Magnetosome

Fig. 17.4 Magnetobacterium bavaricum from lake Chiemsee, Bavaria with four double rows of bullet-shaped magnetosomes (courtesy Dr. M. Hanslick, Munich)...

Fig. 17.6 Left hand side Model for the formation of magnetite in a Magnetospirillum species. L stands for an organic ligand. The oval forms represent specific Fe transport proteins, Right hand side Three magnetosomes encapsulated by a membrane (slightly modified) (Courtesy D. Schuler MPI Bremen see Schuler, 1999 A/ith permission).

Schuler D. (1999) Formation of magnetosomes in magnetotactic bacteria. J. Molec. Microbiol. BioTechn. 1 79-86 Schuler D. (2000) Characterization of magneto-some membrane in Magnetospirillum gryphiswaldense. In Bauerlein, E. (ed.) Biomineralization, 109-118... 

Vali, H. Kirschvink, J.L. (1991) Observations of magnetosome organization, surface stmc-ture, and iron biomineralization of undescribed magnetic bacteria Evolutionary speculations. In Frankel, R.B. Blakemore, R.P. (eds.) Iron biominerals. Plenum Press, New York, 97-115... 

Magnetotactic soil bacterium containing 36 magnetite-containing magnetosomes. Courtesy of Dennis Bazylinski. 

D. Schuler, Characterization of the Magnetosome Membrane in Magnetospirillum gryphiswaldense, in Biomineraliza-tion, from Biology to Biotechnology and Medical Application , ed. E. Baeuerlein, Wiley-VCH, Weinheim, 2000, p. 109. 

Figure 32.38. Magnetotactic Bacterium. The magnetosome, visible as a chain of opaque membrane-bound magnetite crystals, acts as a compass to orient the bacteria with the earth s magnetic field. The bacterium is artificially colored. [Courtesy of Richard B. Frankel, California Polytechnic State University, San Luis Obispo, California.]...

The crystallites grow within an organic membrane bound vesicle, or sac, the magnetosome. First a precursor iron oxide forms that matures into a single magnetic domain crystal of a magnetic iron mineral (Balkwill et al., 1980 Mann, 1985). The morphology of the individual crystallites is... 

The single-crystal nature of the majority of bacterial magnetites implies that nucleation of magnetite from the iron(III) precursor phase occurs at one primary nucleation site that grows at the expense of other potential sites. It is probable, therefore, that the surrounding magnetosome membrane plays a crucial role in the generation of a local environment for site-directed nucleation. One possibility is that... 

On the basis of these in vitro observations, it seems probable that the immature bacterial crystals develop through phase transformation processes involving a solution interface between the crystalline and amorphous phases. Initially, the amorphous phase is the kinetically favored product resulting from iron(II) oxidation. Continual flux of iron(II) across the magnetosome membrane will result either in additional ferric oxide formation or reaction of iron(II) with the preexisting iron(III) phase to give magnetite within the vesicle. The second pathway becomes competitive with a continual increase in iron(II) influx. 

Although magnetotactic bacteria (MTB) have diverse morphologies, they are characterised by the clustering of the genes required for magnetosome formation (Komeili, 2007 Matsunaga and Okamura, 2003), which are... 

It is striking to see the vast difference in the degree of complexity required to carry out the biomineralisation of magnetite in magnetosomes when we compare it to the relative simplicity of that of ferritin. 

Jogler, C., Schuler, D. (2009). Genomics, genetics, and cell biology of magnetosome formation. The Annual Review of Microbiology, 63, 501-521. 

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