title: Crystal growth of bullet-shaped magnetite in magnetotactic bacteria of the Nitrospirae phylum.
abstract: Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along the Earth's magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomineralization. Moreover, the determination of their specific crystallographic signature (e.g. structure and morphology) is essential for palaeoenvironmental and ancient-life studies. Yet, the mechanisms of MTB biomineralization remain poorly understood, although this process has been extensively studied in several cultured MTB strains in the Proteobacteria phylum. Here, we show a comprehensive transmission electron microscopy (TEM) study of magnetic and structural properties down to atomic scales on bullet-shaped magnetites produced by the uncultured strain MYR-1 belonging to the Nitrospirae phylum, a deeply branching phylogenetic MTB group. We observed a multiple-step crystal growth of MYR-1 magnetite: initial isotropic growth forming cubo-octahedral particles (less than approx. 40 nm), subsequent anisotropic growth and a systematic final elongation along [001] direction. During the crystal growth, one major {111} face is well developed and preserved at the larger basal end of the crystal. The basal {111} face appears to be terminated by a tetrahedral-octahedral-mixed iron surface, suggesting dimensional advantages for binding protein(s), which may template the crystallization of magnetite. This study offers new insights for understanding magnetite biomineralization within the Nitrospirae phylum.
authors.affiliation: Paleomagnetism and Geochronology Lab, Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, People's Republic of China Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités-UPMC Univ Paris 06, UMR CNRS 7590, Muséum National d'Histoire Naturelle (MNHN), IRD UMR 206, 4 Place Jussieu, Paris 75005, France France-China Biomineralization and Nano-structures Laboratory, Chinese Academy of Sciences, Beijing 100029, People's Republic of China lijinhua@mail.iggcas.ac.cn.
authors.forename: Jinhua
authors.initials: J
authors.lastname: Li
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités-UPMC Univ Paris 06, UMR CNRS 7590, Muséum National d'Histoire Naturelle (MNHN), IRD UMR 206, 4 Place Jussieu, Paris 75005, France nicolas.menguy@upmc.fr.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Menguy
authors.affiliation: CEMES/CNRS; BP 94347, Toulouse Cedex 31055, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Gatel
authors.affiliation: CEMES/CNRS; BP 94347, Toulouse Cedex 31055, France.
authors.forename: Victor
authors.initials: V
authors.lastname: Boureau
authors.affiliation: CEMES/CNRS; BP 94347, Toulouse Cedex 31055, France.
authors.forename: Etienne
authors.initials: E
authors.lastname: Snoeck
authors.affiliation: LPN-UPR20/CNRS, Route de Nozay, Marcoussis 91460, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Patriarche
authors.affiliation: France Chimie Métallurgique des Terres Rares, ICMPE, UMR 7182, CNRS, 2-8 rue Henri Dunant, Thiais Cedex 94320, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Leroy
authors.affiliation: Paleomagnetism and Geochronology Lab, Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, People's Republic of China France-China Biomineralization and Nano-structures Laboratory, Chinese Academy of Sciences, Beijing 100029, People's Republic of China yxpan@mail.iggcas.ac.cn.
authors.forename: Yongxin
authors.initials: Y
authors.lastname: Pan
mesh_terms: D003460:Crystallization; D055032:Electron Microscope Tomography; D052203:Ferrosoferric Oxide / Q000378:metabolism*; D020560:Proteobacteria / Q000378:metabolism* / Q000648:ultrastructure*
chemical_list: D052203:Ferrosoferric Oxide
keywords: Nitrospirae phylum; biomineralization; bullet-shaped magnetite; crystal growth; magnetotactic bacteria; micromagnetic property