Magnetotactic bacteria can orient and migrate along geomagnetic field lines because of their intracellular single-domain magnetic nano-crystal particles with biomembrane bounded,which are referred as magnetosomes. Magnetite Fe₃O₄ is the main chemical component of magnetosomes characterized by the high chemical purity, fine grain size uniformity, and good biocompatibility, which can be used as a new kind of nano-magnetic materials applied in many fields of biochemistry, magnetic materials, clinical medicine and wastewater treatment, and so on. Magnetosome formation is the mineralization process under strict biochemical mechanisms control, including four steps: iron accumulation, membrane formation, transportation and controlled biomineralization of Fe₃O₄. In this paper, the characteristics of magnetotactic bacteria, chemical composition, structure, synthesis conditions and mechanisms, magnetism, separation and purification, the applications of the nano-magnetic particles are summarized and reviewed. The main problems to be resolved and the prospects of magnetosomes are also presented.

Contents
1 Introduction
2 Magnetotactic bacteria
3 Chemical composition and morphology of magnetosomes
3.1 Chemical composition of magnetosomes
3.2 Morphology of magnetosomes
4 Synthetic conditions and biochemical mechanisms of magnetosomes
4.1 Synthetic conditions of magnetosomes
4.2 Synthetic processes and mechanisms of magnetosomes
5 Magnetic properties of magnetosomes in magnetotactic bacteria
5.1 Magnetic properties of magnetosomes
5.2 Effect of chains arrangement on magnetic properties
5.3 Effect of morphology and chemical composition on magnetic properties
6 Separation and purification of magnetosomes
7 Applications of magnetosomes in ralated fields
7.1 Application in sewage treatment
7.2 Application in medical treatment
7.3 Application in sensing technology
8 Biological and geoscience significance of biomineralization
9 Conclusions