magnetosome

Magnetosomes are intracellular, membrane-bounded organelles found in magnetotactic bacteria. Each magnetosome consists of a lipid-bounded vesicle in the cytoplasm that contains a single magnetite (Fe3O4) or greigite (Fe3S4) crystal. The crystals are highly uniform in size and shape and are arranged in one or more chains that span the cell, forming a magnetic dipole that helps orient the bacterium in the geomagnetic field.

Formation is genetically controlled by magnetosome gene clusters, often referred to as magnetosome islands, containing numerous mam and mms genes (for example mamA, mamB, mamK, mamJ, etc.). The vesicles invaginate from the cytoplasmic membrane and become magnetosome membranes; iron uptake, crystallization, and membrane organization yield magnetite or greigite crystals with high purity and controlled crystallography.

Ecologically, magnetotactic bacteria inhabit freshwater and marine sediments, typically under microaerophilic conditions. The magnetic chain aligns with the Earth's field, enabling movement toward the oxic-anoxic interface, where oxygen and nutrients balance best for growth.

Biomineral properties include single-domain magnetic crystals with diameters in the tens of nanometers, providing high magnetic stability. In sediments, preserved magnetosome crystals form magnetofossils that contribute to paleomagnetic records.

Potential applications are explored in nanotechnology and biomedicine, including targeted drug delivery, MRI contrast enhancement, and magnetic separation, leveraging the uniform size and biocompatibility of biologically produced magnetite.

Discovered in the 1970s by researchers studying microbial magnetism, magnetotactic bacteria and their magnetosomes have become a model for controlled biomineralization and bioinspired nanomaterials.