Cell Biology of Magnetosome Formation

Magnetosome chains are the intracellular structures that allow magnetotactic bacteria to align in and navigate along geomagnetic fields (Bazylinski and Frankel 2004). These organelles are typically defined as a unit consisting of a magnetite or greigite crystal surrounded by a lipid bilayer membrane (Balkwill et al. 1980). Although these magnetic minerals are the usual targets of most studies of magnetotactic bacteria it is the magnetosome membrane that fascinates cell biologists. One of the cornerstones of cell biology has been that membrane-bound organelles are unique to eukaryotes. However, it is now known that membranous organelles exist in many prokaryotes raising the possibility that the endo-membrane system of eukaryotic cells might have originated in prokaryotes (Jetten et al. 2003; Seufferheld et al. 2003; Fuerst 2005). Magnetosomes are one of the best-studied examples of these prokaryotic organelles with the potential to be an ideal system for the study of organelle development in prokaryotes. This work provides a review of the current knowledge of magnetosomes from a cell biological perspective focusing on the composition and formation of the magnetosome membrane and the cytoskeletal framework organizing individual magnetosomes into chains.