environment.

Oxidized pellets production from stainless steel solid wastes: induration characteristics and harmful elements migration behavior

Stainless steel solid wastes (SSSW) treatment and recycling has attracted wide attention in recent years because of more stringent environment laws and regulations. Recycling of SSSW through carbothermal reduction of chromite (SRC)-electric furnace (EF) process is favorable to the effective treatment of SSSW and recovery of valuable elements. In this paper, SSSW are used to manufacture sufficiently strong oxidized pellets with the coexistence of chromite concentrates for ferrochrome production based on the SRC-EF process. The induration characteristics and harmful element migration behavior during oxidation of pellets are investigated and revealed. It is found that the oxidized pellets made from 100% SSSW possess low mechanical strength. Increasing the ratio of chromite concentrate from 0% to 80% can significantly improve the pellet strength from 460 N/pellet to 1868 N/pellet when preheating at 1000 °C for 12min and roasting at 1275 °C for 15min. Oxidized pellets made from SSSW and chromite are mainly dominated by the solid-phase consolidation due to the recrystallization of iron-rich spinel phases and sesquioxide derived from oxidation of ferrous oxides. In addition, slag bonding of CaO–CaF2–SiO2–FeO system also plays an important role in the consolidation of oxidized pellets. As for pellets made from 32% SSSW and 68% chromite concentrate, 39.96% F, 91.06% S, 66.73% Cl can be removed from the pellets when preheating at 1000 °C for 12 min and roasting at 1275 °C for 15 min.

A general protocol for the expression and purification of the intact transmembrane transporter FeoB

Ferrous iron (Fe2+) transport is an essential process that supports the growth, intracellular survival, and virulence of several drug-resistant pathogens, and the ferrous iron transport (Feo) system is the most important and widespread protein complex that mediates Fe2+ transport in these organisms. The Feo system canonically comprises three proteins (FeoA/B/C). FeoA and FeoC are both small, accessory proteins localized to the cytoplasm, and their roles in the Fe2+ transport process have been of great debate. FeoB is the only wholly-conserved component of the Feo system and serves as the inner membrane-embedded Fe2+ transporter with a soluble G-protein-like N-terminal domain. In vivo studies have underscored the importance of Feo during infection, emphasizing the need to better understand Feo-mediated Fe2+ uptake, although a paucity of research exists on intact FeoB. To surmount this problem, we designed an overproduction and purification system that can be applied generally to a suite of intact FeoBs from several organisms. Importantly, we noted that FeoB is extremely sensitive to excess salt while in the membrane of a recombinant host, and we designed a workflow to circumvent this issue. We also demonstrated effective protein extraction from the lipid bilayer through small-scale solubilization studies. We then applied this approach to the large-scale purifications of Escherichia coli and Pseudomonas aeruginosa FeoBs to high purity and homogeneity. Lastly, we show that our protocol can be generally applied to various FeoB proteins. Thus, this workflow allows for isolation of suitable quantities of FeoB for future biochemical and biophysical characterization.

Purification and functional analysis of the ferrous iron transport protein B (FeoB) incorporated into SMA‐copolymer nanodiscs

The acquisition and transport of ferrous iron (Fe2+) is essential for the survival and the virulence of many infectious prokaryotes. While bacteria possess several methods to acquire Fe2+, the ferrous iron transport (Feo) system is the most important Fe2+ transport complex with strong ties to bacterial virulence. Despite this significance, an understanding of the structure‐function relationship of the transporter FeoB is limited due to its intrinsically insoluble nature that renders it generally intractable outside of a lipid bilayer. Traditionally, detergents have been used to solubilize membrane proteins such as FeoB; however, detergent micelles can disrupt protein folding, lead to protein instability, and even inhibit important and essential protein‐protein interactions. In lieu of traditional amphipathic detergents, styrene‐maleic acid (SMA) copolymers have been demonstrated to solubilize membrane proteins into a nanodisc while encapsulating native lipids, thereby preventing protein misfolding and preserving protein‐protein interaction sites. In this work, we describe the first successful solubilization and purification of Escherichia coli FeoB (EcFeoB) in SMA nanodiscs. This approach has afforded our ability to obtain highly pure, monomeric EcFeoB‐SMA nanodiscs. In addition, we compare the NTPase activity of detergent‐solubilized EcFeoB to that of SMA‐solubilized EcFeoB nanodiscs to probe nucleotide‐hydrolysis rates in the presence of an artificial micelle compared to a lipid bilayer. This approach represents a promising first step in understanding the structure and the mechanism of the FeoB transporter in its native environment.

