RANDOM-WALK CALCULATIONS FOR BACTERIAL MIGRATION IN POROUS-MEDIA

Bacterial migration is important in understanding many practical probl ems ranging from disease pathogenesis to the bioremediation of hazardo us waste in the environment. Our laboratory has been successful in qua ntifying bacterial migration in fluid media through experiment and the use of population balance equations and cellular level simulations th at incorporate parameters based on a fundamental description of the mi croscopic motion of bacteria. The present work is part of an effort to extend these results to bacterial migration in porous media. Random w alk algorithms have been used successfully to date in nonbiological co ntexts to obtain the diffusion coefficient for disordered continuum pr oblems. This approach has been used here to describe bacterial motilit y. We have generated model porous media using molecular dynamics simul ations applied to a fluid with equal sized spheres. The porosity is va ried by allowing different degrees of sphere overlap. A random walk al gorithm is applied to simulate bacterial migration, and the Einstein r elation is used to calculate the effective bacterial diffusion coeffic ient. The tortuosity as a function of particle size is calculated and compared with available experimental results of migration of Pseudomon as putida in sand columns. Tortuosity increases with decreasing obstac le diameter, which is in agreement with the experimental results.