The effect of culture condition and ionic strength on proton adsorption at the surface of the extreme thermophile Acidianus manzaensis

Some previously published studies have used surface complexation theory to model proton adsorption in mesophilic bacteria. However, few experiments, to date, have investigated the effects of cultivation conditions and ionic strength on proton interactions among extreme thermophile archaea. In this study, we characterize proton adsorption of the extreme thermophile Acidianus manzaensis by performing acid–base titrations and electrophoretic mobility measurements in NaNO3 solution (0.001–0.1 M), as well as Attenuated Total Reflection Fourier Transformed Infrared Spectroscopy (ATR-FTIR) with pH 2–10. Equilibrium thermodynamics (Donnan model) were applied to predict trends of ion adsorption at the archaea–water interface. We observed that the acidic properties of the A. manzaensis surface were significantly related to culture conditions and ionic strength. The buffering capacity of A. manzaensis cultivated with pyrite was much less than that of A. manzaensis cultured with sulfur. Furthermore, with increasing pH value, the buffering capacity increased and the surface charge became increasingly negative. To our knowledge, A. manzaensis has the highest buffering capacity of per unit wet biomass among all microbes studied. In conclusion, based on our model, the acid–base properties of the cell wall of A. manzaensis can be characterized by invoking three distinct types of cell wall functional groups: Carboxyl, phosphoryl, and amide groups, which were also verified by ATR-FTIR.