A Method for Measuring the Motility of Bacteria and for Comparing Random and Non-random Motility

Abstract

SUMMARY The motility of Escherichia coli was measured in capillary tubes by deter- mining the distribution of bacteria throughout the tube (the complete assay) or simply by locating the point of furthest advance of the bacteria-the frontier of the migration (the frontier assay). The diffusion of 14C-glucose was similarly measured in capillary tubes by determining the distribution of radioactivity throughout the tube. The diffusion of glucose under the condi- tions used was correctly described by the known diffusion equation.The method gives a measure of the net forward velocity of the bacteria. Interpretations, advantages and disadvantages of these assays are given. The method also gives a measure of the degree of randomness of the motility. When chemotaxis is taking place, a very high proportion of the bacteria leave the origin and migrate as a band. When bands are not allowed to form, by omitting methionine, the motility of the bacteria qualitatively resembled a random process, such as the diffusion of glucose.