Magnetite, bacterial

Eggar-Gibbs ZG, Jude B, Dominik J, Loizeau JL, Oldfield F (1999) Possible evidence for dissimilatory bacterial magnetite dominating the magnetic properties of recent lake sediments. Earth Planet Sci Lett 168 1-6... 

The details of enzymatic magnetite formation in bacteria, especially the valence and chemical form in which the Fe enters the cell, are still not fully understood. At low oxygen concentrations in the bacterial habitats dissolved Fe may exist in bivalent form, but Fe added as a soluble Fe " complex, such as Fe " citrate (Schuler Bauerlein, 1996) can also function as an Fe source. Within the cell, part of the Fe will then form a highly reactive Fe "oxide, probably ferrihydrite, which in turn, reacts with the dissolved Fe to form magnetite (Mann et al. 1989) by a via-solution process (Fig. 17.6) ... 

Petersen, N. von Dobeneck,T. Vali, H. (1986) Fossil bacterial magnetite in deep-sea sediments from the South Atlantic Ocean. Nature 320 611-615... 

Towe, K.M. Moench,T.T. (1981) Electron-optical characterization of bacterial magnetite. Earth Planet. Sci. Letters 52 213-220... 

The essential element iron is not only utilized by all living systems but bacteria materially assist the nucleation of minerals that contain ferric and ferrous forms. After a brief consideration of the roles of iron in bacterial systems, we discuss the magnetotactics, the bacteria that biomineralize with euhedral nanosized particles of magnetite, Fc304, and greigite, Fe3S4. 

Mann S. (1985) Structure, morphology, and crystal growth of bacterial magnetite. In Magnetite Biomineralization and Magnetoreception in Organisms (eds. J. L. Kirschvink, D. S. Jones, and B. J. MacEadden). Plenum, New York, pp. 311-332. 

Fig. 6. HRTEM lattice image of a bacterial magnetite ciystal from coccoid cells. The crystal is imaged along the [110] direction and has a characteristic rectangular shape when viewed in projection. Truncated faces are identified. Lattice fringes are 111, 4.85 A and 200, 4.2 A. Bar = 20 nm.

Fic. 7. Morphological forms of bacterial magnetite observed in projection, (a) Hexagonal (cubo-octahedral) (b) rectangular [note the twinned ciystal (arrow)] (c) cubic and (d) bullet shaped. In each case the crystals are oriented with the (111) faces perpendicular to the chain axis. Bars = 50 nm in all micrographs. 

Fig. 8. Idealized crystal morpliologies of bacterial magnetite, (a) cubo-oetahedron Aquaspirillum magnetotacticum)-, (b and c) hexagonal prisms (coccoid and vibrioid cells) (d) elongated cubo-octahedron (wild-type cells).

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. 

Matsunaga T, Sato R., Kamiya S, Tanaka T, Takeyama H. (1999). Chemiluminescence enzyme immunoassay using Protein A-bacterial magnetite complex. J. Magn. Magn. Mater. 268, 932-937. 

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