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 cor

A Milestone in the Chemical Synthesis of Fe3O4 Nanoparticles Unreported Bulklike Properties Lead to a Remarkable Magnetic Hyperthermia

Among iron oxide phases, magnetite Fe3O4 is often the preferred one for nanotechnological and biomedical applications because of its high saturation magnetization and low toxicity. Although there are several synthetic routes that attempt to reach magnetite nanoparticles NPs , they are usually referred as IONPs iron oxide NPs due to the great difficulty in obtaining the monophasic and stoichiometric Fe3O4 phase. Added to this problem is the common increase of size shape polydispersity when larger NPs D gt; 20 nm are synthesized. An unequivocal correlation between a nanomaterial and its properties can only be achieved by the production of highly homogeneous systems, which, in turn, is only possible by the continuous improvement of synthesis methods. There is no doubt that solving the compositional heterogeneity of IONPs while keeping them monodisperse remains a challenge for synthetic chemistry. Herein, we present a methodical optimization of the iron oleate decomposition method to obtain Fe3O4 single nanocrystals without any trace of secondary phases and with no need of postsynthetic treatment. The average dimension of the NPs, ranging from 20 to 40 nm, has been tailored by adjusting the total volume and the boiling point of the reaction mixture. Mössbauer spectroscopy and DC magnetometry have revealed that the NPs present a perfectly stoichiometric Fe3O4 phase. The high saturation magnetization 93 2 A m2 kg at RT and the extremely sharp Verwey transition at around 120 K shown by these NPs have no precedent. Moreover, the synthesis method has been refined to obtain NPs with octahedral morphology and suitable magnetic anisotropy, which significantly improves the magnetic hyperthemia performance. The heating power of properly PEGylated nano octahedrons has been investigated by AC magnetometry, confirming that the NPs present negligible dipolar interactions, which leads to an outstanding magnetothermal efficiency that does not change when the NPs are dispersed in environments with high viscosity and ionic strength. Additionally, the heat production of the NPs within physiological media has been directly measured by calorimetry under clinically safe conditions, reasserting the excellent adequacy of the system for hyperthermia therapies. To the best of our knowledge, this is the first time that such bulklike magnetite NPs with minimal size shape polydispersity, minor agglomeration, and exceptional heating power are chemically synthesize

Elucidating the role of shape anisotropy in faceted magnetic nanoparticles using biogenic magnetosomes as a model

Shape anisotropy is of primary importance to understand the magnetic behavior of nanoparticles, but a rigorous analysis in polyhedral morphologies is missing. In this work, a model based on finite element techniques has been developed to calculate the shape anisotropy energy landscape for cubic, octahedral, and truncated octahedral morphologies. In all cases, a cubic shape anisotropy is found that evolves to quasi uniaxial anisotropy when the nanoparticle is elongated amp; 8805;2 . This model is tested on magnetosomes, amp; 8764;45 nm truncated octahedral magnetite nanoparticles forming a chain inside Magnetospirillum gryphiswaldense MSR 1 bacteria. This chain presents a slightly bent helical configuration due to a 20 tilting of the magnetic moment of each magnetosome out of chain axis. Electron cryotomography images reveal that these magnetosomes are not ideal truncated octahedrons but present amp; 8776;7.5 extrusion of one of the 001 square faces and amp; 8776;10 extrusion of an adjacent 111 hexagonal face. Our model shows that this deformation gives rise to a quasi uniaxial shape anisotropy, a result of the combination of a uniaxial Ksh u 7 kJ m amp; 8722;3 and a cubic Ksh c 1.5 kJ m amp; 8722;3 contribution, which is responsible for the 20 tilting of the magnetic moment. Finally, our results have allowed us to accurately reproduce, within the framework of the Landau Lifshitz Gilbert model, the experimental AC loops measured for these magnetotactic bacteri

Tuning the Magnetic Response of Magnetospirillum magneticum by Changing the Culture Medium A Straightforward Approach to Improve Their Hyperthermia Efficiency

Magnetotactic bacteria Magnetospirillum magneticum AMB 1 have been cultured using three different media magnetic spirillum growth medium with Wolfe s mineral solution MSGM W , magnetic spirillum growth medium without Wolfe s mineral solution MSGM W , and flask standard medium FSM . The influence of the culture medium on the structural, morphological, and magnetic characteristics of the magnetosome chains biosynthesized by these bacteria has been investigated by using transmission electron microscopy, X ray absorption spectroscopy, and X ray magnetic circular dichroism. All bacteria exhibit similar average size for magnetosomes, 40 45 nm, but FSM bacteria present slightly longer subchains. In MSGM W bacteria, Co2 ions present in the medium substitute Fe2 ions in octahedral positions with a total Co doping around 4 5 . In addition, the magnetic response of these bacteria has been thoroughly studied as functions of both the temperature and the applied magnetic field. While MSGM W and FSM bacteria exhibit similar magnetic behavior, in the case of MSGM W, the incorporation of the Co ions affects the magnetic response, in particular suppressing the Verwey amp; 8764;105 K and low temperature amp; 8764;40 K transitions and increasing the coercivity and remanence. Moreover, simulations based on a Stoner Wolhfarth model have allowed us to reproduce the experimentally obtained magnetization versus magnetic field loops, revealing clear changes in different anisotropy contributions for these bacteria depending on the employed culture medium. Finally, we have related how these magnetic changes affect their heating efficiency by using AC magnetometric measurements. The obtained AC hysteresis loops, measured with an AC magnetic field amplitude of up to 90 mT and a frequency, f, of 149 kHz, reveal the influence of the culture medium on the heating properties of these bacteria below 35 mT, MSGM W bacteria are the best heating mediators, but above 60 mT, FSM and MSGM W bacteria give the best heating results, reaching a maximum heating efficiency or specific absorption rate SAR of SAR f amp; 8776; 12 W g 1 kHz

