Magnetite and Magnetotaxis in Microorganisms

Abstract

Magnetotactic bacteria include various species of aquatic microorganisms that orient and swim along magnetic field lines (Blakemore, 1975; 1982; Blakemore & Frankel, 1981; Moench & Konetzka, 1978). All magnetotactic cells examined to date by electron microscopy contain iron-rich, electron opaque particles (Balkwill et al. 1980; Towe & Moench, 1981). In several and possibly all species of magnetotactic bacteria, the particles consist of magnetite, Fe₃O₄, (Frankel et al., 1979). In most species the particles are arranged in chains, which impart a magnetic moment to the cell, parallel to the axis of motility. The moment is sufficiently large that the bacterium is oriented in the geomagnetic field at ambient temperature as it swims, i.e. the chain of Fe₃O₄ particles functions as a biomagnetic compass (Frankel & Blakemore, 1980). By this means the organism propels itself along the geomagnetic field lines. The direction of migration depends on the orientation of the biomagnetic compass. Those with north-seeking pole forward migrate north along the field lines. Those with the south-seeking pole forward migrate south. It has been found that north-seeking bacteria predominate in the Northern Hemisphere while south-seeking bacteria predominate in the Southern Hemisphere (Blakemore et al., 1980; Kirschvink, 1980).