Modifying the magnetic response of magnetotactic bacteria: incorporation of Gd and Tb ions into the magnetosome structure.

Magnetotactic bacteria Magnetospirillum gryphiswaldense MSR-1 biosynthesise chains of cube-octahedral magnetosomes, which are 40 nm magnetite high quality (Fe3O4) nanoparticles. The magnetic properties of these crystalline magnetite nanoparticles, which can be modified by the addition of other elements into the magnetosome structure (doping), are of prime interest in a plethora of applications, those related to cancer therapy being some of the most promising ones. Although previous studies have focused on transition metal elements, rare earth (RE) elements are very interesting as doping agents, both from a fundamental point of view (e.g. significant differences in ionic sizes) and for the potential applications, especially in biomedicine (e.g. magnetic resonance imaging and luminescence). In this work, we have investigated the impact of Gd and Tb on the magnetic properties of magnetosomes by using different complementary techniques. X-ray diffraction, transmission electron microscopy, and X-ray absorption near edge spectroscopy analyses have revealed that a small amount of RE ions, ∼3-4%, incorporate into the Fe3O4 structure as Gd3+ and Tb3+ ions. The experimental magnetic characterisation has shown a clear Verwey transition for the RE-doped bacteria, located at T ∼ 100 K, which is slightly below the one corresponding to the undoped ones (106 K). However, we report a decrease in the coercivity and remanence of the RE-doped bacteria. Simulations based on the Stoner-Wohlfarth model have allowed us to associate these changes in the magnetic response with a reduction of the magnetocrystalline (K C) and, especially, the uniaxial (K uni) anisotropies below the Verwey transition. In this way, K uni reaches a value of 23 and 26 kJ m-3 for the Gd- and Tb-doped bacteria, respectively, whilst a value of 37 kJ m-3 is obtained for the undoped bacteria.

Correction: Modifying the magnetic response of magnetotactic bacteria: incorporation of Gd and Tb ions into the magnetosome structure.

[This corrects the article DOI: 10.1039/D2NA00094F.].

Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet.

The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing.

Magnetosomes could be protective shields against metal stress in magnetotactic bacteria.

Magnetotactic bacteria are aquatic microorganisms with the ability to biomineralise membrane-enclosed magnetic nanoparticles, called magnetosomes. These magnetosomes are arranged into a chain that behaves as a magnetic compass, allowing the bacteria to align in and navigate along the Earth's magnetic field lines. According to the magneto-aerotactic hypothesis, the purpose of producing magnetosomes is to provide the bacteria with a more efficient movement within the stratified water column, in search of the optimal positions that satisfy their nutritional requirements. However, magnetosomes could have other physiological roles, as proposed in this work. Here we analyse the role of magnetosomes in the tolerance of Magnetospirillum gryphiswaldense MSR-1 to transition metals (Co, Mn, Ni, Zn, Cu). By exposing bacterial populations with and without magnetosomes to increasing concentrations of metals in the growth medium, we observe that the tolerance is significantly higher when bacteria have magnetosomes. The resistance mechanisms triggered in magnetosome-bearing bacteria under metal stress have been investigated by means of x-ray absorption near edge spectroscopy (XANES). XANES experiments were performed both on magnetosomes isolated from the bacteria and on the whole bacteria, aimed to assess whether bacteria use magnetosomes as metal storages, or whether they incorporate the excess metal in other cell compartments. Our findings reveal that the tolerance mechanisms are metal-specific: Mn, Zn and Cu are incorporated in both the magnetosomes and other cell compartments; Co is only incorporated in the magnetosomes, and Ni is incorporated in other cell compartments. In the case of Co, Zn and Mn, the metal is integrated in the magnetosome magnetite mineral core.

Configuration of the magnetosome chain: a natural magnetic nanoarchitecture.

Magnetospirillum gryphiswaldense is a microorganism with the ability to biomineralize magnetite nanoparticles, called magnetosomes, and arrange them into a chain that behaves like a magnetic compass. Rather than straight lines, magnetosome chains are slightly bent, as evidenced by electron cryotomography. Our experimental and theoretical results suggest that due to the competition between the magnetocrystalline and shape anisotropies, the effective magnetic moment of individual magnetosomes is tilted out of the [111] crystallographic easy axis of magnetite. This tilt does not affect the direction of the chain net magnetic moment, which remains along the [111] axis, but explains the arrangement of magnetosomes in helical-like shaped chains. Indeed, we demonstrate that the chain shape can be reproduced by considering an interplay between the magnetic dipolar interactions between magnetosomes, ruled by the orientation of the magnetosome magnetic moment, and a lipid/protein-based mechanism, modeled as an elastic recovery force exerted on the magnetosomes.

