ISTerre seminar

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Magnetic nanoparticles in organisms: From bacteria to the human brain

Tuesday 20 May 2025 - 10h30

Leon Kaub - udwig-Maximilians-Universität München (LMU Munich)
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Magnetite (Fe3O4) nanoparticles are ubiquitous in the environment. They are formed in igneous and metamorphic environments and are emitted from anthropogenic processes such as coal combustion and traffic. Magnetite particles are also biomineralized by microbes in soil and sediments and have even been found in tissues including the human brain. The most studied magnetite-producing organisms are magnetotactic bacteria (MTB), which use magnetite for an alignment with the geomagnetic field that guides them to their preferred habitat. While the biomineralization processes in MTB are well understood, the presence of magnetite in the brain remains enigmatic. Particles may be produced in the brain through controlled biomineralization, such as in MTB, but could also originate from imbalanced iron metabolism, or reach the brain from the outside environment as air pollution. Our magnetic measurements of postmortem human brain stems and the surrounding meninges argue for an external origin of magnetite and its translocation via blood. Extremely high magnetite levels in the brain of a subject with liver cirrhosis and hepatic iron overload support the hypothesis that blood is the main carrier. Furthermore, we found a constant concentration of single-domain magnetite in the brain with age, which could argue for internal biomineralization, but is rather explained by clearance processes that lead to steady-state magnetite levels. An observed increase in superparamagnetic particle content in individuals over 50 implies reduced clearance mechanisms in older individuals. Overall, most magnetite nanoparticles in the brain appear to undergo dynamic processes to reach and enter the brain after circulating in blood. This is concerning due to their high redox activity and surface charge, which has the potential to significantly impact health.

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Organizing team : Minéralogie et Environnements

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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