IMPLICATIONS OF GENOME-BASED MICROBIOLOGICAL UNDERSTANDING FOR URANIUM FATE AND TRANSPORT

Microbially-mediated reductive immobilization of uranium and other redox-sensitive contaminants in the natural environment comprises a complex set of coupled microbial, geochemical, and hydrologic processes. We aim to significantly improve the predictive capabilities of numerical models by integrating advanced genome-based models of microbial processes (in silico models) with state-of-the-art reactive transport simulators. Genome-level understanding of microbial metabolism and other processes has recently grown in dramatic fashion, and several attributes of key microorganisms have direct relevance to uranium fate and transport (including bioremediation). We have coupled a genome-scale model of Geobacter metabolism to a field-scale uranium transport model at the Rifle, Colorado bioremediation research site. In support of this effort, we are also performing pore-scale simulations of microbial iron reduction (with comparisons to micromodel laboratory experiments) to test hypotheses regarding model scale effects. Our model includes the effects of local depletion of solid-phase iron oxides, effects of incomplete mixing and diffusion-limited transport of aqueous electron donor, development of biofilm structures, and partitioning of microorganisms between attached and planktonic states. Because the environment experienced by a microbial cell is micron-scale, and predictions of uranium transport are many orders of magnitude larger in scale, such understanding is needed to fully integrate genome-based models of microbial activity with predictive field-scale simulators.