Pseudomonas putida Chemotactic Efficiency toward Naphthalene at a NAPL–Water Interface Decreased under Increasing Shear Flow

TL;DR

This study shows how fluid flow affects the movement of bacteria toward pollutants, which is important for cleaning up contaminated groundwater.

Contribution

The paper introduces a framework combining experiments and modeling to quantify how shear flow impacts bacterial chemotactic efficiency.

Findings

Bacteria near NAPL interfaces were retained more at low fluid velocities.

Higher flow velocities reduced chemotactic sensitivity and population density near the interface.

Bacterial motion aligned more with flow direction as velocity increased.

Abstract

Chemotactic bacteria have the potential to enhance the
bioremediation
of nonaqueous phase liquid (NAPL) pollutants by preferentially migrating
toward contaminant sources. Although groundwater flow has been shown
to influence bacterial chemotaxis, its quantitative influence on intrinsic
motility parameters governing chemotactic strategies remains unresolved.
Using a T-shaped microfluidic device, mimicking a NAPL droplet trapped
within a pore throat, we show that chemotactic bacteria exhibited
greater retention near the NAPL interface at low fluid velocities
(0.5 m/d and 1 m/d; corresponding wall shear rates of 0.58 and 1.16
s–1, respectively), while both population density
and accumulating area declined at higher velocities. Continuum-level
simulations of bacterial transport indicated a reduction in the chemotactic
sensitivity coefficient χ
o by an
order of magnitude at flow velocities above 5 m/d (5.78 s–1). Trajectory analysis of bacteria from videomicroscopy revealed
increasing alignment of bacterial motion with the flow direction as
the fluid velocity increased. We conducted agent-based model simulations
to further demonstrate that flow-induced suppression of reversal frequency
reduced chemotactic efficiency in Pseudomonas putida. This work demonstrated a framework that integrates experimental
and modeling approaches at both population and individual scales to
investigate mechanisms underlying bacterial transport phenomena.

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