Secondary immune response to flagellin conjugates with polyacrylic acid

The conditions of the activation of immunological memory by means of flagellin and its conjugate with polyacrylic acid (PAA) have been studied. The flagellin-PAA conjugate has proved to be capable of inducing the appearance of memory cells when introduced in doses, considerably lower (0.01 and 0.001 micrograms) than those of native protein (0.1, 1 and 10 micrograms). At the same time no manifest differences in the reactivation of flagellin-induced and conjugate-induced memory cells by the antigen have been established. Immunization with protein, as well as with its conjugate, has been found to induce the formation of mainly anti-Hi : 1,2 IgG in secondary immune response.     

Age-Related Dynamics of Discrimination of the Orientation of Rectangular Gratings at the Resolution Limit of the Visual System

The visual acuity of 215 observers between the ages of 3 and 20 years was measured by determining the minimal size of rectangular gratings, when the observer could discriminate horizontal and vertical gratings. The study of the influence of similar surrounding patterns on the assessment of visual acuity was conducted in parallel. The visual acuity was shown to increase with age and to reach the level typical of adults at about 11 years. All the observers had impaired discrimination of the orientation of gratings when the surrounding gratings were arranged close to each other. The distances at which the impairment occurs gradually decrease with increasing age up to 20 years from 2.75 to 1.5–0.75 periods of the test frequency. The problem of the formation in ontogenesis of possible mechanisms ensuring visual acuity and the ability to perform the task of objects' segmentation from the surrounding is discussed.     

Physical,chemical, and regulatory properties of glycolate oxidase in C<Subscript>3</Subscript> and C<Subscript>4</Subscript> plants

Physical, chemical, and regulatory properties of glycolate oxidase (GO) isolated from the leaves of C₄ and C₃ plants (Zea mays L., cv. Voronezhskaya 76 and Glycine max (L.) Merr., cv. Pripyat’, respectively) were studied. The homogenous preparations were obtained by multistage enzyme purification from soybean leaves and maize mesophyll and bundle sheath. The glycolate oxidase (GO) preparations obtained consisted of two types of subunits, 37 and 44 kD. The GO isolated from C₃ plant leaves had many in common with that extracted from C₄ plant bundle sheath as regards physical, chemical, and catalytic properties. The primary function of GO in both plant types is metabolism of glycolate, which is a product of ribulosebisphosphate oxalacetic acid oxidation and is used by plants for biosynthesis of hydrocarbons and amino acids.     

Electron transfer through the acceptor side of photosystem I: Interaction with exogenous acceptors and molecular oxygen

This review considers the state-of-the-art on mechanisms and alternative pathways of electron transfer in photosynthetic electron transport chains of chloroplasts and cyanobacteria. The mechanisms of electron transport control between photosystems (PS) I and II and the Calvin–Benson cycle are considered. The redistribution of electron fluxes between the noncyclic, cyclic, and pseudocyclic pathways plays an important role in the regulation of photosynthesis. Mathematical modeling of light-induced electron transport processes is considered. Particular attention is given to the electron transfer reactions on the acceptor side of PS I and to interactions of PS I with exogenous acceptors, including molecular oxygen. A kinetic model of PS I and its interaction with exogenous electron acceptors has been developed. This model is based on experimental kinetics of charge recombination in isolated PS I. Kinetic and thermodynamic parameters of the electron transfer reactions in PS I are scrutinized. The free energies of electron transfer between quinone acceptors A_1A/A_1B in the symmetric redox cofactor branches of PS I and iron–sulfur clusters F_X, F_A, and F_B have been estimated. The second-order rate constants of electron transfer from PS I to external acceptors have been determined. The data suggest that byproduct formation of superoxide radical in PS I due to the reduction of molecular oxygen in the A1 site (Mehler reaction) can exceed 0.3% of the total electron flux in PS I.     

Manure-amended soil characteristics affecting the survival of E. coli O157:H7 in 36 Dutch soils

The recent increase in foodborne disease associated with the consumption of fresh vegetables stresses the importance of the development of intervention strategies that minimize the risk of preharvest contamination. To identify risk factors for Escherichia coli O157:H7 persistence in soil, we studied the survival of a Shiga-toxin-deficient mutant in a set of 36 Dutch arable manure-amended soils (organic/conventional, sand/loam) and measured an array of biotic and abiotic manure-amended soil characteristics. The Weibull model, which is the cumulative form of the underlying distribution of individual inactivation kinetics, proved to be a suitable model for describing the decline of E. coli O157:H7. The survival curves generally showed a concave curvature, indicating changes in biological stress over time. The calculated time to reach the detection limit ttd ranged from 54 to 105 days, and the variability followed a logistic distribution. Due to large variation among soils of each management type, no differences were observed between organic and conventional soils. Although the initial decline was faster in sandy soils, no significant differences were observed in ttd between both sandy and loamy soils. With sandy, loamy and conventional soils, the variation in ttd was best explained by the level of dissolved organic carbon per unit biomass carbon DOC/biomC, with prolonged survival at increasing DOC/biomC. With organic soils, the variation in ttd was best explained by the level of dissolved organic nitrogen (positive relation) and the microbial species diversity as determined by denaturing gradient gel electrophoresis (negative relation). Survival increased with a field history of low-quality manure (artificial fertilizer and slurry) compared with high-quality manure application (farmyard manure and compost). We conclude that E. coli O157:H7 populations decline faster under more oligotrophic soil conditions, which can be achieved by the use of organic fertilizer with a relatively high C/N ratio and consequently a relatively low rate of nutrient release.     

