Abstract
Magnetotactic bacteria assemble chains of magnetosomes, organelles that contain magnetic nano-crystals. A number of genetic factors involved in the controlled biomineralization of these crystals and the assembly of magnetosome chains have been identified in recent years, but how the specific biological regulation is coordinated with general physical processes such as diffusion and magnetic interactions remains unresolved. Here, these questions are addressed by simulations of different scenarios for magnetosome chain formation, in which various physical processes and interactions are either switched on or off. The simulation results indicate that purely physical processes of magnetosome diffusion, guided by their magnetic interactions, are not sufficient for the robust chain formation observed experimentally and suggest that biologically encoded active movements of magnetosomes may be required. Not surprisingly, the chain pattern is most resembling experimental results when both magnetic interactions and active movement are coordinated. We estimate that the force such active transport has to generate is compatible with forces generated by the polymerization or depolymerization of cytoskeletal filaments. The simulations suggest that the pleiotropic phenotypes of mamK deletion strains may be due to a defect in active motility of magnetosomes and that crystal formation in magneteosome vesicles is coupled to the activation of their active motility in M. gryphiswaldense, but not in M. magneticum.
Highlights
Magnetotactic bacteria have the ability to orient and navigate in the magnetic field of the Earth with the help of special magnetic organelles called magnetosomes [1]
Model for magnetosome chain formation To study the driving forces of magnetosome chain formation, we developed a stochastic model describing the dynamics of magnetosomes in a bacterial cell (Figure 1)
The simulations show that diffusive movements of magnetosomes, guided by their magnetic interactions, are not sufficient for the robust formation of a single magnetosome chain that is observed experimentally in magnetotactic bacteria
Summary
Magnetotactic bacteria have the ability to orient and navigate in the magnetic field of the Earth with the help of special magnetic organelles called magnetosomes [1]. The generated magnetic dipole moment is large enough so that its interaction energy with the magnetic field of the Earth overcomes thermal fluctuations and allows cells to align and to swim along field lines The latter behavior is known as magnetotaxis [2] and is believed to direct the bacteria towards environmental conditions favorable for growth [3]. Magnetotactic bacteria have mostly been investigated in the context of environmental microbiology for their diversity in both phylogeny and habitats [4,5,6] and in geosciences, as fossil magnetosomes contribute to the magnetism of sediments [7] They have become model systems for biomineralization because of their specific crystal morphologies, their chemical purity and their quasi-one dimensional organization [8,9].
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