An experimental and computational study of the role of cytochrome 2 in the adhesion of Acidithiobacillus ferrooxidans to pyrite in fresh and saline water

The use of Acidithiobacillus ferrooxidans is emerging as an alternative to enhance the performance of leaching and flotation in copper mining. This bacterium adheres to minerals like pyrite, oxidizing it, which facilitates its dissolution in leaching and depression in flotation. Acidithiobacillus ferrooxidans interacts with pyrite through Cytochrome 2, a membrane protein that induces oxidation. In this work we performed an experimental and computational study of the role of Cytochrome 2 in the adhesion of Acidithiobacillus ferrooxidans to pyrite in fresh and saline water, using a numerical model based on the Poisson-Boltzmann equation and the Lennard-Jones potential that has atomic resolution. Our results indicate that the electrostatic interaction between pyrite and Cytochrome 2 dictates the pH dependence of the adhesion of Acidithiobacillus ferrooxidans as a whole. Also, we found that at low salinity the electrostatic interaction is dominated by the total charge of both the protein and the pyrite surface, however, the shielding effect at higher salt concentrations makes local interactions more relevant, which modifies the pH at which adhesion peaks. This work serves as motivation to rationally tune conditions to optimize the leaching and flotation processes through biological reagents.