A magnetotactic bacterium capable of magnetic sensing.

Magnetosensitive organisms have the ability to sense and respond actively to features of magnetic fields such as the direction or magnitude. Until now, magnetosensing has been characterized primarily in higher organisms, involving either a cryptochrome-based mechanism or direct magnetic interactions with magnetic particles. Magnetotactic bacteria, microorganisms forming intracellular chains of magnetic nanoparticles, are thought to only passively orient along field lines. In this study, we reveal that the cultivated magnetotactic bacterium SS-5 also exhibits magnetosensing. The microorganisms indeed swim faster in a physiological magnetic field compared to when the field is canceled. This speed difference is independent of illumination wavelength but is altered when the bacterial magnetic backbone is disrupted. We thus propose that magnetosensing in the bacteria originates from a magnetomechanical signal transduction along the magnetotactic filament. Our findings also show that this response depends on relative changes in magnetic field intensity, akin to the Weber-Fechner laws, suggesting that magnetosensing operates similarly to other forms of taxes.