S. Yu. Shchegolev

Atypical R-S dissociation in Azospirillum brasilense

It was found that atypical R–S dissociation in the type strain A. brasilense Sp7 is not accompanied by drastic changes in the polysaccharide moieties of bacterial lipopolysaccharides but is rather due to different contributions of two O-specific polysaccharides (found in both R and S dissociants) to the age-dependent architectonics of the cell surface.

Antigenic identity of the capsule lipopolysaccharides, exopolysaccharides, and O-specific polysaccharides in Azospirillum brasilense

The antigenic identity (and close values of electrophoretic mobility) of capsular polysaccharides, exopolysaccharides, and O-specific polysaccharides was revealed in the Azospirillum brasilense strains Sp7 and Sp245 by the immunodiffusion and immunoelectrophoretic methods. Together with the literature data on the identity of the monosaccharide composition of these polymers, this gives evidence of the absence of a specific capsular antigen in the bacteria studied. Thus, extracellular Azospirillum brasilense polysaccharides are likely to represent O-antigenic lipopolysaccharide fragments excreted by the bacteria into the culture medium, and their identification as a capsule or as an exopolysaccharide depends on the strength of the attachment of these polysaccharides to the cell surface.

Optical activity of solutions and films of chitosan acetate

The optical activity of solutions, oligomers, and films of chitosan acetate in a molecular weight (М) range of 660—640 000 g mol–1 was studied by the optical rotation dispersion method. Monotonic dispersion curves lying in the range of negative values of specific optical rotation [α] are observed for all samples in a wavelength range of 300—700 nm. The absolute value of [α] decreases as the degree of polymerization decreases for solutions of chitosan acetate. Three regions are observed on the dependence [α] = f(logМ): constant [α] values for solutions of highmolecular-weight chitosan samples, their relatively weak change for low-molecular-weight samples, and a sharp change for oligomers. The transition to the low-molecular-weight analog of the monomeric chitosan unit, d-glucosamine, is characterized by the inversion of the rotation sign as high positive values of [α] are attained. The nontrivial for high-molecular-weight compounds dependence [α] = f(logМ) was established for chitosan acetate films: the module of [α] of the films increases with a decrease in the degree of polymerization. It is shown that the module of optical activity of the studied samples is determined by the mobility of structural units of oligomer, polymer, or film. It is found by X-ray diffractometry that differences in optical activity of the solutions and films are due to restriction of the mobility of macromolecular segments during the formation of high-molecular-weight chitosan films and incomplete relaxation processes of film systems to the state of energetically favorable conformations.

The Electro-Optical Investigation of Suspensions of Escherichia coli K-12 Cells Metabolizing Glucose, Lactose, and Galactose

The electro-optical characteristics of suspensions of Escherichia coli K-12 cells metabolizing glucose, lactose, and galactose were studied by measuring the suspension turbidity as a function of cell alignment in an orienting electric field whose frequency was varied from 10 kHz to 10 MHz. In a frequency range of 10 kHz to 1 MHz, the orientational spectra of E. coli K-12 cells grown on glucose and lactose considerably changed after their incubation in the presence of the sugars. These changes likely reflect alterations in the polarizability of the cells induced by sugar metabolism.

Biochemical evaluation of the morphogenetic potential of wheat callus cells in vitro

Morphogenetic processes in immature embryos of wheat (Triticum aestivum L.) were investigated using a molecular marker for meristematic cells of cereals (proliferative antigen of meristem initial cells, PAIC). The used genetic model comprised a series of almost isogenic lines of wheat alternative by the alleles of dwarfing genes (RhtB1c, RhtB1b, and Rht14) and the original cv. Saratovskaya 29. The Rht genetic system was found to affect the level of PAIC in the wheat callus cells during callus formation and subsequent regeneration. We found differences in the level of PAIC at certain stages of culturing and a general trend of its content in the course of callus formation and secondary differentiation in the callus tissue. Possible role of PAIC as a marker of meristematic centers within the callus tissue and the prospect of its use in breeding as an additional criterion for estimation of morphogenetic ability of the newly produced lines of wheat are discussed.

