(394i) Population Dynamics of Chemotactic Bacteria in Response to Multiple Chemical Stimuli

Chemotactic bacteria sense and respond to temporal and spatial gradients of chemical cues in their surroundings. This phenomenon plays a critical role in many microbial processes such as groundwater bioremediation, microbially-enhanced oil recovery, nitrogen fixation in legumes, and pathogenesis of disease. Chemical heterogeneity in these natural systems may produce numerous competing signals from various directions. Predicting the migration behavior of bacterial populations under such conditions is necessary for designing effective treatment strategies.

In this study we observed the response of Escherichia coli to a mixture of chemoattractant (methylaspartate) and a chemorepellant (nickel ion) in various spatial configurations. The goal was to predict the overall response based on transport parameters that quantified the chemotactic response to individual chemicals. We used a combination of experimental assays and mathematical modeling. A microfluidic device designed to generate steady, linear concentration profiles was used to evaluate the chemotaxis transport properties for each chemoeffector separately. Then bacterial concentration profiles for various mixture configurations were compared to model predictions. We initially considered a modeling approach using an additive response in which the macroscopic expressions for the chemotactic velocities were simply added together assuming a negative velocity for the chemorepellant. Because the chemosensory mechanism is well-documented for E. coli, we also considered a molecular-level modeling approach that incorporated several key steps in the pathway in order to deduce the mechanism by which bacteria process multiple signal inputs to generate an integrated response. Finally, we explored the separation of a mixed microbial culture based on the differential response to a single chemoeffector.