Surface composition, surface properties, and adhesiveness of Azospirillum 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, poly saccharides, 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 degrees. 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.