Effect of physical parameters on the in situ survival of Escherichia coli MC-6 in an estuarine environment.
(1/98)
Survival of Escherichia coli MC-6 of fecal origin in an estuarine environment as affected by time, water temperature, dissolved oxygen, salinity, and montmorillonite in diffusion chambers has been elucidated. Several in situ physical parameters were recorded simultaneously, and viable cell numbers were estimated. The survival of the bacteria varied seasonally. Montmorillonite addition extended the time needed for a 50% reduction of the viable cell population (t1/2) of cells by 40% over the t1/2 of cells in Rhode River water alone. The effect of this clay was not significantly greater between 50- to 1,000 mug/ml montmorillonite concentrations. In all experiments, the relationships among pairs of variables were studied by regression and correlation analysis. The slope between viable cell numbers and water temperatures increased about 50% for each 10 C increment in temperature and gave a correlation coefficient r = 0.617, significant at 95% confidence level. A similar correlation coefficient, r = 0.670, was obtained between water temperature and t1/2 of the initial cell population. In all experiments regressions were performed considering all variables after bacteria had been in the Rhode River environment for 3 days. Coefficient of multiple determination was estimated as R2 = 0.756. Approximately 75.6% of the variance of viable cell numbers can be explained by variation in water temperature, dissolved oxygen, and salinity. Simple correlation coefficients within the regression steps were also computed. Survival of bacteria was closely and negatively correlated with increasing water temperature (r = -0.717). It is suggested that water temperature is the most important factor in predicting fecal coliform survival from point and nonpoint sources in assessing water quality in an estuarine ecosystem. (+info)
Delivery of extraterrestrial amino acids to the primitive Earth. Exposure experiments in Earth orbit.
(2/98)
A large collection of micrometeorites has been recently extracted from Antarctic old blue ice. In the 50 to 100 micrometers size range, the carbonaceous micrometeorites represent 80% of the samples and contain 2% of carbon. They might have brought more carbon to the surface of the primitive Earth than that involved in the present surficial biomass. Amino acids such as "-amino isobutyric acid have been identified in these Antarctic micrometeorites. Enantiomeric excesses of L-amino acids have been detected in the Murchison meteorite. A large fraction of homochiral amino acids might have been delivered to the primitive Earth via meteorites and micrometeorites. Space technology in Earth orbit offers a unique opportunity to study the behaviour of amino acids required for the development of primitive life when they are exposed to space conditions, either free or associated with tiny mineral grains mimicking the micrometeorites. Our objectives are to demonstrate that porous mineral material protects amino acids in space from photolysis and racemization (the conversion of L-amino acids into a mixture of L- and D-molecules) and to test whether photosensitive amino acids derivatives can polymerize in mineral grains under space conditions. The results obtained in BIOPAN-1 and BIOPAN-2 exposure experiments on board unmanned satellite FOTON are presented. (+info)
Stability of respiratory syncytial virus in a new bentonite holding medium.
(3/98)
Stability of respiratory syncytial virus was determined in a new bentonite holding medium and compared with two other commonly used media. Eventual infectivity titers were similar with all three preparations. (+info)
Lucigenin chemiluminescence assay as an adjunctive tool for assessment of various stages of inflammation: a study of quiescent inflammatory cells.
(4/98)
A simple, fast, precise and biologically relevant toxicity assay for screening cytotoxicity of minerals would have distinct advantages due to its cost benefits and relative savings in time. Furthermore, a bioassay to differentiate acute and chronic in vivo pulmonary reactions could have potential value as predictors of fibrogenicity and pathogenicity. In this study we examined the potential use of lucigenin as a probe to evaluate the correlation between chemiluminescence (CL) generated by alveolar macrophages with the known cytotoxicity and patho genicity by conventional bioassays. In this study, we used small doses of dust (20 microg) to minimize cellular overload and to maintain homeostasis. Crystalline silica a highly fibrogenic dust was used as positive control and results are compared with those for bentonite, kaolin and talc. Among the three minerals compared with silica, bentonite was more reactive (27%) in CL assay and declined sharply compared to other minerals. This sudden decline in bentonite CL is caused by cytotoxicity leading to cell death. CL-induced by talc was comparable to silica and declines slowly. Kaolin on the other hand produced relatively a weaker (25%) CL compared to silica. Our data using relatively low doses of dust suggest that the CL assay may have a better predictive value in cytotoxicity evaluations compared to conventional toxicity assays. (+info)
Desorption techniques for determination of metals mobility in soils.
