chemotaktische

Chemotaxis is the directed movement of a cell or organism in response to a chemical gradient. It describes how a cell biases its movement toward higher concentrations of a chemoattractant (positive chemotaxis) or away from a chemical cue (negative chemotaxis). By contrast, chemokinesis refers to changes in the rate or pattern of movement that are not directionally oriented by a gradient. In German-language literature the adjective chemotaktische is commonly used to describe chemotaxis-related phenomena.

In bacteria, chemotaxis is mediated by chemoreceptors that detect environmental chemicals and transmit signals to a flagellar motor. In Escherichia coli, methyl-accepting chemotaxis proteins (MCPs) feed into a two-component system (CheA, CheY) that modulates motor rotation, balancing runs and tumbles to steer toward attractants. Adaptation to persistent stimuli occurs through receptor methylation and demethylation (CheR, CheB), maintaining sensitivity across changing conditions.

In eukaryotes, chemoattractants are often detected by G protein-coupled receptors or receptor tyrosine kinases. Cells polarize at the leading edge, with signaling cascades that involve phosphoinositide 3-kinase (PI3K), PIP3 accumulation, and the activation of Rho family GTPases such as Rac and Cdc42, driving actin polymerization and membrane protrusion in the gradient direction. Signaling is integrated with adhesion and mechanical cues to produce persistent migration.

Examples include the social amoeba Dictyostelium discoideum, which aggregates in response to cAMP, and mammalian immune cells like neutrophils guided by chemokines (e.g., IL-8) and complement factors. Chemotaxis also shapes processes in development, wound healing, and cancer metastasis.

Measurement approaches include Boyden chambers, under-agarose assays, and microfluidic devices that create and maintain chemical gradients for real-time observation.