Stochastic dynamics of magnetosomes and a mechanism of biological orientation in the geomagnetic field.

The rotations of nanoscopic magnetic particles, magnetosomes, embedded into the cytoskeleton are considered. Under the influence of thermal disturbances, a great number of magnetosomes are shown to move chaotically between two stable equilibrium positions, in which their magnetic moments are neither parallel nor antiparallel to the static Earth's magnetic field (MF). The random rotations attain the value of order of a radian. The rate of the transitions and the probability of magnetosomes to be in the different states depend on the MF direction with respect to an averaged magnetosome's orientation. This effect explains the ability of migratory animals to orient themselves faultlessly in long term passages in the absence of the direct visibility of optical reference points. The sensitivity to deviation from an "ideal" orientation is estimated to be 2-4 degrees. Possible involvement of the stochastic dynamics of magnetosomes in biological magnetic navigation is discussed.