Electrooptical parameters of kanamycin-treated <Emphasis Type="Italic">E. coli</Emphasis> cell suspensions

The effect of kanamycin on the electrophysical parameters of cell suspensions of Escherichia coli K-12 and pMMB33 was investigated. Incubation of the sensitive K-12 strain with kanamycin resulted in significant changes in the orientation spectra (OS) of the cell suspensions; these changes were not revealed in the case of the resistant pMMB33 strain. In the case of the sensitive K-12 strain incubated with different kanamycin concentrations, changes in the OS of the cell suspensions occurred within the 10–1000 kHz frequency range of the orienting electrical field. The most pronounced change in the electrooptical signal was observed at 10 μg/ml of kanamycin. Control experiments were carried out by standard plating on nutrient media. Thus, the OS changes of suspensions in the presence of antibiotics may be used as a test for microbial resistance to such antibiotics.     

An acoustic method for the analysis of bacterial cells

The application of a biological electroacoustic sensor based on a lateral electric-field-excited piezoelectric resonator for the study of bacterial cells that interact with specific bacteriophages, mini-antibodies, and polyclonal antibodies was successfully demonstrated. The determined lower limit of microbialcell detection was approximately of 10³ to 10⁴ cells/mL for the duration of the assay of 10 min. The possibility of bacterial-cell detection via interaction with specific agents in the presence of extraneous microbiota was shown. The method allowed us to determine the spectrum of lytic activity of bacteriophages and the sensitivity of microbial cells to bacteriophages. The results of the study showed that application of a sensor piezoelectric lateral-field resonator is a promising technique for the detection and identification of microbial cells and determination of their phage resistance in microbiology, medicine, and veterinary medicine. Furthermore, the results of the experiments made it possible to understand the mechanisms of the processes that occur in a suspension of bacterial cells in the presence of various biological agents. The method also may provide useful information regarding biophysical mechanisms of interactions that occur in microbial populations.     

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.     

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.     

Determination of the Structure of the Repeated Unit of the Azospirillum brasilense SR75 O-Specific Polysaccharide and Homology of the lps Loci in the Plasmids of Azospirillum brasilense strains SR75 and Sp245

The structural identity of the repeated unit in O-specific polysaccharides (OPSs) present in the outer membrane of strain SR75 of the bacterium Azospirillum brasilense, isolated from wheat rhizosphere in Saratov oblast, and the previously studied OPSs of A. brasilense strain Sp245, isolated from surfacesterilized wheat roots in Brazil, has been demonstrated. Plasmid profiles, DNA restriction, and hybridization assays suggested that A. brasilense strains SR75 and Sp245 have different genomic structures. It was shown that homologous lps loci of both strains were localized in their plasmid DNA. This fact allows us to state that, despite their different origin, the development of the strains studied was convergent. Presumably, the habitation of these bacteria in similar ecological niches influenced this process in many respects. __________ Translated from Mikrobiologiya, Vol. 74, No. 5, 2005, pp. 626–632. Original Russian Text Copyright ? 2005 by Fedonenko, Borisov, O. Konnova, Zdorovenko, Katsy, S. Konnova, Ignatov.     

A new approach to enhance PCR specificity

A new approach to enhanced specificity and product yield of polymerase chain reaction is proposed. It is based on control of DNA polymerase activity during PCR by changing the magnesium ion concentration, which depends on the temperature of the reaction mixture. A slightly soluble magnesium salt, magnesium oxalate, whose solubility depends on temperature, was used as a source of magnesium ions. During PCR, magnesium oxalate was maintained at saturating concentration by the presence of an insoluble excess of this salt, and the concentration of magnesium ions depended on the salt solubility: binding of magnesium ions at lower temperatures and their release at higher temperatures was shown to affect the DNA polymerase activity and to favor the specific PCR amplification of the target DNA fragment.     

Determination of organophosphorus aromatic nitro insecticides and p-nitrophenol by microbial-cell respiratory activity

We examined the possibility of measuring the organophosphorus aromatic nitro insecticides metaphos and sumithion as well as their hydrolysis product p-nitrophenol (PNP) by the specific respiratory activity (SRA) of Pseudomonas putida C-11, P. putida BA-11, and Acinetobacter calcoaceticum A-122. The plots of cellular SRA against the two insecticides and PNP were linear over the ranges of 0.5-2.5 microM for P. putida C-11 and BA-11 and 0.5-1.0 microM for A. calcoaceticum A-122. P. putida BA-11 showed the greatest respiratory-response selectivity in the determination of the test substrates. We made comparison studies of the SRA of cells immobilised by two methods: carrier-surface adsorption and inclusion in various gels. We discuss the feasibility of developing a microbial sensor system for the determination of metaphos, sumithion, and PNP in aqueous media.     

Chemical composition and immunochemical characteristics of the lipopolysaccharide of nitrogen-fixing rhizobacterium Azospirillum brasilense CD

The chemical composition of the lipopolysaccharide of the associative diazotrophic rhizobacterium Azospirillum brasilense Cd has been studied. Among the main components of the hydrophobic part of the lipopolysaccharide, we identified 3-hydroxytetradecanoic, hexadecenoic, 3-hydroxyhexadecanoic, hexadecanoic, octadecenoic, and nanodecanoic fatty acids; the carbohydrate part contained rhamnose, galactose, and mannose. Polyclonal antibodies against the preparation under study were raised in rabbits. Serological relations between A. brasilense Cd and other strains of Azospirillum spp. were studied using double radial immunodiffusion and enzyme-linked immunosorbent assay.