Molecular and Biotechnological Aspects of Bacterial Magnetite

Magnetic bacteria synthesize intracellular magnetosomes consisting of magnetite (Fe3O4) or greigite (Fe3S4) that vary in from 50 to 100 nm. Magnetosomes are aligned in chains parallel to the cell axis, enabling the cell to migrate along the Earth's geomagnetic field lines and to maintain its position within the boundary of the oxic-anoxic transition zone (OATZ) [for review, see 1]. This magnetotaxis is associated with aerotactic sensory mechanisms [2]. However, facultative anaerobic Magnetospirillum magneticum AMB-1 and MGT-1 exhibit relatively less magnetotaxis. Thus, we refer to these strains as «'magnetic'» rather than magnetotactic. Magnetosomes are also referred to as bacterial magnetic particles (BMPs) to distinguish them from artificial magnetic particles (AMPs). The aggregation of BMPs can be easily dispersed in aqueous solutions compared to AMPs because of the enclosing membrane (Figure 6.1) [3]. In addition, the particle is the largest magnetic crystal that has a regular morphology within a single domain size. Therefore, BMPs have a vast potential for various technological applications, not only scientific interests. However, the molecular mechanism of magnetite biomineralization is poorly understood although iron oxide formation occurs widely in many organisms such as algae [4], chitons [5], honey bee [6, 7], yellowfin tuna [8], sockeye salmon [9, 10], etc. We are currently using M. magneticum AMB-1 (Figure 6.2A), for which gene transfer techniques have been developed [11], as a model organism in order to elucidate the molecular mechanisms of magnetite biomineralization. Here, we describe several findings and application studies for BMPs in M. magneticum AMB-1.