diffusiotactic

Diffusiotaxis is a form of taxis in which cells or motile particles migrate in response to a gradient of a diffusing chemical substance. The gradient typically arises from diffusion of a solute from a localized source, creating spatial variation in concentration that organisms can sense and use to direct movement. Positive diffusiotaxis refers to movement toward higher concentrations, while negative diffusiotaxis describes movement away from them.

Mechanistically, diffusiotaxis involves sensing local chemical concentration through receptors or signaling pathways and translating that information into directed motility. Depending on the organism, this can influence flagellar rotation, run-and-tumble behavior in bacteria, or the extension of pseudopods in amoeboid cells. The precise molecular components vary with the species and solute. Diffusiotaxis is closely related to chemotaxis, but the distinction lies in the emphasis on gradients that are generated by diffusion rather than externally imposed, static gradients. In some contexts the same sensory and signaling machinery can mediate both phenomena. Diffusiotaxis is also related to diffusiophoresis, a physical transport mechanism where solute gradients move colloidal particles without biological sensing.

Applications and relevance include understanding microbial foraging strategies, biofilm formation, and the behavior of synthetic active matter designed to respond to chemical cues. Studying diffusiotaxis helps illuminate how organisms exploit transient, diffusion-shaped chemical landscapes in natural environments, such as nutrient plumes or decaying matter.

Terminology usage varies in the literature, and some authors describe diffusion-driven gradients under different labels. Nevertheless, diffusiotaxis provides a useful framework for describing movement guided by diffusion-created chemical gradients across diverse biological and synthetic systems.