Predictive Modeling of Metal Adsorption Onto Bacterial Surfaces in Geologic Settings

Bacterial surfaces are capable of adsorbing large quantities of metals, and are thought to partly control the distribution, fate, and bioavialability of metals in near-surface geologic systems. Geochemical models have been employed that are capable of predicting the extents of metal adsorption onto specific bacterial species under laboratory conditions. However, our ability to extrapolate these models to predict the distribution and fate of metals in realistic geologic systems is limited. This dissertation presents the work of a number of closely linked, but individual studies that attempt to quantitatively describe the adsorption reactions on bacterial surfaces so that we can predict the extent and importance of these reactions in geologic systems. This dissertation is the synthesis of more than 300 individual experiments (batch adsorption experiments, potentiometric titrations, chemotaxis experiments, etc.) and corresponding surface complexation models and modeling parameters that test the following questions: (Ch. 2) Are modeling parameters developed from laboratory experiments conducted using bacteria treated with acid similar to those for bacteria in natural (non-acid treated) systems? (Ch. 3 & 4) Do consortia of bacteria from natural and contaminated systems exhibit universal adsorption behavior? (Ch. 5) How will salt concentration affect the adsorption behavior of bacteria over the ionic strength ranges found in natural systems? (Ch. 6) Can adsorption models be used to predict bacterial chemotaxis in complex multicomponent systems?

The results from these studies demonstrate that (Ch. 2) acidic solutions can damage the bacterial surface by displacing structurally bound Mg and Ca, (Ch. 3 & 4) consortia of bacteria from uncontaminated environments exhibit similar extents of Cd adsorption, while consortia of bacteria from contaminated environments adsorb Cd to much greater extents, (Ch. 5) ionic strength has a negligible impact on the adsorption of protons, Cd, and Pb onto bacterial surfaces, and (Ch. 6) adsorption reactions can control bacterial chemotactic responses and chemical equilibrium models can be used to predict these responses in multicomponent systems. These studies are successful in bringing us closer than ever before to predicting the true extent of bacterial surface adsorption reactions in real systems.