Involvement of the Lipopolysaccharides of Azospirilla in the Interaction with Wheat Seedling Roots

The present study was undertaken to comparatively investigate the attachment capacities of Azospirillum brasilenseSp245 and its lipopolysaccharide-defective Omegon-Km mutants KM018 and KM252, as well as their activities with respect to the alteration of the morphology of wheat seedling root hairs. The adsorption dynamics of the parent Sp245 and mutant KM252 strains of azospirilla on the seedling roots of the soft spring wheat cv. Saratovskaya 29 were similar; however, the attachment capacity of the mutant KM252 was lower than that of the parent strain throughout the incubation period (15 min to 48 h). The mutation led to a considerable decrease in the hydrophobicity of the Azospirillumcell surface. The lipopolysaccharides extracted from the outer membrane of A. brasilenseSp245 and mutant cells with hot phenol and purified by chromatographic methods were found to induce the deformation of the wheat seedling root hairs, the lipopolysaccharide of the parent strain being the most active in this respect. The role of the carbohydrate moiety of lipopolysaccharides in the interaction of Azospirillumcells with plants is discussed.     

The effect of cooling rate, freeze-drying suspending fluid and culture age on the preservation of Campylobacter pylori

The effects of freezing rate, suspending fluid and age of culture on the ability of four strains of Campylobacter pylori to survive and recover from freeze-drying were examined. Freeze-drying by standard procedures generally resulted in an overall loss in viability of between 3 and 7 log units. The exact cause of poor recovery by C. pylori was not established but strain differences were detected, with NCTC 11637 (type strain) surviving better than NCTC 11638 and NCTC 11639. Recovery of the poorest growing strain (NE 26695) was notably more erratic. The largest loss in viability occurred at the primary drying stage. Losses resulting from freezing and secondary drying were less marked and the rate of freezing had only a marginal effect on recovery. Nineteen different freeze-drying suspending fluids were investigated. Overall the best recovery results were obtained with 5% inositol-broth (or horse serum) plus 25% glucose, at pH 7.0, in which loss of viability was typically about 4 log units. Other factors, such as age of culture and number of viable bacteria in the before-dry suspension, did not have a significant effect on survival. We conclude from these results that C. pylori can survive freeze-drying, albeit in small numbers, but the degree of recovery is apparently largely strain dependent.     

Self-assembly and secondary structure of beta-casein

The secondary structure alterations during isothermal and temperature guided beta-casein micellization were studied by dynamic light scattering, circular dichroism and Fourier transform infrared spectroscopy techniques. Micelle formation induced by the increase in the protein concentration at constant temperature is accompanied by the formation of a small number of additional peptide hydrogen bonds, preliminary assigned to the intraprotein beta-structure. The heating results in more pronounced but qualitatively different changes consisted in dehydration of the peptide groups and disruption of the polyproline II helix segments with the subsequent conversion to the random conformation and the beta-turns. Nevertheless, in both cases the total number of residues involved in the transition is very few and cannot be regarded as a decisive factor for casein micellization.     

Azospirillum brasilense colonisation of wheat roots and the role of lectin–carbohydrate interactions in bacterial adsorption and root-hair deformation

The dynamics of adsorption of the nitrogen-fixing soil bacteria Azospirillum brasilense 75 and 80 (isolated from soil samples collected in Saratov Oblast, southern Russia) and A. brasilense Sp245 to the roots of seedlings of common spring wheat was studied in relation to inoculum size, period of incubation with the roots and bacterial-growth phase. The number of root-attached cells increased with increasing size of inoculum and time of contact. The saturation of root-surface adsorption was observed by 24 h of co-incubation for A. brasilense 75, by 6 h for A. brasilense 80, and by 3 h for A. brasilense Sp245. The firmness of bacterial–root attachment increased after extended co-incubation. Differences in the adsorption kinetics of the azospirilla were found that were associated with bacterial-growth phases. Azospirilla attached to the roots of their host cultivar more actively than they did to the roots of a non-host cultivar. Adsorption was partially inhibited when the roots were treated with N-acetyl-D-glucosamine. Maximal inhibition occurred after a 3-h exposure of the roots to the bacteria. Root-hair deformation induced with polysaccharide-containing complexes from the Azospirillum capsular material was inhibited by N-acetyl-D-glucosamine and chitotriose, specific haptens of wheat germ agglutinin. A possible mechanism of the mutual influence of bacteria and plants may involve key roles of wheat germ agglutinin, present on the roots, and the polysaccharide-containing components of the Azospirillum capsule.     