Influence of the bacterial growth phase on the magnetic properties of magnetosomes synthesized by Magnetospirillum gryphiswaldense.

BACKGROUND: The magnetosome biosynthesis is a genetically controlled process but the physical properties of the magnetosomes can be slightly tuned by modifying the bacterial growth conditions. METHODS: We designed two time-resolved experiments in which iron-starved bacteria at the mid-logarithmic phase are transferred to Fe-supplemented medium to induce the magnetosomes biogenesis along the exponential growth or at the stationary phase. We used flow cytometry to determine the cell concentration, transmission electron microscopy to image the magnetosomes, DC and AC magnetometry methods for the magnetic characterization, and X-ray absorption spectroscopy to analyze the magnetosome structure. RESULTS: When the magnetosomes synthesis occurs during the exponential growth phase, they reach larger sizes and higher monodispersity, displaying a stoichiometric magnetite structure, as fingerprinted by the well defined Verwey temperature. On the contrary, the magnetosomes synthesized at the stationary phase reach smaller sizes and display a smeared Verwey transition, that suggests that these magnetosomes may deviate slightly from the perfect stoichiometry. CONCLUSIONS: Magnetosomes magnetically closer to stoichiometric magnetite are obtained when bacteria start synthesizing them at the exponential growth phase rather than at the stationary phase. GENERAL SIGNIFICANCE: The growth conditions influence the final properties of the biosynthesized magnetosomes. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editors: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

Studying nanoparticles' 3D shape by aspect maps: Determination of the morphology of bacterial magnetic nanoparticles.

Magnetic nanoparticles (MNPs) are widely investigated due to their potential use in various applications, ranging from electronics to biomedical devices. The magnetic properties of MNPs are strongly dependent on their size and shape (i.e., morphology), thus appropriate tools to investigate their morphology are fundamental to understand the physics of these systems. Recently a new approach to study nanoparticle morphology by Transmission Electron Microscopy (TEM) analysis has been proposed, introducing the so-called Aspect Maps (AMs). In this paper, a further evolution of the AM method is presented, allowing determination of the nanoparticles' 3D shape by TEM image. As a case study, this paper will focus on magnetite nanoparticles (Fe3O4), with a mean size of ∼45 nm extracted from Magnetospirillum gryphiswaldense magnetostatic bacteria (MTB). The proposed approach gives a complete description of the nanoparticles' morphology, allowing estimation of an average geometrical size and shape. In addition, preliminary investigation of the magnetic properties of MTB nanoparticles was performed, giving some insight into interparticle interactions and on the reversal mechanism of the magnetization.

On the mineral core of ferritin-like proteins: structural and magnetic characterization.

It is generally accepted that the mineral core synthesized by ferritin-like proteins consists of a ferric oxy-hydroxide mineral similar to ferrihydrite in the case of horse spleen ferritin (HoSF) and an oxy-hydroxide-phosphate phase in plant and prokaryotic ferritins. The structure reflects a dynamic process of deposition and dissolution, influenced by different biological, chemical and physical variables. In this work we shed light on this matter by combining a structural (High Resolution Transmission Electron Microscopy (HRTEM) and Fe K-edge X-ray Absorption Spectroscopy (XAS)) and a magnetic study of the mineral core biomineralized by horse spleen ferritin (HoSF) and three prokaryotic ferritin-like proteins: bacterial ferritin (FtnA) and bacterioferritin (Bfr) from Escherichia coli and archaeal ferritin (PfFtn) from Pyrococcus furiosus. The prokaryotic ferritin-like proteins have been studied under native conditions and inside the cells for the sake of preserving their natural attributes. They share with HoSF a nanocrystalline structure rather than an amorphous one as has been frequently reported. However, the presence of phosphorus changes drastically the short-range order and magnetic response of the prokaryotic cores with respect to HoSF. The superparamagnetism observed in HoSF is absent in the prokaryotic proteins, which show a pure atomic-like paramagnetic behaviour attributed to phosphorus breaking the Fe-Fe exchange interaction.

