Quasi-elastic light scattering from migrating chemotactic bands of Escherichia coli. III. Studies of band formation propagation and motility in oxygen and serine substrates.

A series of light scattering experiments have been performed to study both macroscopic aspects of band formation and propagation and microscopic motility parameters of Escherichia coli in the combined substrate gradients of oxygen and serine. From the band formation experiment the conclusion is drawn that a minimum threshold gradient of the substrate is required for bacteria to form a band. From the band propagation experiment in the serine substrate the motility coefficient mu and chemotactic coefficient delta are determined. A separate quasi-elastic scattering experiment has been made with a propagating band to obtain three microscopic motility parameters: mean twiddle time tau 1, mean run time tau 2, and mean run speed V2. Finally, a scaling argument is made to connect the macroscopic parameters mu and delta with the microscopic parameters tau 1, tau 2, and V2, thus achieving a unified understanding of macroscopic and microscopic aspect of chemotaxis.