Wave-like Distribution Patterns of <Emphasis Type="Italic">Gfp</Emphasis>-marked <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> Along Roots of Wheat Plants Grown in Two Soils

Culturable rhizosphere bacterial communities had been shown to exhibit wave-like distribution patterns along wheat roots. In the current work we show, for the first time, significant wave-like oscillations of an individual bacterial strain, the biocontrol agent Pseudomonas fluorescens 32 marked with gfp, along 3-week-old wheat roots in a conventionally managed and an organically managed soil. Significant wave-like fluctuations were observed for colony forming units (CFUs) on selective media and direct fluorescent counts under the microscope. Densities of fluorescent cells and of CFUs fluctuated in a similar manner along wheat roots in the conventional soil. The frequencies of the first, second, and third harmonics were similar for direct cell counts and CFUs. Survival of P. fluorescens 32-gfp introduced into organically managed soil was lower than that of the same strain added to conventionally managed soil. Thus, when root tips reached a depth of 10–35 cm below soil level, the majority of the introduced cells may have died, so that no cells or CFU”s were detected in this region at the time of sampling. As a result, significant waves in CFUs or direct counts along roots were not found in organically managed soil, except when a sufficiently long series with detectable CFUs were obtained. In this last case the wave-like fluctuation in CFUs was damped toward the root tip. In conclusion, when cells of a single bacterial strain randomly mixed in soil survived until a root tip passed, growth and death cycles after passage of the root tip resulted in oscillating patterns of population densities of this strain along 3-week-old wheat roots.     

Physicochemical and biological factors affecting atmospheric methane oxidation in gray forest soils

The decline of methane oxidizing activities in gray forest soil upon its conversion into arable land was shown to be caused by major changes in biotic and physicochemical properties of soil. Using the method of immune serums, methane-oxidizing bacteria were detected in both forest and agricultural soils, but their populations differed significantly in both abundance and composition. In the forest soil, the number of methanotrophs was an order of magnitude higher than in arable soil, amounting to 3.5 × 10⁸ and 0.24 × 10⁸ cells/g soil, respectively. All methane-oxidizing bacteria identified in the forest soil belonged to the genus Methylocystis, and 94% of these were represented by a single species, M. parvus. The arable soil was dominated by type I methanotrophs (Methylobacter and Methylomonas, 67.6%), occurring along with bacteria of the genus Methylocystis. In addition, arable soil is characterized by a low content of microbial biomass, lower porosity and water resistance of soil aggregates, and the predominance of nitrogen mineralization processes over those of nitrogen immobilization. These factors can also contribute to lower rates of methane oxidation in arable soil as compared to forest soil.__________Translated from Mikrobiologiya, Vol. 74, No. 2, 2005, pp. 255–260.Original Russian Text Copyright © 2005 by Kravchenko, Semenov, Kuznetsova, Bykova, Dulov, Pardini, Gispert, Boeckx, Cleemput, Galchenko.     

An approach to balancing the positive and negative effects of elevated nitrogen oxides in the lower atmosphere on terrestrial plants

Elevated NOx in the lower atmosphere has three major effects on terrestrial plants. On the one hand, it causes an increase in surface ozone concentration. This reduces plant growth rate. On the other hand, elevated NOx causes an increase in the flux of oxidized N compounds from the atmosphere to the land surface. This plays a dual role in the life of terrestrial plants. Additional N in soils stimulates plant growth (N-fertilization effect), whereas soil acidification may negatively affect plants. A simple empirical model for calculating the overall effect of anthropogenic increase in NOx level has been developed. The model is based on experimental "cause-response" data presented in world scientific literature. Calculations showed that at the large scale, among the above-mentioned changes, elevated O3 plays a major and negative role in plant life. Its negative effect on plants is partly compensated by N fertilization in unmanaged ecosystems. Such compensation appears to be negligible in agricultural lands. There are vast territories in Euro--Asia--for instance, a territory of Russia--in which acid atmospheric deposition has no significant effect on terrestrial plants.     

Thermodynamic models, describing formation of "bridges" between nucleic acid molecules and liquid crystals

Three variants of the model for the formation of "bridges" between the nucleic acid molecules fixed in the structure of particles of liquid-crystalline dispersions were considered. What the three variants have in common is that the bridges represent polymeric chelate cross-links consisting of alternating molecules of daunomycin and copper ions. The differences between the three variants are that in the first variant, the bridges begin and end with daunomycin molecules that form a complex by the mechanism of external binding with nucleic acids; in the second variant, the bridges begin and end with copper ions coupled with the pairs of bases of nucleic acids; and in the third variant, the bridges begin with the daunomycin molecule and end with the copper ion. For each variant, a mathematical model was constructed, which describes the formation of bridges, and equations of binding were derived. The results of calculations were compared with the experimental data. Within the framework of each variant, the values of the energy of interaction between the daunomycin molecule and the copper ion in the bridge, the energy of interaction of the daunomycin molecule with the nucleic acid, and the length of the bridge were varied. For all variants, those values of the parameters were chosen that fit best the experimental data. The theoretical curves obtained using the three variants of the model agree rather well with the family of experimental curves. The best agreement between the theoretical and experimental data was obtained when the polymeric chelate bridge includes more than two daunomycin molecules.