Trapping in porous microstructure suppresses magnetotactic bacterial transport

Swimming magnetotactic bacteria thrive in porous sediments of marine environments, which they navigate by orienting relative to Earth’s magnetic field. While their motility is well-studied in bulk media, the physical mechanisms regulating magnetotactic bacterial motility in porous environments are not clear. Using microfluidic experiments complemented by Langevin simulations, we investigate the effect of porous microstructure and the role of disorder in dictating cell transport. Cell-surface scattering from solid boundaries provides an effective cell reorientation mechanism that yields diffusive, random walks in the absence of a magnetic field for both ordered and disordered media. In the presence of a strong magnetic field, cell alignment leads to ballistic transport and enhanced cell propagation in an ordered lattice of obstacles. However, trapping in concave pore geometries significantly hinders their mobility in disordered media. Combined with the known weak cell alignment to Earth’s ambient magnetic field, our findings suggest that cell-surface scattering may provide an escape mechanism to help avoid trapping, while still facilitating cell dispersal in naturally disordered porous geometries.