Model Prion Protein adsorption on Native Organic Matter of Soil Aggregates.

The researches carried out on prions adsorption related to soil were generally focused on the soil as a whole or on selected inorganic or organic constituents with equilibrium batch techniques which can not take into account their spatial distribution and/or the relative interrelationships occurring in natural environment. In fact, the sorption processes in the "in situ" conditions are complex phenomena due only partly to the properties of single components but, due also to some "newly born" properties resulting from of the interaction among constituents. In this work the adsorption of a recombinant protein whose structure mimics the ovine prion (recPrP) was studied on native OM of undisturbed soil aggregates used as a simplified microcosm model system of soil at laboratory scale, and considered as individual adsorption system rather than the summation of single constituents. A Low-Temperature Ashing (LTA) by oxygen plasma has been applied to investigate the contribution of OM to the adsorption of a recPrP on soil aggregates from two different soils before and after OM removal by LTA. This technique allows a controlled removal of OM layer by layer, like a peeling of an onion skin, with minimal disturbance of the mineral matrix. Soil aggregates were selected as a representative model of the "in situ" conditions. Adsorption from batch vs percolation experiments were compared, and High affinity (H-Type) adsorption isotherms were found , with maximal sorption amounts indicating that native OM has specific adsorption capacity even superior to the mineral matrix. The coupled LTA-PAS-FTIR approach demonstrated that, albeit OM composition was homogeneous throughout the aggregates, its presence in the most external surfaces of the aggregates affects the diffusion dynamics of RecPrP within the aggregates during percolation by a "filtering out" effect.