Enthalpies and Entropies of Cd and Zn Adsorption onto Bacillus licheniformis and Enthalpies and Entropies of Zn Adsorption onto Bacillus subtilis from Isothermal Titration Calorimetry and Surface Complexation Modeling

Determining the thermodynamic driving force of metal-bacteria surface complexation is important for understanding why, from a thermodynamic perspective, these spontaneous reactions occur. We therefore determined the Gibbs energies, enthalpies, and entropies of Cd and Zn complexation onto Bacillus licheniformis and of Zn complexation onto Bacillus subtilis using surface complexation modeling and isothermal titration calorimetry. Our results indicated that Cd and Zn complexation onto Bacillus licheniformis is entropically driven at low pH and enthalpically driven at circumneutral pH. Zn complexation onto Bacillus subtilis is entropically driven, which suggests that Bacillus licheniformis has different donor ligands dominating reactivity around circumneutral pH.