Research Article: Formation of Core-Shell Nanoparticles Composed of Magnetite and Samarium Oxide in Magnetospirillum magneticum Strain RSS-1

Date Published: January 26, 2017

Publisher: Public Library of Science

Author(s): Hirokazu Shimoshige, Yoshikata Nakajima, Hideki Kobayashi, Keiichi Yanagisawa, Yutaka Nagaoka, Shigeru Shimamura, Toru Mizuki, Akira Inoue, Toru Maekawa, Bing Xu.


Magnetotactic bacteria (MTB) synthesize magnetosomes composed of membrane-enveloped magnetite (Fe3O4) or greigite (Fe3S4) particles in the cells. Recently, several studies have shown some possibilities of controlling the biomineralization process and altering the magnetic properties of magnetosomes by adding some transition metals to the culture media under various environmental conditions. Here, we successfully grow Magnetospirillum magneticum strain RSS-1, which are isolated from a freshwater environment, and find that synthesis of magnetosomes are encouraged in RSS-1 in the presence of samarium and that each core magnetic crystal composed of magnetite is covered with a thin layer of samarium oxide (Sm2O3). The present results show some possibilities of magnetic recovery of transition metals and synthesis of some novel structures composed of magnetic particles and transition metals utilizing MTB.

Partial Text

Magnetotactic bacteria (MTB) form intracellular chains of magnetosomes, which contain membrane-enveloped magnetic crystals comprised of magnetite (Fe3O4) or greigite (Fe3S4) [1,2]. The size of magnetosomes ranges from 35 to 120 nm, and the shape varies depending on the bacterial strains. The size and shape are, however, highly uniform in each strain [3–5]. The biomineralization process is strictly controlled by the magnetosome-related genes. Such a high degree of control of the synthetic process of magnetosomes occurring in MTB has a significant advantage over the other synthetic methods of magnetic nanoparticles particularly in terms of the morphological definition and biocompatibility [6–9]. Magnetosomes are of great importance considering their application to nanotechnology-based biomedical studies; e.g., they can be used as nano magnetic resonance imaging enhancing agents, nano hyperthermic cancer treatment media and nano drug delivery vehicles [10], the performances of which are however totally dependent on the magnetic properties of the magnetosomes.

It had been assumed that lanthanides can be bound to the cell surface of bacteria, but they cannot be transported into the cytoplasm of bacteria [21,49]. However, it was shown that lanthanum and terbium accumulate in the periplasmic space of Escherichia coli [23], which suggests that lanthanides may be transported into the periplasmic space of MTB, knowing that all of MTB possess a cell wall structural characteristic of gram-negative bacteria [7].




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