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      Elongated magnetite nanoparticle formation from a solid ferrous precursor in a magnetotactic bacterium

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          Abstract

          Magnetotactic bacteria are aquatic microorganisms that intracellularly mineralize ferrimagnetic nanoparticles enabling the cells to align with the geomagnetic field. The bacteria produce a magnetic mineral of species-specific phase (magnetite Fe(II)Fe(III) 2O 4 or greigite Fe(II)Fe(III) 2S 4), size, morphology and particle assembly. Several species produce crystals of unusual elongated particle shapes, which break the symmetry of the thermodynamically favoured isometric morphology. Such morphologies are thought to affect domain size and orientation of the internal magnetization. Therefore, they are interesting study objects to develop new synthetic strategies for the morphological control of nanoparticles. We investigate the formation of such irregularly shaped nanomagnets in the species Desulfovibrio magneticus RS-1. In contrast to previously described organisms, this bacterium accumulates iron predominantly as Fe(II) rather than Fe(III) consistent with an alternative oxidative biomineralization route. Further, using high-resolution electron microscopy, we observe an epitaxial relationship between precursor and the final mineral phase supporting the notion of a solid-state transformation pathway. The precursor is likely a green rust previously thought to convert to magnetite only by dissolution and re-precipitation. Our findings represent a novel observation in the interconversion of iron (oxyhydr)oxide materials and suggest that solid-state growth processes could be required to produce irregularly shaped, elongated magnetite nanocrystals.

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          Most cited references12

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          Aggregation-based crystal growth and microstructure development in natural iron oxyhydroxide biomineralization products.

          Crystals are generally considered to grow by attachment of ions to inorganic surfaces or organic templates. High-resolution transmission electron microscopy of biomineralization products of iron-oxidizing bacteria revealed an alternative coarsening mechanism in which adjacent 2- to 3-nanometer particles aggregate and rotate so their structures adopt parallel orientations in three dimensions. Crystal growth is accomplished by eliminating water molecules at interfaces and forming iron-oxygen bonds. Self-assembly occurs at multiple sites, leading to a coarser, polycrystalline material. Point defects (from surface-adsorbed impurities), dislocations, and slabs of structurally distinct material are created as a consequence of this growth mechanism and can dramatically impact subsequent reactivity.
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            Magnetotactic bacteria.

            Bacteria with motility directed by the local geomagnetic field have been observed in marine sediments. These magnetotactic microorganisms possess flagella and contain novel structured particles, rich in iron, within intracytoplasmic membrane vesicles. Conceivably these particles impart to cells a magnetic moment. This could explain the observed migration of these organisms in fields as weak as 0.5 gauss.
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              Magnetotactic bacteria and magnetosomes.

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                Author and article information

                Journal
                J R Soc Interface
                J R Soc Interface
                RSIF
                royinterface
                Journal of the Royal Society Interface
                The Royal Society
                1742-5689
                1742-5662
                November 2016
                November 2016
                : 13
                : 124
                : 20160665
                Affiliations
                [1 ]Department of Biomaterials, Max Planck Institute of Colloids and Interfaces , 14424 Potsdam, Germany
                [2 ]Institut de Minéralogie et de Physique des Milieux Condensés, Unité Mixte de Recherche 7590 Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, Institut de Recherches pour le Développement , Campus Jussieu, 75005 Paris, France
                Author notes

                Electronic supplementary material is available online at https://dx.doi.org/10.6084/m9.figshare.c.3571029.

                Author information
                http://orcid.org/0000-0002-5512-3249
                Article
                rsif20160665
                10.1098/rsif.2016.0665
                5134017
                27881802
                89ab69ac-735c-48f8-93d5-0b9975774447
                © 2016 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                History
                : 19 August 2016
                : 27 October 2016
                Funding
                Funded by: European Research Council, http://dx.doi.org/10.13039/501100000781;
                Award ID: 256915-MB2
                Categories
                1004
                15
                19
                23
                Life Sciences–Chemistry interface
                Research Article
                Custom metadata
                November, 2016

                Life sciences
                magnetite,magnetotactic bacteria,ferrous iron,biomineralization,precursor
                Life sciences
                magnetite, magnetotactic bacteria, ferrous iron, biomineralization, precursor

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