Collective migration of bacteria in disordered media

While bacterial motility is well-studied on flat surfaces or in unconfined liquid media, most bacteria are found in disordered porous media, such as biological gels and tissues, soils, sediments, and subsurface formations. Understanding how porous confinement alters bacterial motility is therefore critical to modeling the progression of infections, applying beneficial bacteria for drug delivery, and bioremediation. We recently discovered that isolated cells of E. coli move through disordered media via intermittent hopping and trapping, reminiscent of thermally-activated transport. Here, we use direct visualization and 3D bioprinting to investigate how this behavior manifests in multicellular communities in porous media. We find that cellular chemotaxis drives collective migration—and that this process depends sensitively on pore-scale confinement, colony density, and differential metabolism of nutrients. Our results thus expand the current understanding of collective migration, which focuses on populations in homogeneous environments, to the case of bacteria in disordered porous media.