title: Anisotropy of bullet-shaped magnetite nanoparticles in the magnetotactic bacteria Desulfovibrio magneticus sp. Strain RS-1.
abstract: Magnetotactic bacteria (MTB) build magnetic nanoparticles in chain configuration to generate a permanent dipole in their cells as a tool to sense the Earth's magnetic field for navigation toward favorable habitats. The majority of known MTB align their nanoparticles along the magnetic easy axes so that the directions of the uniaxial symmetry and of the magnetocrystalline anisotropy coincide. Desulfovibrio magneticus sp. strain RS-1 forms bullet-shaped magnetite nanoparticles aligned along their (100) magnetocrystalline hard axis, a configuration energetically unfavorable for formation of strong dipoles. We used ferromagnetic resonance spectroscopy to quantitatively determine the magnetocrystalline and uniaxial anisotropy fields of the magnetic assemblies as indicators for a cellular dipole with stable direction in strain RS-1. Experimental and simulated ferromagnetic resonance spectral data indicate that the negative effect of the configuration is balanced by the bullet-shaped morphology of the nanoparticles, which generates a pronounced uniaxial anisotropy field in each magnetosome. The quantitative comparison with anisotropy fields of Magnetospirillum gryphiswaldense, a model MTB with equidimensional magnetite particles aligned along their (111) magnetic easy axes in well-organized chain assemblies, shows that the effectiveness of the dipole is similar to that in RS-1. From a physical perspective, this could be a reason for the persistency of bullet-shaped magnetosomes during the evolutionary development of magnetotaxis in MTB.
authors.affiliation: Department of Physics, University of California, Berkeley, California.
authors.forename: Michalis
authors.initials: M
authors.lastname: Chariaou
authors.affiliation: Plant and Microbial Biology, University of California, Berkeley, California.
authors.forename: Lilah
authors.initials: L
authors.lastname: Rahn-Lee
authors.affiliation: Institute of Geophysics, ETH Zurich, Zurich, Switzerland.
authors.forename: Jessica
authors.initials: J
authors.lastname: Kind
authors.affiliation: Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland; Centro Universitario de la Defensa, Zaragoza, Spain.
authors.forename: Inés
authors.initials: I
authors.lastname: García-Rubio
authors.affiliation: Plant and Microbial Biology, University of California, Berkeley, California.
authors.forename: Arash
authors.initials: A
authors.lastname: Komeili
authors.affiliation: Institute of Geophysics, ETH Zurich, Zurich, Switzerland. Electronic address: agehring@erdw.ethz.ch.
authors.forename: Andreas U
authors.initials: AU
authors.lastname: Gehring
mesh_terms: D016880:Anisotropy; D003901:Desulfovibrio / Q000187:drug effects / Q000378:metabolism*; D052203:Ferrosoferric Oxide / Q000494:pharmacology*; D060526:Magnetic Fields; D058185:Magnetite Nanoparticles / Q000737:chemistry*
chemical_list: D058185:Magnetite Nanoparticles; D052203:Ferrosoferric Oxide