Surface of Lactic Acid Bacteria: Relationships between Chemical Composition and Physicochemical Properties

The surface chemical composition and physicochemical properties (hydrophobicity and zeta potential) of two lactic acid bacteria, Lactococcus lactis subsp. lactis bv. diacetilactis and Lactobacillus helveticus, have been investigated using cells harvested in exponential or stationary growth phase. The surface composition determined by X-ray photoelectron spectroscopy (XPS) was converted into a molecular composition in terms of proteins, polysaccharides, and hydrocarbonlike compounds. The concentration of the last was always below 15% (wt/wt), which is related to the hydrophilic character revealed by water contact angles of less than 30°. The surfaces of L. lactis cells had a polysaccharide concentration about twice that of proteins. The S-layer of L. helveticus was either interrupted or crossed by polysaccharide-rich compounds; the concentration of the latter was higher in the stationary growth phase than in the exponential growth phase. Further progress was made in the interpretation of XPS data in terms of chemical functions by showing that the oxygen component at 531.2 eV contains a contribution of phosphate in addition to the main contribution of the peptide link. The isoelectric points were around 2 and 3, and the electrophoretic mobilities above pH 5 (ionic strength, 1 mM) were about −3.0 × 10(−8) and −0.6 × 10(−8) m(2) s(−1) V(−1) for L. lactis and L. helveticus, respectively. The electrokinetic properties of the latter reveal the influence of carboxyl groups, while the difference between the two strains is related to a difference between N/P surface concentration ratios, reflecting the relative exposure of proteins and phosphate groups at the surface

Oxidation of proteins adsorbed on hemodialysis membranes and model materials.

The cleaning of cellulosic hemodialysis membrane Cuprophan and model materials (glass; polystyrene and polypropylene, as such and surface-oxidized), conditioned by adsorption of blood plasma proteins (HSA, fibrinogen, IgG) was investigated in vitro. Sodium hypochlorite (NaClO) and Renalin, a product containing hydrogen peroxide and peroxyacetic acid, were used as cleaning reagents. X-ray photoelectron spectroscopy and the use of radiolabeled fibrinogen demonstrated the presence of varying amounts of a polypeptidic residue, with sulfur brought to a high oxidation stage (sulfonate-like). The trends were the same for the three proteins regarding the effectiveness of the oxidizer and the influence of the surface properties. NaClO was much more effective than Renalin to remove the adsorbed proteins. The proteins adsorbed on Cuprophan were more sensitive to the oxidizers, when compared with proteins adsorbed on other materials. This may be due to both the lower protein-surface affinity, as indicated by radiochemical measurements, and the sensitivity of the material itself to the oxidizer, as revealed by weight loss measurements. These results support the attribution of hemocompatibility improvement after regeneration of Cuprophan with Renalin to the masking of the activating surface by a residue from previously adsorbed proteins

Direct Probing of the Surface Ultrastructure and Molecular Interactions of Dormant and Germinating Spores of Phanerochaete chrysosporium

Atomic force microscopy (AFM) has been used to probe, under physiological conditions, the surface ultrastructure and molecular interactions of spores of the filamentous fungus Phanerochaete chrysosporium. High-resolution images revealed that the surface of dormant spores was uniformly covered with rodlets having a periodicity of 10 ± 1 nm, which is in agreement with earlier freeze-etching measurements. In contrast, germinating spores had a very smooth surface partially covered with rough granular structures. Force-distance curve measurements demonstrated that the changes in spore surface ultrastructure during germination are correlated with profound modifications of molecular interactions: while dormant spores showed no adhesion with the AFM probe, germinating spores exhibited strong adhesion forces, of 9 ± 2 nN magnitude. These forces are attributed to polysaccharide binding and suggested to be responsible for spore aggregation. This study represents the first direct characterization of the surface ultrastructure and molecular interactions of living fungal spores at the nanometer scale and offers new prospects for mapping microbial cell surface properties under native conditions