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  • 1.
    Leone, Laura
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Ferri, Diego
    Umeå University, Faculty of Science and Technology, Chemistry.
    Manfredri, Carla
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Chemistry.
    Modeling the Acid-Base Properties of Bacterial Surfaces: A Combined Spectroscopic and Potentiometric Study of the Gram-Positive Bacterium Bacillus subtilis2007In: Environmental Science & Technology, Vol. 41, no 18, p. 6465-71Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Leone, Laura
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Surface characterization of the Gram-positive bacteria Bacillus subtilis-an XPS study2006In: Surface and Interface Analytsis, Vol. 38, p. 202-5Article in journal (Refereed)
    Abstract [en]

    Interactions at the bacteria-solid interface in aquatic environments are of crucial importance in biofilm formation processes. The characterization of microbial surfaces properties is therefore a very important step for the understanding of these interactions. In this study, XPS spectra of Bacillus subtilis wet pastes centrifuged from suspensions over a span of pH values were recorded using a fast-freezing procedure. The chemical composition of the bacterial surface was elucidated and the presence of surface sites containing carboxylate, phosphate and amine functional groups was established. It was possible to distinguish between charged and uncharged amine sites on the surface and follow their deprotonation reactions as a function of pH. It is suggested that increased metabolic activity around the physiological pH results in the excretion of proteins and/or peptides which are possibly related to the production of extracellular polymeric substances (EPS). Copyright © 2006 John Wiley & Sons, Ltd.

  • 3.
    Ramstedt, Madeleine
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Leone, Laura
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bacterial surfaces in geochemistry: how can x-ray photoelectron spectroscopy help?2019In: Analytical geomicrobiology: a handbook of instrumental techniques / [ed] Janice P. L. Kenney, Harish Veeramani, Daniel S. Alessi, Cambridge: Cambridge University Press , 2019, p. 262-287Chapter in book (Other academic)
    Abstract [en]

    Processes occurring at surfaces and interfaces are very important in environmental systems, necessitating surface-specific characterization tools that can help us understand processes at and specific properties of surfaces and interfaces, and their role in biogeochemical systems. This chapter describes the use and application of X-ray photoelectron spectroscopy (XPS) to study interfacial processes of relevance for geomicrobiology. Examples are given from studies determining cell wall composition, acid–base properties, cell surface charge, metal adsorption onto bacterial cells, and bacterial surface–induced precipitation of secondary minerals. As XPS is an ultrahigh-vacuum technique, several sample preparation methods have been applied to enable analysis of bacterial samples, including analysis of freeze-dried samples as well as frozen bacterial suspensions. These are described and discussed alongside advantages and disadvantages of different approaches, with a special focus on fast-freezing and the cryogenic technique.

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