OCCURRENCE OF MAGNETIC BACTERIA IN SOIL

ENRICHMENT of the ferrimagnetic minerals magnetite and maghemite is frequently observed in the top layer of soil horizons1-5. Although both inorganic6,7and organic8,9processes are known to produce magnetite, magnetite in soils has been ascribed to an inorganic origin6. We report here the discovery of living magnetic bacteria, similar to those found in salt- and fresh-water sediments8,10-2, in the A horizon of a well developed soil profile in a typical meadow environment in southern Bavaria. The bacteria were detected in fresh samples using an optical microscope equipped with a rotating magnetic field13 and a volumetrically calibrated depression slide, permitting accurate counts of the volume density of the organisms. We suggest that magnetic bacteria and their magnetofossils14 can contribute to the magnetic properties of soils. © 1990 Nature Publishing Group.