Confinement and activity regulate bacterial motion in porous media

TL;DR

This study reveals how pore-scale confinement and bacterial activity influence E. coli motility in porous media, highlighting a new hopping-and-trapping behavior and providing insights for modeling bacterial movement in complex environments.

Contribution

It uncovers the dependence of bacterial hopping and trapping on confinement and activity, introducing an entropic trapping model for motility in porous media.

Findings

Hopping is determined by pore-scale confinement, independent of activity.

Trapping depends on the interplay between confinement and activity.

Results support an entropic trapping model for bacterial motility.

Abstract

Understanding how bacteria move in porous media is critical to applications in healthcare, agriculture, environmental remediation, and chemical sensing. Recent work has demonstrated that E. coli, which moves by run-and-tumble dynamics in a homogeneous medium, exhibits a new form of motility when confined in a disordered porous medium: hopping-and-trapping motility, in which cells perform rapid, directed hops punctuated by intervals of slow, undirected trapping. Here, we use direct visualization to shed light on how these processes depend on pore-scale confinement and cellular activity. We find that hopping is determined by pore-scale confinement, and is independent of cellular activity; by contrast, trapping is determined by the competition between pore-scale confinement and cellular activity, as predicted by an entropic trapping model. These results thus help to elucidate the factors that regulate bacterial motion in porous media, and could help aid the development of new models of motility in heterogeneous environments.