MAGNETIC IRON-SULFUR CRYSTALS FROM A MAGNETOTACTIC MICROORGANISM

IN all magnetotactic microorganisms studied so far, the geomagnetic field is detected by magnetic particles with a permanent magnetic moment. These are crystallites enveloped by a membrane that forms the magnetosome, a specialized organelle common to magnetotactic cells1,2. To date, the magnetic crystallite of magnetotactic bacteria has been found to be magnetite, an iron-oxygen mineral3-7. Here we report the discovery of magnetic iron-sulphur crystals in a highly motile multicellular aggregate of bacteria found in brackish water with sulphide-rich sediments. The iron sulphide crystals are enveloped by amorphous or weakly crystalline regions rich in iron and oxygen, and these regions are surrounded by a membrane forming the magnetosome. The oxygen-rich region may be involved in growth of the iron sulphide crystals. The magnetosomes are found in planar groups inside the cytoplasm of each cell in the aggregate. Magnetic iron sulphide such as we describe here, which is probably pyrrhotite, may be a source of remnant magnetization in sediments and soils. © 1990 Nature Publishing Group.