Chemotaksis

Chemotaksis, or chemotaxis, is the directed movement of a cell or organism in response to a chemical gradient. It is a fundamental mechanism by which single cells (such as bacteria, amoebae, and immune cells) and multicellular tissues coordinate migration during development, immune responses, wound healing, and infection. Movement is guided by attractants that elicit positive chemotaxis or repellents that cause negative chemotaxis; the strength and profile of the gradient influence direction and speed.

In bacteria, chemotaxis enables navigation toward nutrients or away from harmful substances. The process uses chemoreceptors, such as methyl-accepting chemotaxis proteins (MCPs), to sense chemical cues and modulate the activity of a two-component signaling system (CheA) that controls the flagellar motor. The phosphorylation state of CheY biases flagellar rotation to produce longer runs or more frequent tumbling, aligning movement with the gradient. Adaptation is achieved through reversible receptor methylation (CheR and CheB).

In eukaryotic cells, chemotaxis involves more complex signaling networks that coordinate polarized movement. Receptors—often G protein-coupled receptors or receptor tyrosine kinases—detect gradients and trigger localized signaling at the leading edge. Downstream pathways regulate actin dynamics through Rho family GTPases and phosphoinositide signaling (for example, PI3K and PIP3), coordinating protrusion, adhesion, and retraction to steer toward the attractant.

Experimental study of chemotaxis employs assays and microfluidic devices that create stable chemical gradients to analyze cell behavior. Dysregulation of chemotaxis is implicated in inflammatory diseases and cancer metastasis, while proper chemotaxis is essential for host defense, development, and tissue repair.