Physico-chemical surface properties of rhizobacteria and their adhesion to rice roots

Contribution of the comonomers to the bulk and surface properties of methacrylate copolymers

Relationships between formulation, bulk properties, and surface properties are investigated on series of copolymers prepared with hydroxyethylmethacrylate (HEMA), methylmethacrylate (MMA), and ethylmethacrylate (EMA) monomers, and on the homopolymers PMMA and PHEMA. The bulk water content, swelling ratio, and static (sessile drop and captive bubble) and dynamic (Wilhelmy plate technique) contact angles and the electrokinetic potential (streaming potential) are measured. The bulk water content and swelling ratio of HEMA copolymers are proportional to the amount of HEMA and are linearly correlated to the contact angle hysteresis. Periodic instabilities in the wetting cycles, similar to Haines jumps, are observed with HEMA copolymers and support a bidirectional relaxation of the hydrophilic groups respectively towards external water and capillary water. The origin of the electrokinetic potential of these nonionizable polymers is attributed to specific adsorption of [Formula: see text] ions. Its dependence on surface hydrophobicity and statistical length of the side-chains is interpreted in terms of the properties of water molecules near the interface.

Influence of phosphate on bacterial adhesion onto iron oxyhydroxide in drinking water

The transport and storage of drinking water in water distribution systems can modify its initial composition and properties. The accumulation of bacteria on corroded pipes is prejudicial and may lower the microbiological quality of the water. Previous results have shown that when pipes are highly corroded, the addition of phosphate, used as an anticorrosion treatment, decreases the bacterial concentration in the water. We studied the possibility of using phosphate to reverse the surface charge of iron oxyhydroxide (FeOOH) to limit bacterial adhesion. Iron oxyhydroxide (IOH) particles and Escherichia coli SH 702 were used as models of corrosion products and bacterial contamination, respectively. Electrophoresis was used to characterize the initial surface charges of both types of particles and the modifications that occurred after the addition of phosphate anions. Flow cytometry and adhesion assays were used to build adsorption isotherms of bacteria on IOH versus (phosphated-) IOH. X-ray photoelectron spectroscopy permitted to determine the chemical composition of the E. coli envelope and to discuss on functional groups responsible for bacterial surface properties. In the present conditions, adding phosphate to water allowed a decrease of 75% of the bacteria adhering to IOH.

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.