This is another way to visualize the turning of cells in a magnetic field. The light scattering properties of a bacterial culture (specifically of bacteria that are asymmetric in shape) will differ based on the orientation of the cells relative to a light source. When a magnet is placed parallel to a tube, bacteria are aligned such that light passes through their cellular short axis. In this orientation a magnetic culture will scatter less light than when the cells are aligned perpendicular to the light. For nonmagnetic bacteria, there is no preferred orientation and thus the same level of light scattering is observed. In this video, the culture on the left is grown with iron and the one on the right is grown without iron. Notice that the culture on the left becomes cloudier when the magnet is perpendicular to the tube. By applying the same principle to a spectrophotometer we can quantitate the magnetic response of a culture, a measurement that is known as Cmag.
Video: Arash Komeili, Hand model: Dr. Dorothee Murat.