A simple yet reliable assay for chemotaxis in C. elegans

Animals can move towards or away from an odorant. Here we develop an assay for the nematode C. elegans that avoids use of chemical or physical immobilization when measuring response to odorants. We use opposing orientations of rectangular arenas to control for unknown gradients outside the arena and introduce a measure of dispersal to control for locomotion defects and unknown gradients within the arena, enabling the analysis of responses to a variety of chemicals. Using this setup, we found that unfed worms show reproducible movement towards the odorants butanone and benzaldehyde, and away from the odorant nonanone.