Adsorption of pathogenic prion protein to quartz sand

Biodegradation of bovine spongiform encephalopathy prions in compost

To reduce the transmission risk of bovine spongiform encephalopathy prions (PrPBSE), specified risk materials (SRM) that can harbour PrPBSE are prevented from entering the feed and food chains. As composting is one approach to disposing of SRM, we investigated the inactivation of PrPBSE in lab-scale composters over 28 days and in bin composters over 106-120 days. Lab-scale composting was conducted using 45 kg of feedlot manure with and without chicken feathers. Based on protein misfolding cyclic amplification (PMCA), after 28 days of composting, PrPBSE seeding activity was reduced by 3-4 log10 with feathers and 3 log10 without. Bin composters were constructed using ~ 2200 kg feedlot manure and repeated in 2017 and 2018. PMCA results showed that seeding activity of PrPBSE was reduced by 1-2 log10 in the centre, but only by 1 log10 in the bottom of bin composters. Subsequent assessment by transgenic (Tgbov XV) mouse bioassay confirmed a similar reduction in PrPBSE infectivity. Enrichment for proteolytic microorganisms through the addition of feathers to compost could enhance PrPBSE degradation. In addition to temperature, other factors including varying concentrations of PrPBSE and the nature of proteolytic microbial populations may be responsible for differential degradation of PrPBSE during composting.

Chemical Inactivation of Prions Is Altered by Binding to the Soil Mineral Montmorillonite

Environmental routes of transmission contribute to the spread of the prion diseases chronic wasting disease of deer and elk and scrapie of sheep and goats. Prions can persist in soils and other environmental matrices and remain infectious for years. Prions bind avidly to the common soil mineral montmorillonite, and such binding can dramatically increase oral disease transmission. Decontamination of soil in captive facilities and natural habitats requires inactivation agents that are effective when prions are bound to soil microparticles. Here, we investigate the inactivation of free and montmorillonite-bound prions with sodium hydroxide, acidic pH, Environ LpH, and sodium hypochlorite. Immunoblotting and bioassays confirm that sodium hydroxide and sodium hypochlorite are effective for prion deactivation, although montmorillonite appears to reduce the efficacy of hypochlorite. Acidic conditions slightly reduce prion infectivity, and the acidic phenolic disinfectant Environ LpH produces slight reductions in infectivity and immunoreactivity. The extent to which the association with montmorillonite protects prions from chemical inactivation appears influenced by the effect of chemical agents on the clay structure and surface pH. When clay morphology remains relatively unaltered, as when exposed to hypochlorite, montmorillonite-bound prions appear to be protected from inactivation. In contrast, when the clay structure is substantially transformed, as when exposed to high concentrations of sodium hydroxide, the attachment to montmorillonite does not slow degradation. A reduction in surface pH appears to cause slight disruptions in clay structure, which enhances degradation under these conditions. We expect our findings will aid the development of remediation approaches for successful decontamination of prion-contaminated sites.

Influence of humic acid on transport, deposition and activity of lysozyme in quartz sand

Interaction with natural organic matter (NOM) is hypothesized to impact the fate and bioavailability of enzymes and some hazardous proteins in terrestrial and aquatic environments. By using saturated column transport experiments the transport and deposition of the model enzyme lysozyme (LSZ), in the absence and presence of purified Aldrich humic acid (PAHA), was investigated at a series of mass ratios PAHA/LSZ at pH 5 and 8 and two ionic strength values (0.5 mM and 50 mM KCl solution). PAHA decreased LSZ transport under all conditions. The shapes of breakthrough curves (BTCs) and retention profiles (RPs) during cotransport of both colloids evolved from symmetrical to blocking with time and from flat to hyper-exponential with depth, respectively, in response to increases in mass ratio PAHA/LSZ. The results indicated that the "size-selective retention" and concurrent homo- and hetero-aggregation induced straining, which resulted in preferential retention of relatively large PAHA-LSZ aggregates in the column and elution of relatively small ones. Due to differences in aggregate size, in general, the enzyme activity of LSZ in the effluent was larger and that of the retained LSZ was smaller than that of the influent. Therefore, protein transport process could partially increase the enzyme activity and bring potential environmental hazards.

