Bacterial hopping and trapping in porous media

TL;DR

This study reveals how bacterial motility in porous media involves intermittent trapping and hopping, significantly differing from traditional run-and-tumble behavior, and provides a predictive framework for long-term bacterial transport.

Contribution

It demonstrates that bacterial movement in porous media is characterized by trapping and hopping, challenging existing models and offering a new predictive understanding of bacterial migration.

Findings

Bacteria exhibit intermittent trapping and hopping in porous media.

Trapping durations and hop lengths are broadly distributed.

These factors predict long-term bacterial diffusivity.

Abstract

Diverse processes--e.g. bioremediation, biofertilization, and microbial drug delivery--rely on bacterial migration in disordered, three-dimensional (3D) porous media. However, how pore-scale confinement alters bacterial motility is unknown due to the opacity of typical 3D media. As a result, models of migration are limited and often employ ad hoc assumptions. Here we reveal that the paradigm of run-and-tumble motility is dramatically altered in a porous medium. By directly visualizing individual Escherichia coli, we find that the cells are intermittently and transiently trapped as they navigate the pore space, exhibiting diffusive behavior at long time scales. The trapping durations and the lengths of "hops" between traps are broadly distributed, reminiscent of transport in diverse other disordered systems; nevertheless, we show that these quantities can together predict the long-time bacterial translational diffusivity. Our work thus provides a revised picture of bacterial motility in complex media and yields principles for predicting cellular migration.