Diente supernumerario retenido en posición invertida: reporte de un caso: revisión de literatura / Tooth supernumerary retained in upside: report of a case: review of literature

Los dientes supernumerarios representan una anomalía del desarrollo caracterizada por un excedente en la formula dental normal, su etiología no se encuentra claramente identificada, sin embargo, entre las reportadas, toma importancia la relacionada con alteraciones durante la fase de inicio y proliferación del desarrollo dental. Epidemiológicamente suele presentarse con mayor frecuencia en maxilar que en mandíbula, mas que hombres que en mujeres y con prevalencia en la dentición permanente. El diagnóstico se lleva acabo básicamente mediante radiografías, sin embargo el método clínico puede ser usado de acuerdo las condiciones bajo las cuales se presente. El tratamiento de elección es la excisión quirúrgica. A continuación se reporta un caso de paciente masculino, de 22 años de edad que asiste a consulta para la eliminación quirúrgica de diente supernumerario a nivel de la mandíbula en zona posteroinferior.

Supernumerary teeth are a development anomaly, characterised by over-abundance of teeth in the regular dental formula. The aetiology hasn't been clearly identified, however, among reported cases, alterations during the initial and proliferation phase of dental growth have been found. Epidemiologically, this anomaly appears more frequently in maxilla, male patients and permanent dentition. Diagnosis is carried out by means of radiographies and clinical examination. The treatment of choice is surgical removal. In the following case report, a 22 year- old- male patient who will have supernumerary teeth surgically removed of left posteroinferior mandibular area.

Micosis superficiales en adultos mayores residentes de la unidad geriátrica “Monseñor Dr. Rafael Arias Blanco” De Juan Griego Estado Nueva Esparta-Venezuela / Superficial mycoses in old people residents of the geriatrical unit “Monseñor Dr. Rafael Arias Blanco” Juan Griego Nueva Esparta state Venezuela

Se evaluó la frecuencia de micosis superficiales en una población de 71 adultos mayores entre 62 y 98 años, de sexo masculino y femenino, residentes de la Unidad Geriátrica, durante el periodo octubre 2005-Febrero 2006, de los cuales 49 presentaron diagnóstico sugestivo. A las muestras obtenidas, se les practicó examen directo con KOH al 10%, se cultivaron en agar Fungobiotic y se incubaron durante 15 días a temperatura ambiente. Las colonias filamentosas se identificaron a través de las características macro y microscópicas, mientras que las levaduras del género Candida por el sistema de identificación API 20 C AUX®. Los resultados obtenidos fueron analizados a través del método de análisis porcentual (%) y la prueba de Chi-cuadrado (c²). Resultaron positivos 40 (81,63%) casos, de los cuales el 82,50% fueron para candidosis cutáneas, siendo la candidosis ungueal la más frecuente, seguido de la tinea unguium (12,50%) y las onicomicosis por hongos no dermatofitos (5,00%). No se detectó ningún caso de pitiriasis versicolor. C. albicans fue el hongo más frecuentemente aislado (64,81%), sobre todo en uñas de pies, seguido de C. parapsilosis (12,96%) y Trichophyton mentagrophytes (5,56%). En la vejez, se observa una alta incidencia de candidosis cutáneas, la cual es favorecida por las condiciones físicas propias del adulto mayor, enfermedades concomitantes, déficit en la inmunidad celular y ciertos factores predisponentes como el ritmo de vida, el uso de calzados cerrados, el clima cálido y la humedad de la región donde se reside.

Determination of vanadium accumulation in onion root cells (Allium cepa L) and its correlation with toxicity

The vanadium is a metal that presents great interest from the toxicological point of view, because of the numerous alterations that can take place in different biological systems. This work evaluated the capacity of vanadium accumulation and its correlation with genotoxic effects in root cells of Allium cepa L. The bulbs were cultivated in renovated filtered water each 24 h, at a temperature of 25 +/- 0.5 degrees C, in darkness and constant aeration. Treatments were carried out under the same experimental conditions, using water solutions of vanadium of 25, 50, 75 and 100 microg/g for 0, 12, 24, 48 and 72 h. A control was carried out where metal solution was substituted by distilled water. After the treatment, the meristems were fixed with alcohol--acetic acid (3:1) and stained according to the technique of Feulge n. The capacity of accumulation was determined by GFAAS. The analysis of the results revealed an accumulation of the metal for all times and concentrations. No correlation was presented among vanadium accumulation, growth and mitotic index; however, positive correlation was given with the induction of chromosomic aberrations. In conclusion, vanadium is able to induce cytotoxic effect in the exposed roots, but only genotoxic effect was correlated with metal accumulation.

