Magnetotaxis

Magnetotaxis is the directed movement or orientation of motile organisms in response to magnetic fields. It is best documented in magnetotactic bacteria, which align and swim along lines of the Earth's magnetic field to reach favorable chemical environments, particularly oxic–anoxic interfaces in sediments and in stratified bodies of water.

The primary mechanism involves magnetosomes, membrane-bound magnetic mineral crystals (usually magnetite Fe3O4, and sometimes greigite Fe3S4) that are organized into one or more chains inside the cell. The magnetosome chain acts like a compass needle, giving the cell a magnetic dipole that biases its orientation relative to the magnetic field. Coupled with the bacterium’s flagellar motility, this enables a biased random walk in which vertical or horizontal movement is biased toward preferred redox conditions, such as the transition from oxygen-rich to oxygen-poor zones.

Magnetotactic bacteria are diverse and found in freshwater and marine sediments worldwide. Their magnetosomes are produced under genetic control by magnetosome gene clusters, including families of genes such as mam and related magnetosome-associated operons, which coordinate biomineralization and chain assembly. This system supports efficient navigation in chemically stratified habitats, aiding the bacteria in locating optimal zones for growth and metabolism.

History and applications: Magnetotaxis was elucidated in the late 20th century with the study of magnetotactic bacteria. Beyond fundamental biology, magnetotactic magnetosomes have inspired research in nanotechnology and biomedicine, and ongoing work explores their ecological roles in nutrient cycling and sediment ecology.