Aligning Paramecium caudatum with static magnetic fields

¹ Brown University

^* To whom correspondence should be addressed. E-mail: guevorkian{at}physics.brown.edu.

Submitted on July 29, 2005
Revised on October 13, 2005
Accepted on 10 January 2006

	Abstract

As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth's magnetic field (5x10^-5 T) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align with intense static magnetic fields greater than 3 Tesla. Otherwise straight trajectories curve in magnetic fields and eventually orient parallel or anti-parallel to the applied field direction. Neutrally buoyant immobilized paramecia also align with their long axis in the direction of the field. We model this magneto-orientation as a strictly passive, non physiological, response to a magnetic torque exerted on the diamagnetically anisotropic components of the paramecia. We have determined the average net anisotropy of the diamagnetic susceptibility, _p, of a whole Paramecium:_p=(6.7±0.7)x10^-23 m³. We show how the measured, _p compares to the anisotropy of the diamagnetic susceptibilities of the components in the cell. We suggest that magnetic fields can be exploited as a novel, non-invasive, quantitative means to manipulate swimming populations of unicellular organisms.

Key Words: cell manipulation, diamagnetic, microorganism, swimming, torque, unicellular