The environmental transport and attachment behavior of pathogenic prion protein

Prions, the infectious agents in transmissible spongiform encephalopathies such as bovine spongiform encephalopathy and chronic wasting disease of deer and elk, represent a potential threat to human and wildlife health. Prions enter soil and subsurface environments through shedding, decomposition of carcasses, and disposal of infected waste. Understanding of prion fate and transport in soils and subsurface environments is extremely limited. This research furthered understanding of the behavior of prions in natural environments by quantifying the interactions of prion protein with environmentally relevant surfaces differing in physicochemical properties. Column transport experiments using soils spanning a range of textures and prions from two sources (purified preparations and protease-treated brain homogenate) showed that pathogenic prion protein exhibits limited mobility in most mineral. These data suggest that prions entering soil environments are retained at or near the surface where they are more likely to be consumed by grazing animals. The largest degree of prion penetration was observed in columns packed with quartz sand, although detectable amounts of prions were not observed in column effluent. Experiments using municipal solid waste showed small amounts of prion protein transport out of the columns. This suggests that porous media with larger pore sizes, such as municipal solid waste, may permit transport of prions. Thus, emplacement of prion-infected material in landfills requires careful design and construction of disposal cells to prevent migration of infectious agent. Quartz crystal microbalance with dissipation monitoring, optical waveguide lightmode spectrometry and atomic force microscopy experiments revealed that electrostatic forces dominate initial interaction of prions with charged mineral surfaces. Pathogenic prion protein possesses net negative charge over the pH range typical of environment systems. Prions attached rapidly to positively charged model mineral surfaces (alumina at pH < point of zero charge). Attachment to negatively charged silica was slow and limited. Prions released into soil and subsurface environments are expected to preferentially interact with positively charged mineral surfaces. Non-electrostatic forces appeared to contribute to attachment to surfaces with low charge density.