The fciTABC and feoABI systems contribute to ferric citrate acquisition in Stenotrophomonas maltophilia

BackgroundStenotrophomonas maltophilia, a member of γ-proteobacteria, is a ubiquitous environmental bacterium that is recognized as an opportunistic nosocomial pathogen. FecABCD system contributes to ferric citrate acquisition in Escherichia coli. FeoABC system, consisting of an inner membrane transporter (FeoB) and two cytoplasmic proteins (FeoA and FeoC), is a well-known ferrous iron transporter system in γ-proteobacteria. As revealed by the sequenced genome, S. maltophilia appears to be equipped with several iron acquisition systems; however, the understanding of these systems is limited. In this study, we aimed to elucidate the ferric citrate acquisition system of S. maltophilia.MethodsCandidate genes searching and function validation are the strategy for elucidating the genes involved in ferric citrate acquisition. The candidate genes responsible for ferric citrate acquisition were firstly selected using FecABCD of E. coli as a reference, and then revealed by transcriptome analysis of S. maltophilia KJ with and without 2,2′-dipyridyl (DIP) treatment. Function validation was carried out by deletion mutant construction and ferric citrate utilization assay. The bacterial adenylate cyclase two-hybrid system was used to verify intra-membrane protein–protein interaction.ResultsSmlt2858 and Smlt2356, the homologues of FecA and FecC/D of E. coli, were first considered; however, deletion mutant construction and functional validation ruled out their involvement in ferric citrate acquisition. FciA (Smlt1148), revealed by its upregulation in DIP-treated KJ cells, was the outer membrane receptor for ferric citrate uptake. The fciA gene is a member of the fciTABC operon, in which fciT, fciA, and fciC participated in ferric citrate acquisition. Uniquely, the Feo system of S. maltophilia is composed of a cytoplasmic protein FeoA, an inner membrane transporter FeoB, and a predicted inner membrane protein FeoI. The intra-membrane protein–protein interaction between FeoB and FeoI may extend the substrate profile of FeoB to ferric citrate. FeoABI system functioned as an inner membrane transporter of ferric citrate.ConclusionsThe FciTABC and FeoABI systems contribute to ferric citrate acquisition in S. maltophilia.

Structure and motifs of iron oxides from 1 to 3 TPa

Iron oxides are fundamental components of planet-forming materials. Understanding the Fe-O system's behavior and properties under high pressure can help us identify many new phases and states possible in exoplanetary interiors, especially terrestrial ones. Using the adaptive genetic algorithm (AGA), we investigate the structure of iron oxides for a wide range of stoichiometries ($0.25\leq x_O \leq 0.8$) at 1, 2, and 3 TPa. Five unreported ground-state structures with Fe$_2$O, FeO, Fe$_3$O$_5$, FeO$_2$, and FeO$_4$ compositions are identified. The calculated density of states (DOS) suggests that, except for FeO$_4$, all phases are metallic, but their carrier densities decrease with increasing pressure and oxygen content. The cluster alignment analysis of stable and metastable phases shows that several motifs may co-exist in a structure of iron oxides with low O content. In contrast, most iron oxides with high O content adopt a simple BCC motif at TPa pressures. Our results provide a crystal structure database of iron oxides for modeling and understanding the interiors of exoplanets.

