Elastic properties of magnetosome chains

Abstract

Magnetotactic bacteria swim and orient in the direction of a magnetic field thanks to the magnetosome chain, a cellular 'compass needle' that consists of a string of vesicle-enclosed magnetic nanoparticles aligned on a cytoskeletal filament. Here we investigate the mechanical properties of such a chain, in particular the bending stiffness. We determine the contribution of magnetic interactions to the bending stiffness and the persistence length of the chain. This contribution is comparable to, but typically smaller than the contribution of the semiflexible filament. For a chain of magnetic nanoparticles without a semiflexible filament, the linear configuration is typically metastable and the lowest energy structures are closed chains (flux closure rings) without a net magnetic moment that are thus not functional as a cellular compass. Our calculations show that the presence of the cytoskeletal filament stabilizes the chain against ring closure, either thermodynamically or kinetically, depending on the stiffness of the filament, confirming that such stabilization is one of the roles of this structure in these bacterial cells.

Magnetotactic bacteria

“…Another protein important for the chain structure is MamJ, which is believed to act as a linker between the magnetosomes and the filament (and possibly also between neighboring magnetosomes). One role of the filament is to stabilize the magnetosome chain in the straight configuration [26], but the polymerization and/or depolymerization of the filament may also have dynamic roles in the formation and positioning of the magnetosome chain [23,27].…”

Buckling of elastic filaments by discrete magnetic moments

“…Plugging in biological values [8], which in our notation can be given as µ 0 /(4π)m we see that buckling is only relevant for filament lengths < c ≈ 100 nm which is within the biologically relevant scale, thus indicating need for a stiff filament such as MamK. However, this is also notably close to the size of typical magnetosomes.…”

“…[1,3] The magnetic interaction between the attached particles can lead to a change in the elastic properties of the system. For an elastic filament this has been found to lead to a magnetic contribution [7,8] to the bending rigidity of the filament, analogously to the electrostatic contribution [9] for polyelectrolytes. Naturally occurring examples of such structures are magnetosome chains in magnetotactic bacteria [10].…”

The Effect of Sonication on Acoustic Properties of Biogenic Ferroparticle Suspension

“…This can be explained by the increase in adiabatic compressibility -the stiffness of the medium containing the chains of particles is greater due to the magnetic dipole-dipole interaction between particles in the chain that favors straight chain orientation and the elastic contribution due to the bending stiffness of the actin-like cytoskeletal filament to which the magnetosomes are attached (Kiani et al, 2015). Kiani's et al (2015) analysis shows that while both contributions are relevant, the bending stiffness of the filament can usually be expected to be the dominant part, with an about four-fold longer persistence length than due to the magnetic interaction alone. The measurement of the ultrasound velocity and attenuation as a function of temperature and frequency of the wave in the magnetic field of different intensities was carried out using the pulse method and the FFT analysis of the signals.…”

“…ticles are small enough to form a single magnetic domain, which means that they still possess a permanent magnetic moment. A general problem with these systems is that chain-like assemblies of magnetic nanoparticles are not stable and often collapse into clusters and closed-ring structures (Kiani et al, 2015) to minimize their magnetic stray field energy (Timko et al, 2008). The single magnetosomes (monodomain nanomagnets) were obtained after sonication ( Fig.…”