Bacteria with motility directed by the local geomagnetic field have been observed in marine sediments. These magnetotactic microorganisms possess flagella and contain novel structured particles, rich in iron, within intracytoplasmic membrane vesicles. Conceivably these particles impart to cells a magnetic moment. This could explain the observed migration of these organisms in fields as weak as 0.5 gauss.

Intact magnetosomes of Aquaspirillum magnetotacticum were purified from broken cells by a magnetic separation technique. Electron microscopic and chemical analyses revealed the magnetite to be enclosed by a lipid bilayer admixed with proteins. Lipids were recovered in fractions expected to contain (i) neutral lipids and free fatty acids, (ii) glycolipids and sulfolipids, and (iii) phospholipids (in a weight ratio of 1:4:6). Phospholipids included phosphatidylserine and phosphatidylethanolamine. Two of the numerous proteins detected in the magnetosome membrane were not found in other cell membranes or soluble fractions.

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The 16s rRNA gene of the magnetotactic magnetogen Aquaspirillum magnetotacticum MSl was amplified by a polymerase chain reaction, using two eubacterial consensus oligodeoxynucleotide primers flanking the majority of the 16s rRNA gene, cloned, and sequenced. Phylogenetic analysis revealed that A . magnetotacticum MS1 belongs to the a-group of proteobacteria. This assignment offers perspective on the biochemical properties of A. magnetotacticum, since this organism is expected to have the general properties that are common to this phylogenetic group.