- 2:10 PM

Stochastic Modeling of Bacterial Migration in Porous Media

Tran D. Trinh, Whitney L. Hovan, and Christian M. Lastoskie. University of Michigan, 1351 Beal Avenue, Ann Arbor, MI 48109-2125

The mechanisms of microbial transport and biofilm formation on surfaces are of interest to chemical and environmental engineers. For some processes, e.g. wastewater treatment or in situ groundwater remediation, biofilm development is actively sought, whereas in other applications, e.g. potable water distribution or medical device implantation, it is desirable to prevent biofilm growth. Given that biofilm formation on a surface is preceded by microbial transport and adhesion to the surface, predictive models are of value that describe the movement of motile cell populations in complex heterogeneous porous environments.

Chemotactic motile bacteria have the ability to redirect their migration in response to concentration gradients of nutrients, electron acceptors, toxins or other relevant chemical stimuli. Microbial species that can exploit chemotaxis possess a competitive ecological advantage over nonchemotactic organisms and can more readily migrate to and establish biofilms in nutrient-rich domains.

For chemoattractants that are consumed or cometabolized by bacteria, the migration of the planktonic cell population is governed by a reaction-diffusion equation in which chemoattractant gradients are formed at the microscopic scale. A stochastic cellular dynamics simulation algorithms has been developed to model microbial chemotaxis in response to the consumption of metabolizable chemoattractants in heterogeneous porous media. In the cellular dynamics simulation method, the trajectories of a population of motile cells are obtained from the individual motion parameters characteristic of the cellular species (e.g. the swimming speed, basal turning probability and turn-angle correlation function), and from the biased random-walk motion that results from attenuation of cell migration to the evolving chemoattractant concentration field that is detected by the cohort of cells.

In this paper, cellular dynamics simulations of Eschereschia coli and Pseudomonas stutzeri chemotaxis are reported in bulk solution and in porous media. It is noted that for consumable chemoattractants, an enhanced chemotactic motility can be observed for migration through porous media relative to chemotaxis in bulk solution. Simulation results are reported for cell migration through various pore geometries and cell deposition rates on surfaces are predicted for varying concentration gradients of selected E. coli chemoattractants and chemorepellents. The application of the cellular dynamics simulation methodology to the modeling of quorum sensing is discussed.