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Journal of Bacteriology, June 2006, p. 3805-3812, Vol. 188, No. 11
0021-9193/06/$08.00+0     doi:10.1128/JB.00020-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Spatial Localizations of Mam22 and Mam12 in the Magnetosomes of Magnetospirillum magnetotacticum

Department of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan,¹ Laboratoire de Chimie Bactérienne (LCB), UPR9043, IBSM, CNRS, 31, chemin Joseph Aiguier, 13402 Marseille Cedex 20, France²

Received 8 January 2006/ Accepted 15 March 2006

Magnetospirillum magnetotacticum possesses intracellular magnetite particles with a chain-like structure, termed magnetosomes. The bacterium expresses 22-kDa and 12-kDa magnetosome-associated proteins, termed Mam22 (MamA) and Mam12 (MamC), respectively. In this study, we investigated the structure of the purified magnetosomes with transmission electron microscopic techniques and found that the magnetosomes consisted of four compartments, i.e., magnetite crystal, magnetosomal membrane, interparticle connection, and magnetosomal matrix. Furthermore, we determined the precise localizations of Mam22 and Mam12 using immunogold staining of the purified magnetosomes and ultrathin sections of the bacterial cells. Interestingly, most Mam22 existed in the magnetosomal matrix, whereas Mam12 was strictly localized in the magnetosomal membrane. Moreover, the recombinant Mam22 was attached to the magnetosomal matrix of the Mam22-deficient magnetosomes prepared by alkaline treatment, such as 0.1 M Caps-NaOH buffer (pH 11.0). The spatial localization of the magnetosome-associated proteins in the magnetosomal chain provides useful information to elucidate the functional roles of these proteins.

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