Brown University Group Develops Magnetic Force Technique to Invert the Buoyancy of Gravity-Sensitive Organisms

James Valles' group in the Brown University physics department has established a method for manipulating the buoyancy of swimming protists (microscopic organisms) using the magnetic forces produced by a superconducting solenoid. With this novel tool, their goal is to investigate the fundamental interactions between gravity forces (in this case, buoyancy) and biological systems.

Complex biological systems such as human beings and even single-cell organisms respond to the force of gravity. The protist paramecium, for example, adjusts its swimming propulsion in response to changes in its orientation and the density of its surrounding medium. While such sensitivities have been known for some time, the mechanisms through which gravity exerts its influence are not established. Karine Guevorkian, a Brown graduate student, and Professor Valles have developed a magnetic force technique that is suitable for investigating how organisms sense gravity. In their experiments, they immerse paramecium in its medium in the non-uniform magnetic field region of a superconducting solenoid. The magnetic field exerts magnetic forces on both the paramecium and their surrounding medium. By adjusting the strength of the magnetic field and the magnetic susceptibility of the medium, they have made non-swimming paramecium, which sediment under normal conditions, sediment faster, attain neutral buoyancy, or even rise. The latter corresponds to effectively inverting gravity for the paramecium. The Brown group is currently investigating the swimming behavior of paramecium under these various simulated gravity environments to probe its gravity-sensitivity. This method can be further expanded for the study of other cell systems and the response of various soft condensed matter to novel force environments.