Chemotaksi

Chemotaksi, also known as chemotaxis, is the movement of an organism or cell in response to a chemical gradient, typically toward higher concentrations of a nutrient or away from a toxin. It occurs in bacteria and archaea, as well as in many eukaryotic cells such as neutrophils and Dictyostelium discoideum, and it plays a critical role in development, immunity, and infection.

In bacteria such as Escherichia coli, chemotaksi is mediated by chemoreceptors that detect attractants or repellents. These receptors modulate the activity of the histidine kinase CheA via the linker protein CheW. The CheA kinase controls the phosphorylation state of CheY, which binds the flagellar motor to induce clockwise or counterclockwise rotation, altering swimming behavior. Adaptation occurs through reversible methylation and demethylation of receptors by CheR and CheB, enabling sensitivity to persistent gradients.

In eukaryotes, chemotaksi involves receptors such as G protein–coupled receptors or receptor tyrosine kinases that sense chemoattractants and trigger signaling cascades, including PI3K and RAC/CDC42–dependent actin remodeling. Cells polarize, extend protrusions, and migrate directionally along gradients. They can use local contraction and adhesion to move through tissues.

Chemotaksi can be positive (toward attractants) or negative (away from repellents). Studies often employ microfluidic devices and mathematical models, such as the Keller–Segel framework, to describe gradient sensing and collective migration in populations.

Significance includes roles in bacterial colonization, immune cell trafficking, wound healing, and cancer metastasis. Advances in understanding chemotaksi inform areas from infectious disease to bioengineering and therapeutic development.