Magnetotactic bacterial scattering in porous media hinders transport

Swimming cells exhibit complex surface scattering behaviors in both natural and engineered porous habitats, impairing their persistent random walks. Using microfluidics experiments complemented with Langevin simulations, we study how the scattering of magnetotactic bacteria (MTB) within a lattice of obstacles modifies cell transport, and how guidance by an external field augments their mobility. MTBs are used as a model biological system, because they share motility mechanisms with many other bacterial species, and their swimming direction is easily manipulated via an external magnetic field. We show that both the diffusive and directed mobility of the cells decreases markedly in the presence of porous microstructure compared to bulk fluid. Moreover, the spacing between the obstacles and the degree of the disorder in the lattice play a key role in the magnitude of the observed reduced mobility. These results are an important step toward understanding the physical ecology of swimming cells in quiescent porous media as well as for controlling micro-robots in complex environments.