Equatorial Magnetoaerotaxis of Swimming Bacteria

Magnetotactic bacteria (MTB) synthesize magnetite nano-particles attached to the cell membrane, which mechanically orient the swimming cells parallel to Earth’s magnetic field. The accepted paradigm is that, at a broad range of latitudes, the magnetic field is nearly perpendicular to the surface of the Earth, whereby ‘run-and-reverse’ motility along the magnetic field enables efficient aerotaxis in the water columns of swamps, lakes, and oceans. However, at the equator, in spite of the magnetic field being orthogonal to naturally occurring oxygen gradients, a variety of MTB species are found to thrive there. Using a microfluidic device and Helmholtz coils, we generate and independently control an oxygen gradient and an orthogonal magnetic field, enabling precise measurements of MTB motility. In contrast to the current paradigm, we show that Magnetococcus marinus (MC-1) achieves ‘run-and-tumble’ motility, which facilitates exploration and aerotaxis perpendicular to the magnetic field, establishing a new survival mechanism for equatorial magnetoaerotaxis.