Clay content and pH: soil characteristic associations with the persistent presence of chronic wasting disease in northern Illinois

Environmental reservoirs are important to infectious disease transmission and persistence, but empirical analyses are relatively few. The natural environment is a reservoir for prions that cause chronic wasting disease (CWD) and influences the risk of transmission to susceptible cervids. Soil is one environmental component demonstrated to affect prion infectivity and persistence. Here we provide the first landscape predictive model for CWD based solely on soil characteristics. We built a boosted regression tree model to predict the probability of the persistent presence of CWD in a region of northern Illinois using CWD surveillance in deer and soils data. We evaluated the outcome for possible pathways by which soil characteristics may increase the probability of CWD transmission via environmental contamination. Soil clay content and pH were the most important predictive soil characteristics of the persistent presence of CWD. The results suggest that exposure to prions in the environment is greater where percent clay is less than 18% and soil pH is greater than 6.6. These characteristics could alter availability of prions immobilized in soil and contribute to the environmental risk factors involved in the epidemiological complexity of CWD infection in natural populations of white-tailed deer.

Peroxymonosulfate Rapidly Inactivates the Disease-Associated Prion Protein

Prions, the etiological agents in transmissible spongiform encephalopathies, exhibit remarkable resistance to most methods of inactivation that are effective against conventional pathogens. Prions are composed of pathogenic conformers of the prion protein (PrP(TSE)). Some prion diseases are transmitted, in part, through environmental routes. The recalcitrance of prions to inactivation may lead to a persistent reservoir of infectivity that contributes to the environmental maintenance of epizootics. At present, few methods exist to remediate prion-contaminated land surfaces. Here we conducted a proof-of-principle study to examine the ability of peroxymonosulfate to degrade PrP(TSE). We find that peroxymonosulfate rapidly degrades PrP(TSE) from two species. Transition-metal-catalyzed decomposition of peroxymonosulfate to produce sulfate radicals appears to enhance degradation. We further demonstrate that exposure to peroxymonosulfate significantly reduced PrP(C) to PrP(TSE) converting ability as measured by protein misfolding cyclic amplification, used as a proxy for infectivity. Liquid chromatography-tandem mass spectrometry revealed that exposure to peroxymonosulfate results in oxidative modifications to methionine and tryptophan residues. This study indicates that peroxymonosulfate may hold promise for decontamination of prion-contaminated surfaces.

Potential role of soil properties in the spread of CWD in western Canada

Chronic wasting disease (CWD) is a horizontally transmissible prion disease of free ranging deer, elk and moose. Recent experimental transmission studies indicate caribou are also susceptible to the disease. CWD is present in southeast Alberta and southern Saskatchewan. This CWD-endemic region is expanding, threatening Manitoba and areas of northern Alberta and Saskatchewan, home to caribou. Soil can serve as a stable reservoir for infectious prion proteins; prions bound to soil particles remain infectious in the soils for many years. Soils of western Canada are very diverse and the ability of CWD prions to bind different soils and the impact of this interaction on infectivity is not known. In general, clay-rich soils may bind prions avidly and enhance their infectivity comparable to pure clay mineral montmorillonite. Organic components of soils are also diverse and not well characterized, yet can impact prion-soil interaction. Other important contributing factors include soil pH, composition of soil solution and amount of metals (metal oxides). In this review, properties of soils of the CWD-endemic region in western Canada with its surrounding terrestrial environment are described and used to predict bioavailability and, thus, potential spread of CWD. The major soils in the CWD-endemic region of Alberta and Saskatchewan are Chernozems, present in 60% of the total area; they are generally similar in texture, clay mineralogy and soil organic matter content, and can be characterized as clay loamy, montmorillonite (smectite) soils with 6-10% organic carbon. The greatest risk of CWD spread in western Canada relates to clay loamy, montmorillonite soils with humus horizon. Such soils are predominant in the southern region of Alberta, Saskatchewan and Manitoba, but are less common in northern regions of the provinces where quartz-illite sandy soils with low amount of humus prevail.