Modification of cellulose acetates for preparing chiral sorbents

Modification of cellulose acetates via sorption-desorption of vapors of mesogenic solvents in which the polymer forms a lyotropic liquid crystal phase and of mixtures of these solvents with water leads to the formation of a new chiral structure of the polymeric sample. This is manifested in a significant change in the value and even sign of the specific optical rotation of the polysaccharide system. The sorbents based on cellulose acetates that have been modified by such treatment exhibit specific affinity for definite optical antipodes. When a racemic mixture of L- and D-isomers of amino acids is passed through this sorbent, it acts as a chiral filter owing to “steric recognition” of one of the enantiomers, so that the filtrate contains an optically pure product (isomer). The revealed effects served as a basis for the development of a new procedure for preparation of optically pure stereoisomers of chiral products.

The Effect of Ampicillin on the Electrophysical Properties of Escherichia coli Cells

The study of the effect of ampicillin on the electrophysical properties of Escherichia coli cells showed that this antibiotic influences the orientational spectra (OSs) of the ampicillin-susceptible E. coli strains K-12 and XL-1 within the frequency range 10–1000 kHz of the orienting electric field and does not affect the OSs of the ampicillin-resistant strains K-12(pUC-18) and XL-1(pHEN1). The change in the electrooptical signal of the ampicillin-susceptible cells was maximum at an ampicillin concentration of 50 µg/ml and did not depend on the exposure time. The conclusion is drawn that changes in the OSs of cells can be used to evaluate their resistance to ampicillin.

Serological Relationships of Azospirilla Revealed by Their Motility Patterns in the Presence of Antibodies to Lipopolysaccharides

Motility of the serologically different Azospirillum brasilense strains Sp245 (serogroup I) and Sp7 (serogroup II) was studied in the presence of antibodies to their lipopolysaccharides (LPS). A procedure was proposed in order to determine the motility patterns indicating the specificity of the interaction between the anti-LPS antibodies and bacteria. Analysis of the effect of such antibodies on motility of 25 strains (A. brasilense, A. lipoferum, A. irakense, and Azospirillum sp.) revealed bacteria exhibiting antigenic cross reactions with A. brasilense Sp7 or Sp245. The effect of anti-LPS antibodies on motility of azospirilla was in agreement with the results of immune agglutination analysis of bacterial cells and of immunodiffusion analysis of the LPS preparations. According to our results, strains Azospirillum sp. SR81 and A. brasilense SR14 should be included into serogroups I and II, respectively.

Optical-activity anisotropy of ordered phases in cellulose acetates

The optical activity of anisotropic solutions of cellulose diacetate in nitromethane and dimethyl sulfoxide and of diand triacetate films with vitrified ordered structure has been studied. The systems under study are characterized by high specific optical rotation [α], suggesting formation of a cholesteric mesophase. The value of [α] is found to depend on the angle of rotation of the samples relative to the direction of the polarization vector of an incident light beam in the plane perpendicular to this beam (the anisotropy of optical activity). This dependence (indicatrix) shows an irregular pattern and, when plotted in Cartesian coordinates, can be described with a distorted sinusoid. The data on the resolution of indicatrices into harmonic constituents and isolation of contributions due to isotropic components and anisotropic components, each of which is determined by the structural element with the corresponding asymmetry, are analyzed.

Changes in the Antigenic Properties of Azospirillum brasilense Lipopolysaccharide, Induced by Addition of Tris-(hydroxymethyl)-aminomethane into the Culture Medium

Addition of tris-(hydroxymethyl)-aminomethane (Tris) into the culture medium of Azospirillum brasilense sp245 changes the antigenic properties of the lipopolysaccharide (LPS) isolated from the external membrane of the bacteria. LPS preparations from the bacteria grown in the presence of Tris have been analyzed by immunodiffusion, using monospecific antibodies. The disappearance of the precipitation band corresponding to one of the two O-specific polysaccharides of the LPS (O-PS) and changes in the electrophoretic profile have been revealed. However, only minor differences in absorption spectra of products of O-PS1 reaction with phenol/sulfuric acid have been demonstrated between the bacteria grown under standard conditions and in the presence of Tris.