Abstract
Magnetotactic bacteria are aquatic microorganisms with the ability to swim along the field lines of a magnetic field, which in their natural environment is provided by the magnetic field of the Earth. They do so with the help of specialized magnetic organelles called magnetosomes, vesicles containing magnetic crystals. Magnetosomes are aligned along cytoskeletal filaments to give linear structures that can function as intracellular compass needles. The predominant viewpoint is that the cells passively align with an external magnetic field, just like a macroscopic compass needle, but swim actively along the field lines, propelled by their flagella. In this minireview, we give an introduction to this intriguing bacterial behavior and discuss recent advances in understanding it, with a focus on the swimming directionality, which is not only affected by magnetic fields, but also by gradients of the oxygen concentration.
Highlights
The magnetic field of the Earth has been key to human navigation for about 1000 years, but it is used for navigation by animals such as migrating birds and fish [1]
This behavior, called magnetotaxis, is found in magnetotactic bacteria, a phylogenetically diverse group of aquatic bacteria [2, 3]. These bacteria align along magnetic fields with the help of a chain of organelles containing magnetic nanoparticles, which acts as a compass needle, and swim along the field lines with the help of their flagella
We will focus on magnetotactic bacteria as microswimmers that respond to directional clues and that may be steered with external fields
Summary
The magnetic field of the Earth has been key to human navigation for about 1000 years, but it is used for navigation by animals such as migrating birds and fish [1]. They provide ideal model systems to study how generic physical fields (the magnetic fields) work together with specific biological control mechanisms: Importantly, magnetism provides new biological functions, and imposes new constraints that the cells have to deal with In this minireview, we will focus on magnetotactic bacteria as microswimmers that respond to directional clues and that may be steered with external fields. Size and shape of the magnetic nanocrystals are tightly controlled by an array of proteins that are associated with the magnetosomes The genes encoding these proteins are mostly located in one genomic region of 130 kb, the so-called magnetotactic island [20]. The magnetosome particles are attached to a cytoskeletal structure, the so-called magnetosome filament [24, 25] This filament extends along the long axis of the cell. 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 have dynamic roles in the formation and positioning of the magnetosome chain [23, 27]
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