Magnetotactic Bacteria at the Earth-Life-Materials Interface

Conspectus Magnetotactic bacteria (MTB) are prokaryotes that biomineralize membrane-bound intracellular magnetite (Fe3O4) or greigite (Fe3S4) nanocrystals, termed magnetosomes. These crystals commonly form chains that function as nanoscale compass needles. As naturally evolved living magnetic nanomaterial systems, MTB connect intracellular biomineralization, magnetic-field-guided behavior, microbial ecology, geological recording, and biomimetic materials design. Their hierarchical magnetosome architecture couples weak geomagnetic fields to cellular magnetic torque, directed motility, and redox-niche positioning, while preserved magnetosomes can enter sedimentary records as magnetofossils. This Account traces MTB from modern cells to ancient rocks and engineered materials. We first show how correlative single-cell microscopy, sequencing, and magnetic analyses link uncultured lineages with cell morphology, magnetosome crystal habit, chain architecture, genomic background, and magnetic properties, extending MTB research beyond a few cultivable models. These studies reveal that magnetosome biomineralization is genetically constrained yet environmentally responsive, providing a reference framework for magnetofossil interpretation and biomimetic magnetic-material design. We next extend the view of MTB beyond magnetosome production. Many MTB also accumulate nonmagnetic mineral and storage phases containing sulfur, phosphorus, silicon, carbonates, and trace metals. Their coexistence with magnetosomes indicates that magnetic navigation is embedded within broader cellular processes involving redox metabolism, nutrient storage, metal homeostasis, and environmental adaptation. MTB can therefore be viewed as intracellular biogeochemical reactors at aquatic redox interfaces, where geomagnetic-field-guided movement may facilitate repeated access to separated oxidants and reductants. Magnetosomal magnetic particles are also geologically important as nanoscale magnetic fossils. When sufficiently preserved, magnetofossils can constitute a “triple archive” of paleomagnetic information, paleoenvironmental redox conditions, and ancient microbial activity. Realizing this potential requires quantitative, carrier-resolved identification in complex magnetic mineral assemblages. We therefore emphasize workflows combining rock magnetism with microscopy, crystallography, nanoscale chemical analysis, and calibration against modern MTB to distinguish biogenic signals from detrital, authigenic, and diagenetic overprints and assess magnetofossil preservation. Finally, we frame MTB and magnetosome systems as a cross-scale platform for functional magnetic materials. At the particle scale, magnetosome core chemistry, crystal morphology, and membrane interfaces can be modified through controlled cultivation, chemical substitution, genetic programming, and heterologous biosynthesis. At the chain scale, regulated particle size, spacing, alignment, and dipolar interactions generate collective anisotropy and strong field responsiveness. At the cellular scale, self-propulsion, magnetic steerability, and preferential migration toward low-oxygen microenvironments enable living and biohybrid microrobotic functions. These hierarchical design principles are being translated into magnetic imaging and sensing, hyperthermia and targeted delivery, and magnonics and nanomagnetic devices. Together, this Earth-life-materials perspective shows how biologically produced magnetic nanostructures mediate microbial interaction with the geomagnetic field, preserve records of Earth-life processes, and inspire next-generation magnetic technologies. Major challenges are to expand coverage beyond model strains, improve genetic access to diverse MTB, validate magnetofossils in situ in ancient rocks, resolve chain alteration during burial, and translate biological control into scalable, reproducible materials platforms.