Experimental Studies of Bacterial Sorption: The Role of Extracellular Polymeric Substances (EPS), Sorption of Per- and Polyfluoroalkyl Substances (PFAS), and Controls on Sulfhydryl Site Concentrations

Bacteria are present in virtually all environments on Earth where liquid water exists, and where they are capable of affecting the transport of a wide range of contaminants from heavy metals to complex organic compounds. In chapter 2, I describe a study of the effects of extracellular polymeric substances (EPS) on bacterial adsorption, and the importance of sulfhydryl binding sites on the EPS molecules. We observed that removal of EPS material from bacterial cells, via cation exchange resin, does not significantly change the mass-normalized extent of Cd adsorption onto the biomass. Our results suggest that the concentration of binding sites on the EPS, and the affinity of these sites to bind Cd, are similar to those on the cell surface for the three bacterial species studied, but that the chemical identity of these sites varies between the cell surface and the EPS molecules. Chapter 3 reports the results of a study of the capability of bacteria to sorb per- and polyfluoroalkyl substances (PFAS). We used a novel analytical technique involving particle induced gamma-ray emission (PIGE) spectroscopy to quantify PFAS concentrations in solution using total fluorine measurements. Our results indicate that Gram-positive and Gram-negative bacterial cells are capable of removing PFOA and PFOS from solution, and that PFAS sorption onto bacteria is likely a surface process involving both electrostatic and hydrophobic binding mechanisms. In chapter 4. I describe the results of a study of the effects of varying the concentration and identity of electron donors on bacterial surface and EPS sulfhydryl site concentrations. Our results suggest that total energy availability represents a strong control on the ability of bacterial cells to produce sulfhydryl binding sites and that there are factors other than electron donor concentration that also influence sulfhydryl site production by bacteria.