chemotactic

Chemotactic describes the ability of cells or organisms to move in response to chemical gradients. It refers to a directed, purposeful movement toward higher concentrations of a chemical (positive chemotaxis) or away from it (negative chemotaxis). The term is used across biology to describe processes that involve sensing a chemical cue and repositioning motility machinery accordingly.

In bacteria, chemotaxis is well characterized and involves chemoreceptors, such as methyl-accepting chemotaxis proteins (MCPs), that detect attractants or repellents. These receptors influence a two-component signaling system (CheA and CheY) that modulates the rotation of the flagellar motor. Attractants tend to promote longer runs with fewer tumbles, while repellents increase tumbling. Adaptation to persistent signals is achieved through receptor methylation and demethylation by CheR and CheB, allowing the system to reset sensitivity.

In eukaryotes, chemotaxis relies on more complex signaling networks. Receptors such as G protein–coupled receptors or receptor tyrosine kinases detect chemoattractants like IL-8, C5a, formyl peptides, or cAMP. Localized signaling, often involving PI3K, PTEN, and small GTPases like Rac and Cdc42, creates a leading-edge actin fold that forms protrusions, while the cell body retracts the rear. Model organisms include Dictyostelium discoideum and human immune cells such as neutrophils and macrophages.

Chemotaxis plays a critical role in physiology, including immune cell trafficking, wound healing, and development. Dysregulated chemotaxis is associated with inflammatory diseases and cancer metastasis. Researchers study gradients, receptor sensitivity, and noise to understand the efficiency and limits of chemotactic movement.