Bacterial motility in porous media: implications for environmental bioremediation strategies
While bacterial motility is well-studied on flat surfaces or in unconfined liquid media, in environment and energy applications, most bacteria are found in disordered porous media, such as soils, sediments, and subsurface formations. Understanding how porous confinement alters bacterial motility is therefore critical to processes ranging from fouling of oil reservoirs, sustaining plant growth, and remediating contaminants in soil. To address these problems, we have designed transparent porous media that enable direct visualization of bacteria in situ. Using this platform, first, we interrogate the migration of E. coli bacteria through the 3D pore space. Direct visualization enables us to reveal a new mode of hopping and trapping motility exhibited by individual cells, in stark contrast to the paradigm of run-and-tumble motility, in which cells are intermittently and transiently trapped as they navigate the pore space. Further, analysis of these hopping and trapping dynamics enables prediction of single-cell transport over large length and time scales. Second, we use 3D bioprinting to embed dense colonies of E. coli inside porous medium and investigate how bacterial hopping and trapping motility manifests in multicellular communities. 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. Finally, we focus on design strategies of synthetic porous media which enable us to bioprint and grow precisely structured bacterial biofilms—a powerful tool to create artificial biofilms for water remediation. Together, these studies highlight how this transparent porous medium provides a powerful platform to design and interrogate bacterial communities at their natural habitat—with implications for bioremediation and purifying contaminated water.