Magnetotactic bacteria and their nanomagnets

Magnetotactic bacteria are mobile, gram-negative prokaryotes that biosynthesize intracellular crystals of iron oxide or sulfide. These magnetic nanocrystals are surrounded by a membrane and aligned in a chain in the bacterium's cytoplasm. They are then called "magnetosomes" and enable the cell to orient itself and swim along lines of magnetic field, whether artificial or terrestrial. Richard Blakemore first described magnetosomes in magnetotactic bacteria in 1975 .

Magnetotactic bacteria are ubiquitous microorganisms found in aquatic sediments or the column of stratified water bodies, mainly in the oxic-anoxic transition zone or just below, in the anoxic zone. They can be found in both seawater and freshwater. This group of prokaryotes is morphologically, phylogenetically and physiologically highly diverse. However, only a few magnetotactic bacteria have been isolated in pure culture, and little is known about their metabolic plasticity. At present, the best described magnetotactic species belong to the Magnetospirillum genus. Representatives of this genus are reproducibly grown in large quantities, and most of them can be genetically manipulated. Thus, most of our fundamental knowledge of the metabolism, genetics and biochemistry of magnetotactic bacteria comes from studies carried out on species belonging to this genus. Magnetospirillum are also at the origin of numerous studies exploiting the potential of magnetotactic bacteria, or just their magnetosomes, for biotechnological applications.

In this article, we will present the state of fundamental knowledge on the biodiversity of magnetotactic bacteria and the molecular mechanisms involved in synthesizing the crystals they biomineralize. The potential uses of magnetotactic bacteria in fields such as geology and biotechnology will then be detailed.