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Modeling the acid-base properties of bacterial surfaces: A combined spectroscopic and potentiometric study of the gram-positive bacterium Bacillus subtilis

Leone, Laura; Ferri, Diego; Manfredi, Carla; Persson, Per LU ; Shchukarev, Andrei; Sjoberg, Staffan and Loring, John (2007) In Environmental Science & Technology 41. p.6465-6471
Abstract
In this study, macroscopic and spectroscopic data were combined to develop a surface complexation model that describes the acid-base properties of Bacillus subtilis. The bacteria were freeze-dried and then resuspended in 0.1 M NaCl ionic medium. Macroscopic measurements included potentiometric acid-base titrations and electrophoretic mobility measurements. In addition, ATR-FTIR spectra of wet pastes from suspensions of Bacillus subtilis at different pH values were collected. The least-squares program MAGPIE was used to generate a surface complexation model that takes into account the presence of three acid-base sites on the surface: COOH, NH+, and PO-, which were identified previously by XPS measurements. Both potentiometric titration data... (More)
In this study, macroscopic and spectroscopic data were combined to develop a surface complexation model that describes the acid-base properties of Bacillus subtilis. The bacteria were freeze-dried and then resuspended in 0.1 M NaCl ionic medium. Macroscopic measurements included potentiometric acid-base titrations and electrophoretic mobility measurements. In addition, ATR-FTIR spectra of wet pastes from suspensions of Bacillus subtilis at different pH values were collected. The least-squares program MAGPIE was used to generate a surface complexation model that takes into account the presence of three acid-base sites on the surface: COOH, NH+, and PO-, which were identified previously by XPS measurements. Both potentiometric titration data and ATR-FTIR spectra were used quantitatively, and electrostatic effects at the charged bacterial surface were accounted for using the constant capacitance model. The model was calculated using two different approaches: in the first one XPS data were used to constrain the ratio of the total concentrations of all three surface sites. The capacitance of the double layer, the total buffer capacity, and the deprotonation constants of the NH+, POH, and COOH species were determined in the fit. A second approach is presented in which the ratio determined by XPS of the total concentrations of NH+ to PO- sites is relaxed. The total concentration of PO- sites was determined in the fit, while the deprotonation constant for POH was manually varied until the minimization led to a model which predicted an isoelectric point that resulted in consistency with electrophoretic mobility data. The model explains well the buffering capacity of Bacillus subtilis suspensions in a wide pH range (between pH = 3 and pH = 9) which is of considerable environmental interest. In particular, a similar quantitative use of the IR data opens up possibilities to model other bacterial surfaces at the laboratory scale and help estimate the buffering capacity of carboxylate containing compounds in natural samples. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Environmental Science & Technology
volume
41
pages
6465 - 6471
publisher
The American Chemical Society
external identifiers
  • scopus:34548806948
ISSN
1520-5851
DOI
10.1021/es070996e
language
English
LU publication?
no
id
d2e3bde5-1cc4-4b50-9bda-52d6a06e1a4c (old id 4332454)
date added to LUP
2014-03-04 09:39:09
date last changed
2017-05-21 04:15:04
@article{d2e3bde5-1cc4-4b50-9bda-52d6a06e1a4c,
  abstract     = {In this study, macroscopic and spectroscopic data were combined to develop a surface complexation model that describes the acid-base properties of Bacillus subtilis. The bacteria were freeze-dried and then resuspended in 0.1 M NaCl ionic medium. Macroscopic measurements included potentiometric acid-base titrations and electrophoretic mobility measurements. In addition, ATR-FTIR spectra of wet pastes from suspensions of Bacillus subtilis at different pH values were collected. The least-squares program MAGPIE was used to generate a surface complexation model that takes into account the presence of three acid-base sites on the surface: COOH, NH+, and PO-, which were identified previously by XPS measurements. Both potentiometric titration data and ATR-FTIR spectra were used quantitatively, and electrostatic effects at the charged bacterial surface were accounted for using the constant capacitance model. The model was calculated using two different approaches: in the first one XPS data were used to constrain the ratio of the total concentrations of all three surface sites. The capacitance of the double layer, the total buffer capacity, and the deprotonation constants of the NH+, POH, and COOH species were determined in the fit. A second approach is presented in which the ratio determined by XPS of the total concentrations of NH+ to PO- sites is relaxed. The total concentration of PO- sites was determined in the fit, while the deprotonation constant for POH was manually varied until the minimization led to a model which predicted an isoelectric point that resulted in consistency with electrophoretic mobility data. The model explains well the buffering capacity of Bacillus subtilis suspensions in a wide pH range (between pH = 3 and pH = 9) which is of considerable environmental interest. In particular, a similar quantitative use of the IR data opens up possibilities to model other bacterial surfaces at the laboratory scale and help estimate the buffering capacity of carboxylate containing compounds in natural samples.},
  author       = {Leone, Laura and Ferri, Diego and Manfredi, Carla and Persson, Per and Shchukarev, Andrei and Sjoberg, Staffan and Loring, John},
  issn         = {1520-5851},
  language     = {eng},
  pages        = {6465--6471},
  publisher    = {The American Chemical Society},
  series       = {Environmental Science & Technology},
  title        = {Modeling the acid-base properties of bacterial surfaces: A combined spectroscopic and potentiometric study of the gram-positive bacterium Bacillus subtilis},
  url          = {http://dx.doi.org/10.1021/es070996e},
  volume       = {41},
  year         = {2007},
}