Numerical modeling of potential profiles in electrical double layer of Acidithiobacillus ferrooxidans cell surface

The surface charge density, space charge density, surface potential (φ₀) and Donnan potential (φ_Don) on the surface of Acidithiobacillus ferrooxidans cultivated with elemental sulfur (S-A.ferrooxidans) were calculated by numerical simulation using the ion-impenetrable and ion-penetrable models. Zeta potential measurement show that the isoelectric point (IEP) of S-A.ferrooxidans is higher than that of bacterium cultured with Fe²⁺. It is concluded from fitting data by ionizable surface group model that S-A.ferrooxidans surface probably consists of much proteins, the ionization of amino group of which causes higher IEP (> 2). The ion-penetrable model reveals that φ₀ and φ_Don decrease rapidly at pH < 5 but hardly change when pH is 6-7. The thickness of electrical double layer of S-A.ferrooxidans is estimated as 5 nm. The electrical double layer of bacterial cell surface may have significant implications for ions transfer and nutrient transport, but their interaction is unfavorable for bacterial aggration.