Muds from both freshwater and marine environments, as well as sewage treatment ponds, have included such talented micro-organisms. The magnet in these tiny cells is made up of 20 or so roughly cubic particles arranged in a line along the long axis of the cell. These particles are not only the appropriate size for their host cells, but in physical terms they represent the only design that would work as a magnet on this small scale. The particles are made of a type of iron oxide called magnetite or lodestone. In the laboratory it is difficult to make magnetite particles of this small size.
Biologists are unsure how the bacteria achieve such precision.
Anyone who has looked through the microscope at tiny objects suspended in water cannot fail to notice how they are all in constant vibrating motion, even in living cells. This 'Brownian' motion results from random jostling of molecules, and the warmer they are, the faster they move. The magnetite particles, however, must not be jostled by Brownian motion, otherwise there would be no magnetic orientation. Thus each particle must be able to orient itself firmly in the direction of the earth's magnetic field. Biologists believe that this ability may provide a mechanism to enable bacteria to orient themselves in space.