Irina V. Yegorenkova

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.

Biofilm Formation by Paenibacillus polymyxa Strains Differing in the Production and Rheological Properties of Their Exopolysaccharides

We evaluated the ability of several strains of the rhizobacterium Paenibacillus polymyxa, differing in the yield and rheological properties of their exopolysaccharides, to form biofilms on abiotic surfaces. Of these strains, P. polymyxa 1465, giving the highest yield of extracellular polysaccharides and the highest kinematic viscosity of the culture liquid and of aqueous polysaccharide solutions, proved to be the most active in forming biofilms on hydrophobic and hydrophilic surfaces. Enzyme-linked immunosorbent assay with rabbit polyclonal antibodies developed to isolated exopolysaccharides of P. polymyxa 1465 and 92 was used to detect P. polymyxa’s polysaccharidic determinants in the composition of the biofilm materials.

Paenibacillus polymyxa rhizobacteria and their synthesized exoglycans in interaction with wheat roots: colonization and root hair deformation.

We examined the ability of several Paenibacillus polymyxa strains to colonize wheat roots and the ability of P. polymyxa exoglycans to induce root hair deformation. For the first time, exopolysaccharides isolated from P. polymyxa were found to produce, with different intensities, various morphological changes in the root hairs of wheat seedlings, which are some of the earliest responses of plants to bacteria in the surrounding milieu. P. polymyxa 1465, giving the highest exopolysaccharide yield and the highest viscosity of aqueous exopolysaccharide solutions, was best able to colonize wheat seedling roots, and its exopolysaccharide proved to be the best in producing root hair deformation. It is suggested that P. polymyxa exoglycans have an active role in the establishment of plant–microbe associations.

Use of ELISA with Antiexopolysaccharide Antibodies to Evaluate Wheat-Root Colonization by the Rhizobacterium Paenibacillus polymyxa

Enzyme-linked immunosorbent assay with rabbit polyclonal antibodies developed to isolated exopolysaccharide of Paenibacillus polymyxa 1465 was used to evaluate the colonization of wheat-seedling roots by this bacterium. The assay conditions were optimized for detection of the P. polymyxa exopolysaccharide determinants forming part of the samples used (homogenates of inoculated roots). The dynamics of the immunoenzymatic revealing of specific polysaccharidic antigenic determinants in the samples’ composition correlated with an increase in P. polymyxa numbers on the roots found by estimation of colony-forming units.

Composition and Immunochemical Characteristics of Exopolysaccharides from the Rhizobacterium Paenibacillus polymyxa 1465

Exopolysaccharides (EPS) synthesized by Paenibacillus polymyxa 1465 in the course of batch cultivation were proven to contain neutral and acidic fractions. EPS are heterogeneous polysaccharides, represented by a complex of macromolecules with molecular mass of 7 × 104 to 2 × 106 Da. The acidic component was shown to be predominant in EPS preparations isolated from bacteria cultivated on glucose, which corresponds to a higher viscosity of EPS water solutions. The exoglycans were shown to contain glucose, mannose, galactose, and uronic acids. Polyclonal rabbit antibodies against the isolated P. polymyxa 1465 EPS preparations were used in a comparative immunodiffusion analysis of a number of P. polymyxa strains.

Exopolysaccharides of Paenibacillus polymyxa Rhizobacteria in Plant–Bacterial Interactions

Paenibacillus polymyxa (formerly known as Bacillus polymyxa), a nonpathogenic endospore-forming rhizobacterium, is one of the most industrially interesting facultative anaerobes. It is an active producer of various biologically active substances, including exopolysaccharides, which possess a range of unique properties. This chapter outlines the present state of research on P. polymyxa bacteria, their ecology and biotechnological potential, and the mechanisms of their stimulatory effect on plants. Special emphasis is placed on the structural–functional characterization of P. polymyxa exoglycans and on their important role in the establishment of plant–microbe associations.

Immunomodulatory activity of exopolysaccharide from the rhizobacterium Paenibacillus polymyxa CCM 1465

Bacterial polysaccharides are promising stimulants of protective functions in humans and animals. We investigated the ability of exopolysaccharide from the rhizobacterium Paenibacillus polymyxa CCM 1465 to induce nonspecific resistance factors in the macroorganism. We examined in vitro the effect of the exopolysaccharide, produced with different carbon sources, on the phagocytic activity of murine macrophages, on the generation of reactive oxygen species and of enzymes (acid phosphatase and myeloperoxidase), on the proliferation of murine splenocytes, and on the synthesis of proinflammatory cytokines [interleukin-1 (IL-1) and tumor necrosis factor α (TNF-α)] by human mononuclear cells. The exopolysaccharide promoted the phagocytosis of bacterial cells, activated metabolic processes in human and animal leukocytes, and moderately affected the production of TNF-α and IL-1β. The exopolysaccharides produced on media with glucose and sucrose differed in their effect on the immune cells, possibly owing to their different compositions, structures, and properties. The results validly indicate that the exopolysaccharide of P. polymyxa CCM 1465 promotes nonspecific immunity. Therefore, it can find application as a biologically active immunomodulatory substance.