Rapid chemotaxis assay using radioactively labeled bacterial cells

A rapid chemotaxis assay is described in which radioactively labeled cells of the assay organism are used to detect the number of cells trapped in capillaries containing attractant. The sensitivity and reproducibility of the radioactive technique is comparable to that of the dilution plating procedure of Adler (J. Adler, J. Gen. Microbiol. 17:77-91, 1973), but is faster and also permits the results of the assay to be determined on the day that the assay is run. The method could be particularly useful for environmental studies and for field experiments, since it does not rely on sterile techniques for dilution plating.