A Simple, Quantitative Method for Measuring Chemotaxis and Motility in Bacteria

The response of bacteria to chemical changes in their environment has been much studied recently (for reviews. see Adler, 1976, and Berg, 1975). The method of choice for quantitatively measuring chemotaxis has been an adaptation by Adler (1969) of a method used at the turn of the century by Pfeffer (1888), which measures, by viable plate counts, the number of bacteria moving into a capillary under a chemotactic stimulus. This method is slow, needing overnight incubation of the plated bacteria. Here we describe a method which can be used to measure positive and negative chemotaxis in bacteria quickly and accurately. The method uses a Coulter counter to measure the percentage of a suspension of motile bacteria passing through a polycarbonate membrane in a given time, into a cell-free buffer, under a chemotactic influence. This method can also be adapted for measuring the percentage of motile bacteria in a culture. This is achieved by comparing the number of bacteria passing through the membrane in a given time with standards of known percentage motility.