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

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 <i>χ</i>_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 <i>Pseudomonas putida</i>. This work demonstrated a framework that integrates experimental and modeling approaches at both population and individual scales to investigate mechanisms underlying bacterial transport phenomena.