Description
Magnetotactic bacteria navigate redox gradients through magnetoaerotaxis—passive magnetic alignment coupled with active aerotactic swimming toward optimal oxygen levels. The consensus model, based on run-reverse motility in model species like AMB-1/MSR-1, assumes bacteria reduce 3D search to 1D by swimming along magnetic field lines. However, this framework (i) does not account for the diverse swimming behaviors across MTB phyla, including the run-tumble and complex helical trajectories of species like the bilophotrichous Magnetococcus marinus MC-1 (ii) does not explain the presence of MTB at the equator.
To understand how morphology and motility couple with magneto-aerotaxis across latitudes, we compared MC-1 and AMB-1 under three geomagnetic conditions using 3D Helmholtz coils and microfluidics: magnetic field parallel and antiparallel (poles), and perpendicular (equator) to oxygen gradients. Surprisingly, MC-1 departs from field-aligned swimming when gradients are perpendicular to the magnetic field, exhibiting run-tumbles and misaligned reversals that enable spatial exploration orthogonal to the magnetic field. This allows MC-1 to migrate along oxygen gradients even when strong perpendicular magnetic fields are applied, as demonstrated during dynamic gradient switching. In contrast, AMB-1 maintains mostly run-reverse behavior and struggles with perpendicular migration.
These results explain why coccoid MTB like MC-1 dominate at the geomagnetic equator, where magnetic fields are perpendicular to oxygen gradients—a scenario where traditional, unidimensional magneto-aerotaxis would be disadvantageous. Our findings demonstrate that MC-1 adaptively varies its swimming strategy to navigate complex environmental geometries, highlighting the importance of species-specific motility in understanding MTB ecology and distribution.