Shingo Watanabe

Electron Spin Resonance Spectroscopic Study of Size-Controlled Ink Particles Isolated from Sepia officinalis

The paramagnetic properties of size-controlled ink particles isolated from the ink sacs of Sepia officinalis were studied by electron spin resonance (ESR) spectroscopy. Both the size-controlled ink particles and synthetic melanins seemingly yielded similar ESR spectra consisting of a singlet with a slightly asymmetrical signal. However, the progressive microwave power saturation revealed a clear difference between their paramagnetic behaviors. In comparison with synthetic melanins, the ESR spectra of the ink particles readily reached saturation, indicating a long spin–lattice relaxation time. On the other hand, the ESR linewidth depended on particle size. This implies that the particle size is related to the distance between paramagnetic species in the particles. Hence, it is reasonable that the large ink particle has the weakest spin–spin interaction among these samples. The employment of the size-controlled ink particles enabled us to determine precisely the paramagnetic parameters of Sepia inks.

Intracellular Distribution of Iron in the Cell of Magnetotactic Bacteria Inhibited the Biosynthesis of Magnetic Nano-Particles by Limiting the Iron Source

Magnetotactic bacteria are the bacteria which synthesize nano-sized magnetic particles within their cell body. In the present study, the cells of a magnetotactic bacteria M. magnetotacticum MS-1 was fractionated and the iron amount of the cell fractions were measured. In order to study the relationship between the process of the biosynthesis of magnetosome and the intracellular transport of iron, MS-1 cells were cultured under iron limited culture conditions and the amount of iron in the cell fractions were compared with those under optimal culture conditions. The whole amount of iron was measured colorimetrically. To estimate the number of ferric ion, the number of spin was determined from the ESR spectrum. The cell fractions obtained after removing magnetosome (non-magnetic fractions) contained 30-40 % of the total iron in the intact cells. There was a good correlation between the number of spin and the iron amount of non-magnetic fractions under optimal culture conditions. Under iron limited conditions, the iron amount decreased not only in the fraction containing magnetosome but also in the non-magnetic fractions. The number of spin in the soluble fraction decreased remarkably. So, the correlation between the number of spin and the amount of iron was not observed under iron limited conditions. These results imply that the ratio of ferrous ion to whole amount of iron increased in the non-magnetic fractions under iron limited conditions as compared with that under optimal conditions.

A Ferromagnetic Resonance Study of Iron Complexes as Biologically Synthesized in Magnetic Bacteria

In order to analyze the magnetic behaviors of iron complexes biologically synthesized in magnetic bacteria MS-1, we performed FMR (Ferromagnetic Resonance) measurements for each fraction of the cell. We observed FMR spectra from the ferric iron (Fe3+) compounds distributed in each fraction of the MS-1 cell. In particular, the MS fraction yielded an anisotropic FMR signal, whereas other fractions were simple FMR spectra of Gaussian type. Upon counting the numbers of spins in various cell fractions, we compared them with the iron population as determined by the 1.10-phenanthroline method. We found a good correlation between the number of spins and the iron population in several cell fractions. We concluded that the cell fractions other than those fractions containing magnetite, consist mostly of ferric irons rather than ferrous irons.

The Effect of Magnetic Field on Magnetotactic Bacteria Behaviors

The motion of magnetotactic bacteria was observed using an optical darkfield microscopy. The images were taken using video cameras, and measured by image processing techniques. In our experiment, it was found that the bacteria motion was found to follow to magnetic field frequency within some range. The observation results indicate the possibility of the bacteria behavior control by magnetic field.