Trait-specific dispersal of bacteria in heterogeneous porous media

Abstract:

Dispersal of organisms determines the fate of individuals and communities, and can regulate ecosystem functioning. Predicting dispersal patterns across scale is important to understand microbial life in heterogeneous porous media as soils and sedimentary environments.

We investigated the flow-driven dispersal of motile and non-motile bacteria in hydrated porous media mimicked by microfluidic devices. By combining information at different scales, that is from pore-scale to macro-scale, we tracked individual bacterial trajectories and measured the overall breakthrough curves and bacterial deposition profiles. We provide a solid link between our microscopic and macroscopic observations developing a stochastic model that takes explicitly into account the physical heterogeneity and transport dynamics within a Continuous Time Random Walk (CTRW) framework.

We show that motile cells of Pseudomonas putida evaded flow-imposed trajectories, enabling them to explore larger pore areas than non-motile cells. Additionally, cells exhibited a rotation as a result of hydrodynamic torque imparted by the local shear. Motile cells were less susceptible to the torque, maintaining their body oriented towards flow direction, this affected the velocity distribution of the motile population and thus the overall transport properties.

Our findings highlight how macro-scale dispersal patterns result from the coupling between transport and motility mechanisms occurring at the pore scale. It also emphasizes how micro-scale flow heterogeneity, perceivable by individual cell, may have very contrasting impacts on bacteria exhibiting different phenotypic traits. Our findings suggest that motility coupled with heterogeneous flows can be beneficial to bacteria in confined environments as it enables them to actively explore space for resources or evade from regions with unfavorable conditions.