Modeling the Acid−Base Properties of Bacterial Surfaces:  A Combined Spectroscopic and Potentiometric Study of the Gram-Positive Bacterium Bacillus subtilis

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: tripple bond COOH, tripple bond NH+, and tripple bond 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 tripple bond NH+, tripple bond POH, and tripple bond COOH species were determined in the fit. A second approach is presented in which the ratio determined by XPS of the total concentrations of tripple bond NH+ to tripple bond PO- sites is relaxed. The total concentration of tripple bond PO- sites was determined in the fit, while the deprotonation constant for tripple bond 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.

Cell surface acid-base properties of the cyanobacterium Synechococcus : Influences of nitrogen source, growth phase and N:P ratios

“…Irrespective of the incubation time and the contents of the growth media, the FT-IR spectra collected for Synechococccus cells were relatively similar to each other and consistent with those obtained by other studies examining bacterial cells and proteins (after Zeroual et al, 1994;Kansiz et al, 1999;Benning et al, 2004;Jiang et al, 2004;Omoike and Chorover, 2004;Yee et al, 2004;Dittrich and Sibler, 2005;Kong and Yu, 2007;Leone et al, 2007;Meade et al, 2007;Movasaghi et al, 2008;Castro et al, 2010;Quilès et al, 2010;Alessi et al, 2014). This either means that there is a change in the type of phospholipids produced under these growth conditions, or the very sharp nature of this peak may indicate that the material may be more crystalline, and therefore, may be a relic of the sample preparation and relate to some residual media in the sample which crystallized upon drying.…”

“…The assignments of principal vibrational bands (compiled after Zeroual et al, 1994;Kansiz et al, 1999;Benning et al, 2004;Jiang et al, 2004;Omoike and Chorover, 2004;Yee et al, 2004;Dittrich and Sibler, 2005;Kong and Yu, 2007;Leone et al, 2007;Meade et al, 2007;Movasaghi et al, 2008;Castro et al, 2010;Quilès et al, 2010;Alessi et al, 2014 …”

Assignment of functional groups in Gram-positive bacteria

“…The reported spectral changes point to the deprotonation of the carboxyl group [6]. Similar correlations were observed by Ojeda in Aquabacteriumcommune and by Leonea in Bacillus subtilis [18,22]. Changes ascribed to symmetric (ν=1100 cm -1 ) and asymmetric (ν=1220 cm -1 ) stretching vibrations P=O (ν P=O ) of phosphate groups were also observed in the region of ν=1100-1220 cm -1 .…”

The product of microbial uranium reduction includes multiple species with U(IV)–phosphate coordination

“…3). Most likely this is not caused by changes of the amide bonds (in cell proteins) but is a consequence of deprotonation of the carboxyls and the overlap with the asymmetric carboxyl stretching vibration that typically occurs in the same frequency region (around 1550 cm À1 ) as amide II (Leone et al, 2007). The correlation between the observed spectral changes and the protonation/deprotonation of carboxylic groups is further corroborated by a principle component analysis (PCA) of the spectra in Fig.…”

“…Increasing pH results in the appearance of a new band at 1398 cm À1 and concomitant decrease of the signals from the protonated carboxyls. The new band originates from a symmetric stretching vibration of the deprotonated carboxylic group (Jiang et al, 2004;Leone et al, 2007). The increase in pH is also accompanied by a change in the relative intensities of the amide I and II bands (Fig.…”