Interactions of prion proteins with soil

Prions, are proteinaceous particles recognized as the agents of a class of neurodegenerative disorders, called transmissible spongiform encephalopathies (TSE), or prion diseases. Epidemiological data suggest that TSE-contaminated environments may serve as source of infectivity, but there is no information about adsorption of prions onto soil. We carried out experiments by mixing, healthy, or scrapie-infected hamster brains homogenates with three types of soil suspended in different buffers: (i) two saline buffers, i.e., phosphate buffer solution (PBS) and CaCl₂ solution; (ii) a mix of nondenaturing detergents, i.e., Triton X-100 and sodium deoxycholate (DOC) solution; (iii) a non-ionic detergent, i.e., lauryl maltoside; (iv) two anionic detergents, i.e., Sarkosyl or sodium dodecyl sulphate (SDS); and (v) a chaotropic agent, i.e., urea. The unbound prion proteins were detected in the supernatants (after centrifugation of soil suspension) by Western blotting. Results clearly demonstrate that both the no infectious (PrP^C) and infectious (PrP^Sc) forms are adsorbed by all soils. Only 1% sodium dodecylsulphate (SDS) partially impeded the association of PrP^C, but not that of PrP^Sc with the sandy loam soil. Agents with different interacting properties towards hydrophilic and/or hydrophobic domains failed to extract PrP^Sc from sediments of soil-brain homogenate mixtures. The strong interaction of PrP^Sc with soil favors the accumulation of prions in soils, especially if amended with prion-containing organic fertilizers and/or whenever TSE-affected animal carcasses, placenta, and excreta in general are buried or laid at the soil surface.     

A simple gas chromatographic approach to evaluate CO2 release,N2O evolution,and O2 uptake from soil

Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO₂ evolution and O₂ uptake increased significantly. Positive relationships were found between the evolution of N₂O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO₂:O₂ ratio. The results given by this method show high reproducibility.     

Use of 0·1 m pyrophosphate to extract urease from a podzol

Sodium pyrophosphatc (0·1 m) at pH 7.1 and 37°C extracted a significant fraction of urease from a podzol. Maximum extraction values were obtained after 18 h. The yields of soil organic matter and urease activity during the extraction show a different pattern: the extraction of non-specific organic matter precedes and may facilitate the following extraction of an active urease organo-complex. The urease extracted by pyrophosphate is about 30 40 per cent of the total urease activity, as shown by plotting the urease activity against the population changes of ureolytic microorganisms, both in the original and extracted soil. The number of ureolytic microorganisms is unaffected by pyrophosphate, and the extracted urease is assumed to be extracellular.     

Fractionation of humus-urease complexes

Some techniques commonly used for enzyme purification were unsuitable to purify urease extracted by pyrophosphate from soil. An all-or-none behaviour seemed to be a prominent feature of such experiments but in some instances slight increases of specific activity were observed.The most effective purification of soil urease was achieved by exhaustively ultrafiltrating the soil extract against 0.1 m pyrophosphate at pH 7.1, separating the retained material into fractions of mol. wt. higher (A_I) and lower (A_II) than 10⁵, followed by gel chromatography.Increases in total activities were observed both after ultrafiltration and gel chromatography. Ultra-filtration increased the total activity of the extracted urease by about 8%. The specific activity of fraction A_I increased four fold, that of fraction A_II by more than three fold. Fractions obtained by gel chromatography accounted in toto for only 13.5% of the organic-C of the soil extract. Total urease activity increased by 45.6%. Specific activities increased to 6.9–18 times that of the soil extract.     

Effect of peroxidation on soil electrochemical properties

Treatment with hydrogen peroxide to destroy the organic matter shifts the surface charge towards positive values. This is in agreement with the suggestion that per oxidation produces artefacts in the soil residues, since metals released from organic matter precipitate as hydroxide coating and produce positively charged surfaces. In the presence of 0.1 M sodium pyrophosphate, treatment with hydrogen peroxide always shifts the surface charge towards negative values, notwithstanding the removal of the electronegative organic components. It is suggested that the bulk of electropositive iron and aluminium oxides in soil are associated with the organic matter and removed by the treatment, so that permanent negative charges of clay minerals dominate in soil residue.     

Characterization of Organic Matter in Compost Produced with Municipal Solid Wastes: An Italian Approach

Stabilization of the organic matter of a static pile of compost from municipal solid wastes (MSW) under a forced-pressure ventilation composting system was followed for 55 days during winter season. The materials were analyzed according to the official methodologies required by Italian regulations regarding the quality of composts from MSW. The stabilization process of the organic matter was monitored using both the degree of humification (DH), i.e. the ratio between the humified fractions (HA + FA) and the total extractable carbon (TEC), and the electrofocusing technique (EF). The DH increased steadily in compost during stabilization process and converged asymptotically at the end of the period of composting. The EF analyses of the organic extracts of compost from MSW showed a definite trend in the humification process and confirmed the actual evolution of the organic matter composted.     

Anomalous contents of heavy metals in soils and vegetation of a mine area in S.W. Sardinia,Italy

Samples of soils and vegetation from the mining area of South-West Sardinia (Italy) were analyzed for Pb, Zn, Cd, and Cu content. The area (more than 100 km²) is inhabited by many thousands of people; land utilization includes mainly grapes on some small plains and permanent sheep pasture on the hills. The levels of Pb, Zn, and Cd were found to be exceptionally high in most samples. Lead concentration was up to 71000 μg g^?1 in the soils and 4000 jig g^?1 in vegetation; Cd concentration was found up to 665 μg g^?1 in soils and 26.5 μg g^?1 in vegetation. The heavy metal content of some soil samples was highly variable. Data show that Pb is easily absorbed by plant roots and translocated to foliage. In spite of the high heavy metal level, no signs of toxicity were apparent in vegetation.     

Influence of metals on solubility of soil organic matter

Treatment of the alkali-soluble organic matter of soil with a cation-exchange resin resin (Amberlite IR 120, H⁺ form) strongly modified the solubility characteristics of the organic matter, even though only part of the metals was removed. Two or more types of sorption sites were involved in the binding of metals by soil organic matter. The Amberlite removable metals interfered with the separation of humic from fulvic acid.     

Stability and kinetic properties of humus-urease complexes

We have determined the kinetics and stabilities of various humus-urease preparations, extracted and purified from soil (Ceccanti, Nannipieri, Cervelli and Sequi, 1977). K_m, values of five different fractions in phosphate buffer ranged from 8 to 40 mM and were similar to those of urease extracted from various other sources. However, the optimal pH for urease activity of the soil fractions ranged from 7.5 to 8.8, in contrast to a pH optimum of about 7.0 for urease from sources other than soil. The shift in the optimal pH towards the alkaline region may be due to the influence of the negative charge of the humus matrix localized around the enzyme.Urease organo-complexes of mol. wt. < 10⁵ were slightly more resistant to thermal denaturation and to proteolysis than free urease. However, complexes of mol. wt. > 10⁵ were even more resistant, due probably to the occurrence of molecular arrangements similar to that proposed by Burns, El-Sayed and McLaren (1972a) and Burns, Pukite and McLaren (1972b). Thus although each of the five urease-active organic matter fractions exhibited different characteristics, they could be grouped into two distinct classes, according to mol. wt. and resistance to thermal denaturation and proteolysis.