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.