Kemotaxi

Kemotaksi, or chemotaxis, is the directed movement of a cell or organism toward or away from a chemical gradient. The term chemotaxis, coined by Wilhelm Pfeffer in 1884, describes this adaptive movement as a response to chemical signals; kemotaksi is the Turkish term used in some scientific literature.

In bacteria, chemotaxis enables navigation toward nutrients or away from harmful substances. Bacteria detect attractants and repellents through membrane-bound chemoreceptors, such as methyl-accepting chemotaxis proteins (MCPs). A signal transduction pathway, centered on the histidine kinase CheA and response regulator CheY, modulates the rotation of flagella to bias movement. Adaptation is achieved by receptor methylation and demethylation through CheR and CheB, allowing long-term gradient tracking.

In eukaryotes, chemotaxis involves G-protein-coupled receptors sensing chemoattractants such as chemokines or bacterial products. Receptor activation triggers intracellular signaling cascades (including PI3K, Rac, and Rho GTPases) that organize actin cytoskeleton remodeling and pseudopod extension toward higher concentrations. Cells such as neutrophils and Dictyostelium discoideum migrate toward infection sites or nutrient sources; chemotaxis plays roles in development, immune responses, wound healing, and cancer metastasis.

Chemotaxis is studied with assays that create stable chemical gradients, such as capillary, Boyden, and microfluidic devices, combined with live-cell imaging. Understanding chemotaxis informs fields from microbiology to immunology and oncology.