Fate of prions in soil: interactions of RecPrP with organic matter of soil aggregates as revealed by LTA-PAS

The contribution of soil organic matter (OM) to the adsorption of a recombinant prion protein (RecPrP) was studied in microcosm systems (soil aggregates from two different soils) before and after OM removal by low temperature ashing (LTA). The LTA 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 the aggregates were characterized by photoacustic Fourier-transform IR spectroscopy (PAS-FTIR). High affinity (H-type) adsorption isotherms were found with complete removal of RecPrP from solution for protein/soil ratios up to 1:62.5. OM removal from aggregates decreased the adsorbed RecPrP in amounts corresponding to 330-1000 microg mg(-1) of soil organic carbon (OC) indicating that native OM has specific adsorption capacity comparable and/or 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.