Quasielastic light scattering from migrating chemotactic bands of Escherichia coli. II. Analysis of anisotropic bacterial motions.

Chemotactic effects of dissolved oxygen on motions of Escherichia coli in a motility buffer solution have been studied by measurements of quasielastic light scattering. Under conditions where the bacteria form a sharp band in an oxygen concentrations gradient created by their metabolism, components of motions along the direction of the gradient and perpendicular to it were studied separately at each point within the band profile. A theoretical model for bacterial self correlation function based on two-state motions has been developed to extract the mean square speed of run motion and the relative probability of twiddle vs. run at each point of the band profile. A combined novel experimental set-up and new data analysis method allowed us to extract also the mean square displacements at short times along and perpendicular to the direction of the gradient. Parameters extracted from the measured correlation functions have been discussed in the framework of the established picture of bacterial motions under chemotaxis.