RANDOM MOTILITY OF SWIMMING BACTERIA - SINGLE CELLS COMPARED TO CELL-POPULATIONS

The motility of a population of swimming bacteria can be characterized by a random motility coefficient, mu, the operational equivalent of a diffusion coefficient at the macroscopic level and in the absence of interacting chemical gradients. At the microscopic level, random motil ity is related to the single-cell parameters: speed, tumbling probabil ity, and index of directional persistence (related to the angle a cell 's path assumes following a change in direction). Various mathematical models have been proposed for relating the macroscopic random motilit y coefficient to these microscopic single-cell parameters. In separate experiments, we have measured motility at both the cell-population an d single-cell levels for Escherichia coli. The agreement of these resu lts shows that the macroscopic transport behavior of a population of m otile bacteria can be predicted from straightforward microscopic obser vations on single cells.