Determination of vanadium accumulation in onion root cells (Allium cepa L) and its correlation with toxicity

The vanadium is a metal that presents great interest from the toxicological point of view, because of the numerous alterations that can take place in different biological systems. This work evaluated the capacity of vanadium accumulation and its correlation with genotoxic effects in root cells of Allium cepa L. The bulbs were cultivated in renovated filtered water each 24 h, at a temperature of 25 +/- 0.5 degrees C, in darkness and constant aeration. Treatments were carried out under the same experimental conditions, using water solutions of vanadium of 25, 50, 75 and 100 microg/g for 0, 12, 24, 48 and 72 h. A control was carried out where metal solution was substituted by distilled water. After the treatment, the meristems were fixed with alcohol--acetic acid (3:1) and stained according to the technique of Feulge n. The capacity of accumulation was determined by GFAAS. The analysis of the results revealed an accumulation of the metal for all times and concentrations. No correlation was presented among vanadium accumulation, growth and mitotic index; however, positive correlation was given with the induction of chromosomic aberrations. In conclusion, vanadium is able to induce cytotoxic effect in the exposed roots, but only genotoxic effect was correlated with metal accumulation.(AU)

DNA injury induced by 5-aminouracil and caffeine in G2 checkpoints path of higher plant cells.

This work evaluated the qualitative and quantitative cellular changes induced by treatment with 5-aminouracil (5-AU) and a combination of 5-AU and caffeine in plant cells in relation to DNA damage, repaired damage, and residual damage. As biological material, Allium cepa L. root tips were used, grown in filtered water, in darkness, with aeration at constant temperature of 25 degrees C +/- 0.5. Cell populations were synchronized using 5 mM caffeine in order to study the effects of 5-AU and caffeine/5-AU combined treatment on the DNA content and their incidence in the entrance to mitosis. The results showed a delay in the G2 period due to induced DNA damage by the 5-AU and caffeine/5-AU combined treatment, shown by aberrant metaphases, anaphases and telophases. The effect of caffeine in the combined treatment was heightened in spite of lengthening the checkpoints route that retains the cells in G2. The existence of G2 checkpoints was shown in the cell population studied, inducing lesions in the DNA, chromosomic aberrations and cellular instability.

DNA injury induced by 5-aminouracil and caffeine in G2 checkpoints path of higher plant cells

This work evaluated the qualitative and quantitative cellular changes induced by treatment with 5-aminouracil (5-AU) and a combination of 5-AU and caffeine in plant cells in relation to DNA damage, repaired damage, and residual damage. As biological material, Allium cepa L. root tips were used, grown in filtered water, in darkness, with aeration at constant temperature of 25°C ± 0.5. Cell populations were synchronized using 5 mM caffeine in order to study the effects of 5-AU and caffeine/5-AU combined treatment on the DNA content and their incidence in the entrance to mitosis. The results showed a delay in the G2 period due to induced DNA damage by the 5-AU and caffeine/5-AU combined treatment, shown by aberrant metaphases, anaphases and telophases. The effect of caffeine in the combined treatment was heightened in spite of lengthening the checkpoints route that retains the cells in G2. The existence of G2 checkpoints was shown in the cell population studied, inducing lesions in the DNA, chromosomic aberrations and cellular instability

DNA injury induced by 5-aminouracil and caffeine in G2 checkpoints path of higher plant cells

This work evaluated the qualitative and quantitative cellular changes induced by treatment with 5-aminouracil (5-AU) and a combination of 5-AU and caffeine in plant cells in relation to DNA damage, repaired damage, and residual damage. As biological material, Allium cepa L. root tips were used, grown in filtered water, in darkness, with aeration at constant temperature of 25ºC ± 0.5. Cell populations were synchronized using 5 mM caffeine in order to study the effects of 5-AU and caffeine/5-AU combined treatment on the DNA content and their incidence in the entrance to mitosis. The results showed a delay in the G2 period due t

DNA injury induced by 5-aminouracil and caffeine in G2 checkpoints path of higher plant cells.

This work evaluated the qualitative and quantitative cellular changes induced by treatment with 5-aminouracil (5-AU) and a combination of 5-AU and caffeine in plant cells in relation to DNA damage, repaired damage, and residual damage. As biological material, Allium cepa L. root tips were used, grown in filtered water, in darkness, with aeration at constant temperature of 25 degrees C +/- 0.5. Cell populations were synchronized using 5 mM caffeine in order to study the effects of 5-AU and caffeine/5-AU combined treatment on the DNA content and their incidence in the entrance to mitosis. The results showed a delay in the G2 period due to induced DNA damage by the 5-AU and caffeine/5-AU combined treatment, shown by aberrant metaphases, anaphases and telophases. The effect of caffeine in the combined treatment was heightened in spite of lengthening the checkpoints route that retains the cells in G2. The existence of G2 checkpoints was shown in the cell population studied, inducing lesions in the DNA, chromosomic aberrations and cellular instability.

