Surface properties of microbial cells and their role in adhesion and flocculation

Heterogeneity of Surfaces of Subgingival Bacteria as Detected by Zeta Potential Measurements

Porphyromonasgingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans (A.a.) are Gram-negative bacteria which are implicated in various forms of periodontal disease. The Gram-positive Peptostreptococcus micros may also play an important role. For investigation of the possible adhesion and colonization mechanisms of these organisms, the charge properties of the outermost layers of bacterial cell surfaces were studied through the measurement of zeta potentials at various pH values. Eleven fresh clinical isolates, representing the four species, and one laboratory strain, P. gingivalis W83, were examined. Eleven of the 12 strains displayed heterogeneity with respect to pH-dependent zeta potentials. Within single cultures of each of these strains, two distinct populations of cells were found, one which was more negatively charged than the other. For the Gram-negative strains, the more negatively charged subpopulation was in the majority, while the P. micros strains appeared to be composed mainly of a less-negatively-charged subpopulation. Vesicles prepared from two strains displayed the same pH dependence and heterogeneity of zeta potentials as the parent cells. An A.a. strain which was passaged several times in fluid medium had lost its fimbriae and became homogeneous with respect to charge.

XPS analysis of chemical functions at the surface of Bacillus subtilis

The surface chemical composition of nine strains of Bacillus subtilis was determined by X-ray photoelectron spectroscopy. Regressions between elemental concentrations and concentrations associated with different components of C1s, N1s, and O1s peaks provided a more precise validation of the procedure used for peak decomposition and allowed the assignment of the peak components to be completed or strengthened. The component of the O1s peak appearing around 531.2 eV was shown to contain a contribution of oxygen from phosphate groups (PO, PO-), the other contribution being due to oxygen involved in amide functions. The surface negative charge may be fully attributed to phosphate groups, despite the observation of two types of zeta potential vs pH curves. The strains exhibiting a sharp variation of the zeta potential (range of -35 to -55 mV) between pH 2 and 4.7 were characterized by a high phosphate surface concentration and by an excess (about 25%) of phosphate with respect to the sum of potassium, an exchangeable cation, and protonated nitrogen, attributed to protein or to alanine involved in teichoic acids.

Effects of glucose and mannose on the flocculation behavior of Saccharomyces cerevisiae at different life stages

The temporal flocculation behavior of Saccharomyces cerevisiae at different life stages is investigated using glucose and mannose as the different carbon sources, and the temporal variations of cell size, zeta potential and stability ratio of cell suspension are measured. It is found that the largest cell size and the lowest stability ratio of cell suspension occurred at the middle period of the exponential growth phase independent of carbon sources. The colloidal aspect was analyzed by using the DLVO theory, and indicated that the gravitational force plays a major role in determining the flocculation behavior of yeast cells.

The ζ-potential of the endogenous particles of a wine of Champagne in relation to the foaming behaviour

It was shown that the endogenous particles of the champagnes influence the lifetime, and not the maximum expansion of their evanescent foam (Food Hydrocolloids (1999) 12, 217-226). Actually, champagnes are electrolytic solutions with pH 3 and ionic strength equal to 0.02 mol/l in which bentonites, diatomites, and yeast cells are the more numerous colloids and particles present. In this context, we have investigated the electrophoretic properties of these particles to determine whether they can electrostatically interact with the foam bubbles. Results are that in model alcoholic solutions of proteins at same pH and ionic strength as the champagne, the zeta-potential was not vanishing whereas it dropped down to zero in wines. The zeta-potential of the particles does not vanish either when they are suspended in nanofiltered wines on molecular weight cut-off membrane (porosity=200-300 Da) or when the wines are basified upon addition of sodium hydroxide. This particular behaviour was tentatively assigned to the adsorption of some endogenous organic cationic ions on the particle surfaces, which screened out their electrostatic charge. The possible candidates are discussed.

Surface composition, surface properties, and adhesiveness ofAzospirillum brasilense—variation during growth

The surface chemical composition, the physicochemical properties, and the adhesiveness of Azospirillum brasilense have been investigated during growth in Luria–Bertani* rich medium. The surface elemental composition obtained by X-ray photoelectron spectroscopy was converted into a molecular composition in terms of model constituents: proteins, polysaccharides, and hydrocarbon-like compounds. The protein content increased during growth, from 30 (exponential phase cells) to 50% (stationary phase cells), concomitantly with a decrease in the polysaccharide content, from 60 to 35%. These modifications were related to a change in cell surface hydrophobicity, i.e., to an increase of the water contact angle from 20 to 60°. No difference of electrophoretic mobility was detected between cells harvested in the exponential phase and cells harvested in the stationary phase. The increase of both cell surface protein concentration and cell surface hydrophobicity during growth was correlated with an increase of cell adhesiveness to model supports. This points to the involvement of cell surface proteins and cell surface hydrophobicity in the adhesion process.Key words: Azospirillum brasilense, surface composition, hydrophobicity, adhesiveness, X-ray photoelectron spectroscopy.

Influence of relA locus on electrophoretic mobility of a stringent/relaxed Escherichia coli K 12 strain pair

Stringent (relA+) and relaxed (rel A-) controlled Escherichia coli cells differ in their regulation of many biochemical pathways such as phospholipid and lipopolysaccharide metabolism (LPS) after amino acid limitation. Because such differences could result in various cell envelopes, cells of stringent controlled E. coli strain CP78 (relA+) and relaxed controlled E. coli strain CP79 (relA) were studied regarding their electrophoretic mobility. The graphs of the mobility distributions of both strains were different: cells of strain CP79 caused secondary peaks in addition to the main peaks whereas the mobility distributions of cells of strain CP78 showed only one maximum. In the pH range from 6.0 to 8.0 the location of the main peaks of cells of strain CP79 were changed to less negative values after induction of relaxed response. In contrast to this the stringent response in strain CP78 caused no change of the mobility distributions.