Heat Production by Bacterial Magnetosomes Exposed to an Oscillating Magnetic Field

In this work, we examined mechanisms of heat production by whole intact cells of the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1, as well as by their extracted chains of magnetosomes or extracted individual magnetosomes when exposed to an oscillating magnetic field of frequency 108 kHz and field amplitudes 23 and 88 mT. In this study, magnetosomes did not contain magnetite as the magnetite oxidized to maghemite. For intact bacterial cells that contain chains of magnetosomes, heat is generated through hysteresis losses, yielding specific absorption rates (SARs) of 115 +/- 12 W/g(Fe) at 23 mT and 864 +/- 9 W/g(Fe) at 88 mT. When the chains of magnetosomes are extracted from the bacterial cells and exposed to the same magnetic field, the heat-producing mechanism includes an additional contribution that is due to their rotation in the magnetic field. This contribution appeared to result in higher observed SARs of 864 +/- 13 W/g(Fe) at 23 mT and 1242 +/- 24 W/g(Fe) at 88 mT. SAR values of 529 +/- 14 W/g(Fe) at 23 mT and 950 +/- 18 W/g(Fe) at 88 mT were obtained with individual magnetosomes whose membranes had been removed.