Effect of flavonoids on the composition of surface glycopolymers of Azospirillum lipoferum Sp59b

Cultivation of the type strain Azospirillum lipoferum Sp59b in the presence of flavonoid quercetin induced modification of the structure of the bacterial lipopolysaccharide. Cultivation in the presence of the flavonoid was shown to result in altered serological characteristics of the bacteria, increased heterogeneity of the outer membrane lipopolysaccharide pool, as well as in modified composition and fatty acid ratio of lipid A. The flavonoid was shown to induce the synthesis of the O-specific polysaccharide with the repeating structure represented by a tetrasaccharide consisting of a linear trisaccharide fragment of α-L-Rhap residues in the main chain and the terminal β-D-Glcp residue. The structure of this O-specific polysaccharide was identical to the previously determined structure of the capsular polysaccharide of these bacteria grown without quercetin. Modifications in the structural composition of the capsular polysaccharide induced by cultivation in the presence of quercetin were revealed.     

Effect of Cultivation Conditions on the Composition of Extracellular Polysaccharide-Containing Substances in the Bacterium Azospirillum brasilense

Maintenance of pH 7.0 during the fermentation period favors accumulation of high molecular weight polysaccharide-containing components called lipopolysaccharide–protein and polysaccharide–lipid complexes in the capsules and culture medium. Increased pH of the culture medium to 8.0 reduced the period of exponential growth and the yield of polysaccharide-containing complexes as compared to optimal conditions. Maintenance of pH 5.5 suppressed the culture growth and polysaccharide production. The polysaccharide–lipid complexes obtained when pH was stabilized at the level of 7.0–8.0 had relatively low molecular weights and included only acidic polysaccharides. The use of potassium gluconate instead of sodium malate as a source of carbon in the culture medium changed the polysaccharide composition and increased the content of glucosamine, which increased the affinity of polysaccharides for wheat germ agglutinin. Prolongation of Azospirillum cultivation to five days introduced new glucose-containing polysaccharide components in the capsule.     

Participation of azospirillium polysaccharides in interaction with wheat root surface]

The present study was undertaken to comparatively investigate the attachment capacities of Azospirillum brasilense Sp245 and its lipopolysaccharide-defective Omegon-Km mutants KM018 and KM252, as well as their activities with respect to the alteration of the morphology of wheat seedling root hairs. The adsorption dynamics of the parent Sp245 and mutant KM252 strains of azospirilla on the seedling roots of the soft spring wheat cv. Saratovskaya 29 were similar; however, the attachment capacity of the mutant KM252 was lower than that of the parent strain throughout the incubation period (15 min to 48 h). The mutation led to a considerable decrease in the hydrophobicity of the Azospirillum cell surface. The lipopolysaccharides extracted from the outer membrane of A. brasilense Sp245 and mutant cells with hot phenol and purified by chromatographic methods were found to induce the deformation of the wheat seedling root hairs, the lipopolysaccharide of the parent strain being the most active in this respect. The role of the carbohydrate moiety of lipopolysaccharides in the interaction of Azospirillum cells with plants is discussed.     

Role of the clasping-leaved pondweed (Potamogeton perfoliatus) polysaccharides in formation of its bacterial environment

The effect of the polysaccharides of clasping-leaved pondweed (Potamogeton perfioliatus) on the formation of a bacteriocenosis of this plant was demonstrated by research on chemoreception, relative surface hydrophobicity, and the growth characteristics of the members of five bacterial genera abundant in this microbiocenosis. The plant heteropolysaccharides of anionic and cationic nature were found to participate in selective stimulation or inhibition of growth of some microbial groups in surrounding water. These findings improve our understanding of the spectrum of physiological activity of glycopolymers of diverse origin.     

Study of protective role of the polysaccharide-containing components of capsules of Azospirillum brasilense

The involvement of the carbohydrate components of the Azospirillum brasilense Sp245 capsules in bacterial protection from the action of extreme factors was investigated. The survival of encapsulated and non-encapsulated azospirilla exposed to elevated (46-48 degrees C) and below-freezing (-20 and -70 degrees C) temperatures, extreme pH values (2 and 10), and to drying was studied. High-molecular-weight carbohydrate-containing complexes (lipopolysaccharide-protein complex and polysaccharide-lipid complex) were isolated from the capsular material of azospirilla. It was shown that the addition of these complexes to the suspension of decapsulated cells before exposing them to extreme factors enhanced their survival rates by 15 to 51%.