Metal adsorption onto bacterial surfaces, bacterial adsorption onto mineral surfaces, and bacterially mediated mineral dissolution can control mass transport in bacteria-bearing geologic systems. The research in this dissertation provides a mechanistic understanding of some of these important biogeochemical processes.
In Chapter 2, the adsorption of the gram-positive bacterium Bacillus subtilis was compared with adsorption of the gram-negative bacterium Pseudomonas mendocina onto Fe-oxyhydroxide-coated and uncoated quartz grains as a function of pH and bacteria : mineral mass ratio. The data show that the presence of Fe-oxyhydroxide-coatings on quartz surfaces significantly enhances the adsorption of bacteria and that in general the extent of adsorption decreases with increasing pH and with decreasing bacteria : mineral mass ratio. B. subtilis adsorbs to a greater extent than does P. mendocina onto the surface of the Fe-coated quartz. The adsorption data was modeled using a semi-empirical chemical equilibrium model.
Chapter 3 describes a study of the effect of metabolism on Cd adsorption onto Gram-positive and Gram-negative bacterial cells. Metabolizing Gram-positive cells adsorbed significantly less Cd than non-metabolizing cells. Gram-negative cells showed little difference in Cd adsorption onto metabolizing and non-metabolizing cells.
In Chapter 4, pH dependent measurements of Cd2+ and H2AsO4- adsorption onto Shewanella oneidensis were used as an indirect probe of the bacterial surface charge. Cd2+ exhibits typical cation adsorption behavior. H2AsO4- adsorption is negligible over the entire pH range studied. These observed adsorption behaviors are most consistent with the presence of negative charge on the bacterial surface. Based on this conclusion,
titration and Cd adsorption data for S. oneidensis were modeled using only acidic functional group sites.
In Chapter 5, the production of siderophores by Pseudomonas mendocina under Fe-limited conditions is described as a function of Fe source: supplied in dissolved form, as Fe-containing kaolinite, and a no-Fe-added control. Production of siderophore on a per-cell basis decreased in the order: no-Fe-added control>kaolinite>FeEDTA. Although more siderophore per cell was produced in the most stressed system, more total siderophore was produced in the least stressed system. This is due to the presence of a larger total population size in the least stressed system.