Magnetotactic

Magnetotactic describes organisms that navigate using Earth's magnetic field. The term is most often applied to magnetotactic bacteria (MTB), a diverse group of aquatic bacteria that synthesize intracellular magnetic mineral crystals called magnetosomes. Magnetosomes typically contain magnetite (Fe3O4) or greigite (Fe3S4) and are organized into chains inside a membrane-bound compartment, effectively functioning as a cellular compass.

In response to geomagnetic fields, MTB exhibit magnetotaxis, a biased movement toward favorable environmental conditions. The magnetosome chain biases swimming direction, helping cells locate optimal redox zones in sediments where oxygen, nutrients, and redox potential balance. Motility is achieved by flagella, and magnetosome formation is guided by conserved gene clusters known as magnetosome islands that encode proteins for biomineralization and chain assembly.

Taxonomy and ecology: MTB have been isolated from several bacterial lineages, with well-studied species such as Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. They are common in freshwater and marine sediments, often in microaerobic niches. The ability to biomineralize magnetosomes appears to be ancestrally acquired in diverse groups and is a topic of interest for understanding the evolution of magnetotaxis.

Applications and significance: Magnetosomes are uniform in size and magnetic properties, making them attractive for nanotechnology and biomedicine. Potential uses include magnetic separation, targeted drug delivery, magnetic resonance imaging contrast, and biosensing. Research continues to elucidate the mechanisms of magnetosome biomineralization, magnetotaxis signaling, and the ecological roles of MTB in sediment ecosystems.