Extremely low-frequency magnetic fields affect the movement of magnetotactic cocci

Abstract

Magnetotactic bacteria are microorganisms that swim following the geomagnetic field lines, because of an intracellular magnetic moment that aligns their body to the magnetic field lines. For that reason, these bacteria are appropriate for the study of microorganisms’ motion. The present paper studies the swimming trajectories of uncultured magnetotactic cocci under the effect of combined constant (DC) and alternating (AC) magnetic fields oscillating at frequencies that formally correspond to the cyclotron frequency for Ca²⁺, K⁺, Fe²⁺ and Fe³⁺ ions. The swimming trajectories were observed to be cylindrical helixes and their helix radiuses, frequencies, axial velocities and orientation angles of the trajectories relative to the constant magnetic field were determined. The orientation angles were used to calculate the magnetic to thermal energy ratio, which helps the study of the disorientating effect of the flagellar motion. Our results show that combined magnetic fields tuned to the resonance of Ca²⁺ ions affect all the trajectory parameters. Frequencies associated to Ca²⁺ and K⁺ do not affect the bacterial swimming direction relative to the magnetic field direction. On the other hand, frequencies associated to Fe²⁺ and Fe³⁺ do change the bacterial swimming direction relative to the magnetic field direction, which means that those frequencies affect the flagellar function. These results show indirect evidence of the action of calcium binding proteins in the motility of magnetotactic cocci.

Keywords:

magnetotaxis, magnetotactic cocci, ion parametric resonance model, ion cyclotron resonance model, calcium-binding proteins, sheath-associated protein