Chapter 4 A Bacterial Backbone: Magnetosomes in Magnetotactic Bacteria Christopher T. Lefe `vre, Fernanda Abreu, Ulysses Lins, and Dennis A. Bazylinski 4.1 Introduction One of the most intriguing discoveries in the realm of microbiology was that of the phenomenon known as magnetotaxis and the magnetotactic bacteria. Magnetotactic bacteria are prokaryotes that passively align and actively swim along magnetic field lines (Bazylinski and Frankel 2004). They were apparently first described by Salvatore Bellini in 1963 in an obscure publication of the Instituto di Microbiologia of the University of Pavia, Italy (Bellini 2009a, b). He microscopically observed bacteria that swam towards the North Pole and hence called them “baterri magne- tosensibili” (magnetosensitive bacteria) and believed that cells had an internal magnetic compass that was responsible for his observations although he never proved this point. Blakemore (1975), independently, rediscovered these organisms in 1974 and coined the terms magnetotaxis for the phenomena and magnetotactic bacteria for the microorganisms. Moreover, he uncovered and described the internal compass of Bellini: the magnetosome, the subject of this chapter. The magneto- some is defined as internal, membrane-bounded single-magnetic domain crystals of a magnetic mineral that is either an iron oxide or iron sulfide (Balkwill et al. 1980; Gorby et al. 1988). The goal of this chapter is to review what is known regarding the bacterial magnetosome as to its function and how it is biomineralized by magnetotactic bacteria. In addition, we also describe the significance of magnetosomes and magnetosome mineral crystals in biotechnological applications. C.T. Lefe `vre and D.A. Bazylinski (*) School of Life Sciences, University of Nevada at Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4004, USA e-mail: christopher.lefevre@unlv.edu; dennis.bazylinski@unlv.edu F. Abreu and U. Lins Instituto de Microbiologia Professor Paulo de Go ´es, Universidade Federal do Rio de Janeiro, 21941-590 Rio de Janeiro, Brazil e-mail: abreufernandadeavila@hotmail.com; ulins@micro.ufrj.br M. Rai and N. Duran (eds.), Metal Nanoparticles in Microbiology, DOI 10.1007/978-3-642-18312-6_4, # Springer-Verlag Berlin Heidelberg 2011 75