Experimental studies and mathematical modeling are reported for the chemotactic response of E. coli to a combination of attractant (methylaspartate) and repellent (nickel ion) concentration gradients. Methylaspartate and nickel ion interact with the same membrane-bound receptor to initiate the sequence of events that modulates the tumbling frequency of the swimming bacteria. The random motility and the chemotactic sensitivity coefficients, transport parameters used to characterize the migration of bacterial populations, were determined from experimental assays for each chemoeffector separately and then in combination. We developed a simple model to describe the initial binding step of the attractant and repellent and the first step in the intracellular signal transduction mechanism while treating the reminder of the biochemical pathway as a "black box". Our signal integration model naturally identifies nickel ion as a repellent, is capable of describing quantitatively the response to the individual attractant and repellent and predicts the correct qualitative behavior for the combined response.

Joint work with Peter T. Cummings

Back to Workshop Schedule

1998-1999 Mathematics in Biology