Cytotoxicity and mode of action of maleic hydrazide in root tips of Allium cepa L.

Maleic hydrazide (MH) is an herbicide and is a regulator of the growth of buds in vegetables during storage. It is used in agriculture-in despite its known effect as a mutagenic and clastogenic agent. In this research the effect of MH on the root tips of Allium cepa L. was determined; correlations between the effects of different concentrations and exposure times on the mitotic index (MI) and induction of chromosomal aberrations (ChA) were also examined. Experiments were carried out in triplicate, using aqueous solutions of MH to concentrations of 10(-6), 10(-5), 10(-4) and 10(-3)M, at intervals of 0, 4, 8, 12, 24, and 48 h, with a control for each combination (with the MH substituted by distilled water). The results revealed an inhibition of the MI linked to the concentration and time of treatment (F=845.51, P<0.01 and F=427.58, P<0.01, respectively). For all the concentrations used and exposure periods longer than 12 h, different types of ChA were present, with significantly increased frequencies with increases in the concentration and time of exposure (P<0.01). To determine the mechanism through which the herbicide exerts its toxicity, ultrastructural electron microscopy was conducted. The results reveal nucleolar alterations, suggesting an inhibitory effect of biosynthetic activity.

Inflammation induced increase of fluoride resistant acid phosphatase (FRAP) activity in the spinal dorsal horn in rats.

Fluoride-resistant acid phosphatase (FRAP) has been suggested as an enzymatic marker for nociceptive primary afferent terminals in the spinal dorsal horn, however there has not been demonstrated a direct functional relation between FRAP activity and an increased nociceptive transmission. For this purpose, we quantitated FRAP activity in the spinal dorsal horn of the rat in a heat-induced cutaneous inflammatory model. Male Sprague-Dawley rats anaesthetised with thiopental were separated in two groups where the left hindpaw was submerged during 60 s either in water at room temperature (control group) or in water at 60 degrees C (inflammation group) which induce in this group a progressive hindpaw inflammation. After 8 h, the lumbar enlargement of the spinal cord was extracted, cut in slices and 1 mm micropunch fragments were obtained from the right and left dorsal horn. The activity of FRAP was determined using the Gomori colorimetric method and corrected by the protein concentrations. FRAP activity in the left dorsal horn was statistically higher than right dorsal horn in the inflammation group (3.05+/-0.54 versus 1.91+/-0.23 u/g per l; P<0.05). Also, FRAP activity from the left dorsal horn of the control and inflammation groups show a significant increase in the last group (3.05+/-0.54 versus 2.17+/-0.23 u/g per l; P<0.05). This results demonstrate that FRAP is not only an enzymatic marker for neuronal and fibre integrity of nociceptive primary afferents but also it is associated to the nociceptive afferent activation.

Effect of cadmium on the nucleoli of meristematic cells of onion Allium cepa L: an ultrastructural study.

This study of the effect of cadmium on nucleolar ultrastructure was carried out with meristematic cell populations of Allium cepa L. Meristems, grown at 25 degrees C, were treated with 10 ppm cadmium chloride. Conventional and silver staining techniques were carried out, and the ultrastructure was analyzed using electron microscopy. Observation showed alterations in the nucleoli of the cells that had been treated with cadmium and this effect varied according to the time of exposure to the metal. After 4h of treatment, nucleolar segregation was observed in interphase, probably because of the effect of cadmium on the synthesis of ribosomal RNA precursors. A decrease in the fibrillar to granular component ratio also occurred in the cells exposed to Cd2+ for 8 h. Some changes were observed in the G1 cells; their chromatin still remained very condensed, and prenucleolus bodies remained scattered within the nucleus. At the same time, there was a large amount of interchromatin granules. These changes produced by cadmium resembled those produced during inhibition of RNA synthesis. The fibrillar bodies, another morphologic feature, resulting from a blocked transcription, were also evidenced. All these observations suggest that one of the ways that cadmium exercises its toxicity is by altering the biosynthesis of the preribosomal RNA precursor.