A System for Analysing the Motion of Individual Micro-Organisms

Abstract

Individual motile bacteria, e.g. E. coli, are known to execute a random walk, very similar in appearance to Brownian motion but on a larger scale. Now if all the bacteria of a particular strain were identical (i.e. had the same average speed and travelled the same average distance between changes of direction) then some of the properties of the individual bacterium could be deduced from the observation of an assembly of bacteria; for example, measuring the diffusion (motility) coefficient would yield the product of the velocity and mean distance travelled between changes of direction and vice versa. However, it appears from the results of Adler and Dahl¹ that bacteria are not identical so that the dispersion of an assembly of bacteria does not obey the classical diffusion equation. A method of calculating the dispersion of a heterogeneous assembly of motile micro-organisms has been given by Thonemann and Evans² and compared with the results of Adler and Dahl.