Abstract
Understanding the biological processes enabling magnetotactic bacteria to maintain oriented chains of magnetic iron-bearing nanoparticles called magnetosomes is a major challenge. The study aimed to constrain the role of an external applied magnetic field on the alignment of magnetosome chains in Magnetospirillum magneticum AMB-1 magnetotactic bacteria immobilized within a hydrated silica matrix. A deviation of the chain orientation was evidenced, without significant impact on cell viability, which was preserved after the field was turned-off. Transmission electron microscopy showed that the crystallographic orientation of the nanoparticles within the chains were preserved. Off-axis electron holography evidenced that the change in magnetosome orientation was accompanied by a shift from parallel to anti-parallel interactions between individual nanocrystals. The field-induced destructuration of the chain occurs according to two possible mechanisms: (i) each magnetosome responds individually and reorients in the magnetic field direction and/or (ii) short magnetosome chains deviate in the magnetic field direction. This work enlightens the strong dynamic character of the magnetosome assembly and widens the potentialities of magnetotactic bacteria in bionanotechnology.
Highlights
Since their discovery more than 30 years ago, magnetotactic bacteria have received much attention in the fields of geological, chemical, physical and biological sciences[1,2,3,4,5]
AMB-1 cells were cultivated in presence of 20 μM of ferric quinate allowing for the production of magnetosomes
After one day of encapsulation of a bacterial suspension in an aqueous silica gel, the ultrastructure of the bacteria remained well preserved (Fig. 1b) and scanning electron microscopy (SEM) images showed that the cells were well dispersed in the porous mineral network (Fig. 1c)
Summary
Since their discovery more than 30 years ago, magnetotactic bacteria have received much attention in the fields of geological, chemical, physical and biological sciences[1,2,3,4,5]. The chain deviation was shown to be reversible when the field was turned off, suggesting that the assembly of proteins involved in the nanocrystal organization had a dynamic character These intriguing observations opened many additional questions such as the effect of chain re-orientation on cell viability as well as its impact on the crystallographic and magnetic orientation of the nanoparticles. Aiming to go further in the understanding of these processes, we have used here a mineral matrix, made of hydrated silica, as an encapsulation host for the AMB-1 magnetotactic bacteria, in order to prevent their motility in presence of an external magnetic field This mineral matrix can be obtained in water, near neutral pH and at room temperature[35]. Bacteria are confined in a cavity adapted to their size, preventing their motility, and cell division is hindered to insure that the population remains constant over the whole experiment[37]
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