Compressing a Swarm of Multicellular Magnetotactic Bacteria with an Applied Magnetic Field

Bacteria of the species Magnetoglobus multicellularis live in spherical colonies composed of 10-50 individual bacteria. The colony swims as a single unit parallel to the Earth’s magnetic field. Here we investigate the collective dynamics of a swarm of these colonies under an applied magnetic field. We orient the magnetic field towards a wall and measure the spatial distribution of the colonies. We track the motion of individual colonies as they align with the field and collide with one another and the chamber walls. We show that the distribution of colonies is the same as that of an ideal gas in a harmonic potential. We present a simple model to explain how this similarity arises and how it breaks down.