Kinetics of bacterial potentiometric titrations: The effect of equilibration time on buffering capacity of Pantoea agglomerans suspensions

Several recent studies have made use of continuous acid–base titration data to describe the surface chemistry of bacterial cells as a basis for accurately modelling metal adsorption to bacteria and other biomaterials of potential industrial importance. These studies do not share a common protocol; rather they titrate in different pH ranges and they use different stability criteria to define equilibration time during titration. In the present study we investigate the kinetics of bacterial titrations and test the effect they have on the derivation of functional group concentrations and acidity constants. We titrated suspensions of Pantoea agglomerans by varying the equilibration time between successive titrant additions until stability of 0.1 or 0.001 mV s−1 was attained. We show that under longer equilibration times, titration results are less reproducible and suspensions exhibit marginally higher buffering. Fluorescence images suggest that cell lysis is not responsible for these effects. Rather, high DOC values and titration reversibility hysterisis after long equilibration times suggest that variability in buffering is due to the presence of bacterial exudates, as demonstrated by titrating supernatants separated from suspensions of different equilibration times. It is recommended that an optimal equilibration time is always determined with variable stability control and preliminary reversibility titration experiments.

Graph demonstrates poor reproducibility of bacterial titration results under slow equilibration of suspension (0.001 pH min−1 stability criteria).Figure optionsDownload high-quality image (53 K)Download as PowerPoint slideHighlights
► Stability criteria can influence titration results of bacterial surfaces.
► Longer equilibration times result in additional proton buffering.
► Additional buffering is associated with the production of exudates.
► Fast equilibration is recommended.