Run-and-tumble motility enables equatorial magnetoaerotaxis

Guided by Earth’s magnetic field, magnetotactic bacteria (MTB) seek out microoxic environments in the sediments of swamps, lakes, and oceans for survival. To accomplish this, MTB synthesize magnetic nanoparticles that mechanically orient the cells along Earth’s magnetic field, which is mostly parallel to the water column over a broad range of latitudes. In the current paradigm, magnetotaxis provides a global orientation for the cells and facilitates a one-dimensional aerotactic search along naturally occurring, parallel oxygen gradients through ‘run-and-reverse’ motility. However, a variety of MTB species thrive at the equator, in spite of the orthogonal magnetic field and oxygen gradients. Using a microfluidic device and Helmholtz coil, we independently control an oxygen gradient and an orthogonal magnetic field, enabling precise measurements of MTB motility under equatorial conditions. 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. These results establish a new survival mechanism for equatorial magnetoaerotaxis in bacteria.