A fusion of the Bacteroides fragilis ferrous iron import proteins reveals a role for FeoA in stabilizing GTP-bound FeoB

Iron is an essential element for nearly all organisms, and under anoxic and/or reducing conditions, Fe2+ is the dominant form of iron available to bacteria. The ferrous iron transport (Feo) system is the primary prokaryotic Fe2+ import machinery, and two constituent proteins (FeoA and FeoB) are conserved across most bacterial species. However, how FeoA and FeoB function relative to one another remains enigmatic. In this work, we explored the distribution of feoAB operons encoding a fusion of FeoA tethered to the N-terminal, G-protein domain of FeoB via a connecting linker region. We hypothesized that this fusion poises FeoA to interact with FeoB to affect function. To test this hypothesis, we characterized the soluble NFeoAB fusion protein from Bacteroides fragilis, a commensal organism implicated in drug-resistant infections. Using X-ray crystallography, we determined the 1.50-Å resolution structure of BfFeoA, which adopts an SH3-like fold implicated in protein–protein interactions. Using a combination of structural modeling, small-angle X-ray scattering, and hydrogen–deuterium exchange mass spectrometry, we show that FeoA and NFeoB interact in a nucleotide-dependent manner, and we mapped the protein–protein interaction interface. Finally, using guanosine triphosphate (GTP) hydrolysis assays, we demonstrate that BfNFeoAB exhibits one of the slowest known rates of Feo-mediated GTP hydrolysis that is not potassium-stimulated. Importantly, truncation of FeoA from this fusion demonstrates that FeoA–NFeoB interactions function to stabilize the GTP-bound form of FeoB. Taken together, our work reveals a role for FeoA function in the fused FeoAB system and suggests a function for FeoA among prokaryotes.

Iron oxide thin films grown on (00l) sapphire substrate by pulsed-laser deposition

Magnetite (Fe3O4) and wustite (FeO) are well-known oxides for their promising magnetic properties. However, growing stable FeOx thin films with controlled iron oxidation states could be of interest for further applications. In this work, we highlight the formation of different FeOx-based thin films grown by pulsed-laser deposition (PLD) from Fe or α-Fe2O3 targets onto sapphire substrates. Based on X-ray diffraction and Rutherford backscattering spectroscopy analyses, we report on films with various O/Fe ratios obtained by controlling both the substrate temperature and the oxygen pressure in the 10−5 – 10 Pa range during the PLD growth. Thus, the different crystalline phases of the Fe-O system can be grown: metallic iron, α-Fe2O3, Fe3O4, and the thermodynamically metastable phase FeO. On one hand, we demonstrate that at low pressures (< 10−4 Pa) metal-oxide composite thin films with both metallic Fe and Fe3O4 phase are epitaxially grown on the sapphire substrates even at room temperature. On the other hand, we highlight that using a α-Fe2O3 target, films composed with a mixture of wustite and spinel phases have been obtained at room temperature. The precise growth conditions leading to the formation of FeO-based films or metal-oxide composite films are discussed.

PERICLASE-SPINEL REFRACTORY MODIFIED ТІО2

Over the past decades, the development and improvement of refractory materials for lining high-temperature zones of rotary kilns continues. The main requirements for refractory products for lining rotary kilns for cement clinker roasting are: high density and ultimate compressive strength, low porosity and gas permeability, increased abrasion resistance, low thermal conductivity, high corrosion resistance and the ability to form a protective layer.Today, the main goal of modern researchers is to create a heat-resistant refractory with a flexible structure that ensures its integrity at high temperatures and mechanical loads, which have the ability to form a protective coating layer. In this work, a technological approach has been tested for introducing a vibro-milled modifier (briquette based on a high-alumina component and a titanium-containing additive) into the composition of the raw charge for periclase-spinel refractory in the form of a pre-synthesized product containing crystalline phases of the Al2O3 – TiO2 – FeO system. The basis for the production of periclase-spinel refractories modified with TiO2 is the four-component system MgO – Al2O3 – FeO – TiO2, on the basis of thermodynamic calculations of which the content of individual components of the charge was selected and the operational characteristics were predicted. The interrelation of physical and mechanical properties with the content of individual components in the initial charge warehouses is shown, and the directions of solid-phase processes with their participation are noted. The features of the microstructure of the sample material are noted in relation to the formation of an optimal set of properties. It is shown that the nature of the organization of micropores is favorable for increasing the thermal stability of the material, which complements the phase adaptation mechanism also with the structural effect of damping mechanical stresses during thermal cycling.