Worm Breeder's Gazette 13(5): 44 (February 1, 1995)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Genetics, University of Washington, Seattle, WA 98195
In an effort to elucidate the behavioral mechanism governing the chemotaxis response in C. elegans, we performed and analyzed the results from a series of single-animal chemotaxis assays. We hypothesized that the movement toward attractants by C. elegans might include a component analogous to the "run and tumble" phenomenon that occurs in bacteria in response to chemical attractants. This response is characterized by the suppression of tumbles (reorientation movements), in favor of runs (continuous movement in one direction), when a bacterium is traveling up an attractive chemical gradient. C. elegans has movements that are somewhat analogous: continuous forward movement (runs) occasionally interrupted by bouts of backing and reorienting (tumbles). Based on our hypothesis, we predicted that the length of each nematode run would increase if the animal were traveling up an attractive gradient, and that the frequency of tumbles would increase if the animal were traveling down an attractive gradient. In order to assay chemotaxis behavior, we followed an experimental protocol similar to that devised by Bargmann et al. I, except that we directly recorded movement of one animal in an assay. We performed two types of assays: those with 7 microL of isoamyl alcohol as attractant, and those without attractant. We used keystrokes interpreted by a computer program to record such qualities as direction of movement, times and lengths of tumble bouts and runs, speed of movement, etc. After running a series of both types of assays, all data were compiled, and the run lengths and tumble frequencies that occurred in the absence of attractant and in the presence of attractant when moving up or down the attractive gradient were compared. Contrary to our hypothesis, our data indicate that run length does not seem to be affected by the presence or absence of attractant or orientation of movement on the gradient. Additionally, preliminary evidence suggests that the animals' initial choice of direction following reorientation was not strongly biased by the gradient of attractant. We conclude that the chemotaxis response to this odorant by C. elegans does not include a significant component analogous to the run and tumble response in bacteria. We infer that another type of orientation mechanism must control the response to attractant. We posit that this alternate mechanism is one that allows the animal to adjust its direction of movement while running based on information about the gradient. Bargmann, C. I., Hartweig, E.. and Horvitz, H. R., Cell 74: 515-527, 1993