A Bacterial Backbone: Magnetosomes in Magnetotactic Bacteria

Abstract

Magnetosomes are intracellular, tens of nanometer-sized, membrane-bounded crystals of the magnetic minerals magnetite (Fe3O4) and greigite (Fe3S4) synthesized by a diverse group of prokaryotes termed the magnetotactic bacteria. These unusual microorganisms biomineralize magnetosomes via a biologically controlled biomineralization process where the composition, size and morphology of the mineral crystals are under fine chemical, biochemical and genetic controls. Magnetosomes are most often arranged as a chain within the cell and they provide a permanent magnetic dipole moment to the cell causing it to passively align along magnetic field lines like a compass needle. Magnetotaxis is the result of this passive alignment while the cell swims. The magnetotactic bacteria presumably utilize magnetotactic in conjunction with chemotaxis (e.g., aerotaxis) to locate and maintain an optimal position in vertical chemical and/or redox gradients in natural habitats. The locus of biomineralization of magnetosome crystals is the magnetosome membrane vesicle which contains proteins that are unique to it that are not found in other parts of the cell. The roles of some of these magnetosome membrane proteins in the biomineralization process and the construction of the magnetosome chain have been determined while the roles of most have not. The genes that encode for magnetosome membrane proteins are located in clusters in a magnetosome gene island in many magnetotactic bacteria that also contain a number of mobile elements suggesting the island can be transferred to different bacteria via horizontal gene transfer. Magnetosome crystals possess novel magnetic properties that have been exploited in numerous applications and are important in biotechnology.