Shaping Up Zn Doped Magnetite Nanoparticles from Mono and Bimetallic Oleates The Impact of Zn Content, Fe Vacancies, and Morphology on Magnetic Hyperthermia Performance

The currently existing magnetic hyperthermia treatments usually need to employ very large doses of magnetic nanoparticles MNPs and or excessively high excitation conditions H f gt; 1010 A m s to reach the therapeutic temperature range that triggers cancer cell death. To make this anticancer therapy truly minimally invasive, it is crucial the development of improved chemical routes that give rise to monodisperse MNPs with high saturation magnetization and negligible dipolar interactions. Herein, we present an innovative chemical route to synthesize Zn doped magnetite NPs based on the thermolysis of two kinds of organometallic precursors i a mixture of two monometallic oleates FeOl ZnOl , and ii a bimetallic ironzinc oleate Fe3 amp; 8722;yZnyOl . These approaches have allowed tailoring the size 10 amp; 8722;50 nm , morphology spherical, cubic, and cuboctahedral , and zinc content ZnxFe3 amp; 8722;xO4, 0.05 lt; x lt; 0.25 of MNPs with high saturation magnetization amp; 8805;90 Am2 kg at RT . The oxidation state and the local symmetry of Zn2 and Fe2 3 cations have been investigated by means of X ray absorption near edge structure XANES spectroscopy, while the Fe center distribution and vacancies within the ferrite lattice have been examined in detail through Mo amp; 776;ssbauer spectroscopy, which has led to an accurate determination of the stoichiometry in each sample. To achieve good biocompatibility and colloidal stability in physiological conditions, the ZnxFe3 amp; 8722;xO4 NPs have been coated with high molecular weight poly ethylene glycol PEG . The magnetothermal efficiency of ZnxFe3 amp; 8722;xO4 PEG samples has been systematically analyzed in terms of composition, size, and morphology, making use of the latest generation AC magnetometer that is able to reach 90 mT. The heating capacity of Zn0.06Fe2.94O4 cuboctahedrons of 25 nm reaches a maximum value of 3652 W g at 40 kA m and 605 kHz , but most importantly, they reach a highly satisfactory value 600 W g under strict safety excitation conditions at 36 kA m and 125 kHz . Additionally, the excellent heating power of the system is kept identical both immobilized in agar and in the cellular environment, proving the great potential and reliability of this platform for magnetic hyperthermia therapie

Incorporation of Tb and Gd improves the diagnostic functionality of magnetotactic bacteria

Magnetotactic bacteria are envisaged as potential theranostic agents. Their internal magnetic compass, chemical environment specificity and natural motility enable these microorganisms to behave as nanorobots, as they can be tracked and guided towards specific regions in the body and activated to generate a therapeutic response. Here we provide additional diagnostic functionalities to magnetotactic bacteria Magnetospirillum gryphiswaldense MSR 1 while retaining their intrinsic capabilities. These additional functionalities are achieved by incorporating Tb or Gd in the bacteria by culturing them in Tb Gd supplemented media. The incorporation of Tb provides luminescence properties, enabling potential applications of bacteria as biomarkers. The incorporation of Gd turns bacteria into dual contrast agents for magnetic resonance imaging, since Gd adds T1 contrast to the existing T2 contrast of unmodified bacteria. Given their potential clinical applications, the diagnostic ability of the modified MSR 1 has been successfully tested in vitro in two cell models, confirming their suitability as fluorescent markers Tb MSR 1 and dual contrast agents for MRI Gd MSR

Influence of the Structure in Magnetic Properties in Co-P Electrodeposited Amorphous Alloys

The short range order of a series of Co100-xPx (17<x<26) amorphous alloys prepared by electrodeposition is studied by EXAFS. The structural parameters as coordination numbers and interatomic distances have been found to vary significantly with P concentration. This behaviour contrasts with that of Fe-P alloys where the environment of the Fe atoms does not change appreciably with composition. The structural differences between both systems are related with clear differences in the magnetic properties, most of all in the dependence on concentration of the Curie temperature

EXAFS and Mössbauer Study of the Crystallization of Fe91Zr9 Metallic Glass

The crystallization process of the Fe91Zr9 amorphous alloy has been followed by means of two experimental techniques, EXAFS and Mössbauer spectroscopy. X-ray absorption spectra on Fe K-edge and Mössbauer spectra of six samples with different degrees of crystallization have been measured at room temperature in order to obtain information about the structural changes that take place. From the beginning of the crystallization process it is clearly seen that a crystalline phase with a bcc-type structure appears. From the obtained data we can conclude that this phase is nearly pure bcc-Fe, with small amount of impurities in its structure

Observation of a Strong Short Range Order in Co Rich Amorphous Alloys Prepared by Different Methods

X-ray absorption spectroscopy has been used to compare the short range order of some Fe-Co based amorphous alloys with low Fe concentration prepared by different methods : melt spinning (samples of FeCoSiB) and electrodeposition (FeCoP). Both the EXAFS and XANES analysis indicates that the chemical affinity of the metalloids Si or P for the Co atoms underlies the strong increase of the topological short range order around the Fe atoms. This ordering enhancement involves several coordination shells above the first one and results to be independent of the sample preparation procedure as well as the nature of the metalloids (Si or P). The large differences observed between the local structure around the Fe and Co atoms strongly suggest the existence of an inhomogeneous distribution of Fe, or Fe-B, in the bulk amorphous structure of the Co rich alloys, which takes places when the Si or P concentration is higher than the Fe one