Estimation of chemotaxis intensity of Salmonella cells by the capillary assay and biased random walk simulation

Bacterial cells exhibit chemotaxis by repeating a straight swimming (run) and an abrupt change of the swimming direction (tumble). Cells detect the change in the concentration of a chemical attractant during the run and decrease the frequency of the tumbles if the cells have swum toward the favorable direction. As for the chemotaxis mechanism, a mathematical model has been proposed where the frequency of the tumble is correlated with the chemotaxis intensity. In this study, we observe the chemotactic behaviors of bacterial cells and compare the measurement with the mathematical model to quantify the chemotaxis intensity.