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 constant sensing and 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. We further show that when toxic organic contaminants are present, salt gradients enhance bacterial dispersion toward them, demonstrating improved chemotactic transport. This work uncovers a previously unrecognized mechanism by which salt gradients direct bacterial motility, revealing a physical route to control microbial transport and colonization in complex environments.