Magnetosome chains are recruited to cellular division sites and split by asymmetric septation

Magnetotactic bacteria navigate along magnetic field lines usingwell-ordered chains of membrane-enclosed magnetic crystals, referred toas magnetosomes, which have emerged as model to investigate organellebiogenesis in prokaryotic systems. To become divided and segregatedfaithfully during cytokinesis, the magnetosome chain has to be properlypositioned, cleaved and separated against intrachain magnetostaticforces. Here we demonstrate that magnetotactic bacteria use dedicatedmechanisms to control the position and division of the magnetosomechain, thus maintaining magnetic orientation throughout divisionalcycle. Using electron and time-lapse microscopy of synchronized cells ofMagnetospirillum gryphiswaldense, we confirm that magnetosome chainsundergo a dynamic pole-to-midcell translocation during cytokinesis.Nascent chains were recruited to division sites also indivision-inhibited cells, but not in a mamK mutant, indicating an activemechanism depending upon the actin-like cytoskeletal magnetosomefilament. Cryo-electron tomography revealed that both the magnetosomechain and the magnetosome filament are spilt into halves by asymmetricseptation and unidirectional indentation, which we interpret in terms ofa specific adaptation required to overcome the magnetostaticinteractions between separating daughter chains. Our study demonstratesthat magnetosome division and segregation is co-ordinated withcytokinesis and resembles partitioning mechanisms of other organellesand macromolecular complexes in bacteria