(5/98)
Three leaching techniques for assessment of fixed and mobile metal or radionuclides in soils are demonstrated on radiocaesium speciation. A new leaching technique based on the variation of the leaching solution volume to solid phase amount is proposed. It enables parallel treatment of large numbers of samples and, therefore, is suitable for a routine analysis of contaminant mobility in soils. As a leaching solution, 1 M ammonium acetate is proposed for caesium, but any other desorption solution harmonised with existing speciation schemes can be used. (+info)
Activity of free and clay-bound insecticidal proteins from Bacillus thuringiensis subsp. israelensis against the mosquito Culex pipiens.
(6/98)
Bacillus thuringiensis subsp. israelensis produces parasporal insecticidal crystal proteins (ICPs) that have larvicidal activity against some members of the order Diptera, such as blackflies and mosquitoes. Hydrolysis of the ICPs in the larval gut results in four major proteins with a molecular mass of 27, 65, 128, and 135 kDa. Toxicity is caused by synergistic interaction between the 25-kDa protein (proteolytic product of the 27-kDa protein) and one or more of the higher-molecular-mass proteins. Equilibrium adsorption of the proteins on the clay minerals montmorillonite and kaolinite, which are homoionic to various cations, was rapid (<30 min for maximal adsorption), increased with protein concentration and then reached a plateau (68 to 96% of the proteins was adsorbed), was significantly lower on kaolinite than on montmorillonite, and was not significantly affected by the valence of the cation to which the clays were homoionic. Binding of the toxins decreased as the pH was increased from 6 to 11, and there was 35 to 66% more binding in phosphate buffer at pH 6 than in distilled water at pH 6 or 7.2. Only 2 to 12% of the adsorbed proteins was desorbed by two washes with water; additional washings desorbed no more toxins, indicating that they were tightly bound. Formation of clay-toxin complexes did not alter the structure of the proteins, as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the equilibrium supernatants and desorption washes and by dot blot enzyme-linked immunosorbent assay of the complexes, which was confirmed by enhanced chemiluminescence Western blot analysis. Free and clay-bound toxins resulted in 85 to 100% mortality of the mosquito Culex pipiens. Persistence of the bound toxins in nonsterile water after 45 days was significantly greater (mortality of 63% +/- 12.7%) than that of the free toxins (mortality of 25% +/- 12.5%). (+info)
Non-enzymatic oligomerization of racemic adenosine 5'-phosphorimidazolide on Na(+)-montmorillonite.
(7/98)
In this study, we have investigated non-enzymatic oligomerization of an activated racemic mononucleotide in the presence of Na(+)-montmorillonite. Oligomers up to the decamer in length were formed by oligomerization reactions of activated D- and L-mononucleotides. Similarly, oligomerization of an activated racemic mononucleotide results in the formation of oligomers up to the octamer. These results suggest that montmorillonite catalysis is quite efficient for the oligomerization of racemic monomers, though it is somewhat less efficient than that of D- and L-monomers. (+info)
Effects of bentonite on wool growth and nitrogen metabolism in fauna-free and faunated sheep.
(8/98)
Two experiments were carried out with sheep that originated from a fauna-free flock and were fed a soybean meal-corn silage diet with or without a bentonite supplement. One-half of the sheep fed each diet in each experiment were faunated with a mixed population of ruminal protozoa, whereas the other half of the sheep remained fauna-free until the end of both experiments. Wool growth and daily gain were measured in Exp. 1. (eight rams per treatment), which lasted 110 d, and the metabolic effects in the rumen and intestinal tract of protozoa and dietary bentonite supplement were tested with cannulated wethers (four wethers per treatment) in Exp. 2. The results of Exp. 1 showed decreased wool growth (P less than .05) due to the presence of protozoa in the rumen. Dietary supplementation with bentonite partly offset the decreased wool growth in sheep with protozoa, but there were no effects of dietary bentonite and no protozoa x bentonite interaction (P greater than .05). Daily gain was decreased by the dietary bentonite (P less than .05) supplement but was not affected (P greater than .05) by the ruminal presence of protozoa. In Exp. 2, protozoa increased (P less than .01) the ruminal concentrations of ammonia and decreased (P less than .05) the acetic:propionic acid molar ratio. Fractionation of N in the duodenal digesta flowing from the stomach to the small intestine showed that protozoa decreased (P less than .05) the flow of nonammonia N and bacterial N, and there was a protozoa x bentonite interaction for these effects (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS) (+info)