Quantifying bacteria-contaminant interactions (Bacillus subtilis).

Experiments were conducted to probe for the existence of positive sites on the cell wall of the Gram-positive bacterium Bacillus subtilis through a combination of electrophoretic mobility measurements and anion adsorption experiments with iodide. Iodide adsorption onto Bacillus subtilis was measured as a function of pH, ionic strength, solid:solute ratio, and time. The experimental data were interpreted using a surface complexation approach. The I- adsorption data were best fit with a single surface site reaction, with the iodide ion forming a surface complex with the positively-charged amino functional group located on the bacterial cell wall: R-NH3+ + I- ↔ R-NH3-I- (log K = 8.9 +/- 0.2). Electrophoretic mobility measurements, conducted as a function of pH and electrolyte ionic strength, support the presence of positively-charged surface functionalities at low pH under experimental conditions. Amino-anion stability constants may be incorporated into surface complexation models in order to accurately predict the bioavailability and exposure risk of radioiodine in the environment. Additional anion adsorption experiments in metal-anion-bacteria ternary systems were conducted to determine the effect of multi-valent cations on the electrokinetic properties of the cell wall and its ability to adsorb anions. Adsorption results demonstrated that both anions and (oxy)anions have a pH-dependent affinity for the cell wall of B. subtilis below pH 5. Increased adsorption of anions at higher pH values (\u3epH 4) was observed in the presence of 1 mM Ca. In contrast, no significant little adsorption was observed at similar pH values in the presence of both 0.1 mM and 1 mM La. The presence of positively-charged ions at the bacteria-solute interface can influence the mobility of anionic contaminants and further refines the surface complex approach. Source: Masters Abstracts International, Volume: 42-03, page: 0895. Adviser: David Fowle. Thesis (M.Sc.)--University of Windsor (Canada), 2003