Stabilizing by steering: Enhancing bacterial motility by non-uniform diffusiophoresis
Bacteria often traverse confined spaces to perform critical functions in symbiosis, infection, drug delivery, and soil bioremediation. While the canonical run-and-tumble strategy enables exploration, its reliance on stochastic reorientation limits efficiency under confinement. We show that salt gradients can physically steer Pseudomonas putida by biasing their runs toward salt through asymmetric diffusiophoretic forces. These gradients impose a torque strong enough to overcome Brownian rotation, aligning cells along the gradient and producing straighter, more persistent motion. This response persists in a Δ{cheA} mutant, demonstrating that canonical CheA-dependent chemotaxis is not required. We further show that when toxic organic contaminants are present, salt gradients promote bacterial dispersion toward the source despite reduced motility, suggesting potential applications in bacterial delivery for bioremediation. This work uncovers a previously unrecognized mechanism by which salt gradients direct bacterial motility, revealing a physical route to control microbial transport in complex environments.