Magnetotactic bacteria and magnetosomes: biomineralization, biomarkers and biomagnetism

Résumé : Magnetotactic bacteria (MTB) are motile aquatic prokaryotes that have the ability to navigate along the Earth's magnetic field. This so-called magnetotaxis is a result of the presence of magnetosomes, organelles which comprise nanometer-sized intracellular crystals of magnetite (Fe3O4) enveloped by a membrane. Particles resembling magnetosomes crystals were discovered in the Martian meteorite ALH84001, and therefore the magnetosomes were used as a signature of life raising the interest for these organisms although they were already discovered for 30 years. In general, little is known about the methods by which bacteria synthesize these mineral crystals, although there has been a good deal of progress in our understanding of some of the specific features of magnetosomes and how they function within cells. In our lab, the synthesis of the bacterial magnetosome is not only tackled down at the genetic level, but we also employ molecular and physico-chemical techniques. Thus, some results will be presented, showing the particular role of the MamJ proteins in magnetosomes arrangement, demonstrating that environmental parameters influence the crystal properties and therefore preventing the use of magnetosomes as biomarker, and finally showing the evolution of the magnetic properties of he bacteria with respect to crystals size and inter-particle distances. -------------------------------------------------------------------------------- Séminaires Géomatériaux et Environnement --------------------------------------------------------------------------------