Tuesday, September 18, 2012
101 Stanley Thomas Hall
Tulane University (Uptown)
Refreshments will be served
Julie Simons, Tulane University, Center for Computational Science
The Volcano Effect in Bacterial Chemotaxis
Chemotaxis is the directed motion towards a chemical attractant. Bacteria tend to move in a swim/tumble process, increasing their swimming time if the environment is improving in the current direction, and randomly reorienting during the tumbling phase. At a macroscopic level, this biased random walk has been modeled by the Keller-Segel (K-S) equations which are conservation laws that have a bacterial flux biased in the direction of increasing attractant concentration. The K-S equations predict that bacteria will aggregate at the maxima of the attractant concentration, and this is not always observed: for rapidly varying concentration gradients, the peak in bacterial concentration is some distance away, lying on a ring. This is the "volcano effect". Starting from a simplified biochemical description of each bacterium and then extracting population level models, we show how to bridge these two regimes (K-S and volcanic). The results are verified against stochastic simulations of virtual bacteria. We also discuss applications to the more complex chemotactic process where the bacteria are themselves producing the chemoattractant.
Center for Computational Science, Stanley Thomas Hall 402, New Orleans, LA 70118 email@example.com