Effect of seepage velocity on the attachment efficiency of TiO2 nanoparticles in porous media

Previously identified relationships between the attachment efficiency (α) and seepage velocity (US) of nanoparticles (NPs) were tested under simulated subsurface transport conditions, where the value of US is typically much less than the US on which they are based. This found an increase in the α value of TiO2 NPs with respect to US, which contradicts previous reports suggesting a constant value or decrease. By comparing the adhesion energy of the TiO2 NPs to sand and the hydrodynamic energy required to detach them, the increase of α with respect to US is found to be due to the difference in the magnitude of US considered; with 6.1E-05 to 1.3E-03ms(-1) used in previous studies, whereas the current study uses a value in the range from 2.4E-06 to 4.9E-04ms(-1). Only one of the previous models predicting α showed a similar increase of α with US, which was the result of it employing low velocities to examine the effects of organic matter. The current findings therefore suggest that previously determined relationships between α and US need to be further developed to incorporate more variables before they can be effectively used to describe or predict the subsurface transport of TiO2 NPs.

Attachment of pathogenic prion protein to model oxide surfaces

Prions are the infectious agents in the class of fatal neurodegenerative diseases known as transmissible spongiform encephalopathies, which affect humans, deer, sheep, and cattle. Prion diseases of deer and sheep can be transmitted via environmental routes, and soil is has been implicated in the transmission of these diseases. Interaction with soil particles is expected to govern the transport, bioavailability and persistence of prions in soil environments. A mechanistic understanding of prion interaction with soil components is critical for understanding the behavior of these proteins in the environment. Here, we report results of a study to investigate the interactions of prions with model oxide surfaces (Al2O3, SiO2) using quartz crystal microbalance with dissipation monitoring and optical waveguide light mode spectroscopy. The efficiency of prion attachment to Al2O3 and SiO2 depended strongly on pH and ionic strength in a manner consistent with electrostatic forces dominating interaction with these oxides. The presence of the N-terminal portion of the protein appeared to promote attachment to Al2O3 under globally electrostatically repulsive conditions. We evaluated the utility of recombinant prion protein as a surrogate for prions in attachment experiments and found that its behavior differed markedly from that of the infectious agent. Our findings suggest that prions would tend to associate with positively charged mineral surfaces in soils (e.g., iron and aluminum oxides).

TiO2 nanoparticle exposure and illumination during zebrafish development: mortality at parts per billion concentrations

Photoactivation of titanium dioxide nanoparticles (TiO2NPs) can produce reactive oxygen species (ROS). Over time, this has the potential to produce cumulative cellular damage. To test this, we exposed zebrafish (Danio rerio) to two commercial TiO2NP preparations at concentrations ranging from 0.01 to 10,000 ng/mL over a 23 day period spanning embryogenesis, larval development, and juvenile metamorphosis. Fish were illuminated with a lamp that mimics solar irradiation. TiO2NP exposure produced significant mortality at 1 ng/mL. Toxicity included stunted growth, delayed metamorphosis, malformations, organ pathology, and DNA damage. TiO2NPs were found in the gills and gut and elsewhere. The two preparations differed in nominal particle diameter (12.1 ± 3.7 and 23.3 ± 9.8 nm) but produced aggregates in the 1 μm range. Both were taken up in a dose-dependent manner. Illuminated particles produced a time- and dose-dependent increase in 8-hydroxy-2'-deoxyguanosine DNA adducts consistent with cumulative ROS damage. Zebrafish take up TiO2NPs from the aqueous environment even at low ng/mL concentrations, and these particles when illuminated in the violet-near UV range produce cumulative toxicity.

Influence of humic acid on titanium dioxide nanoparticle toxicity to developing zebrafish

Titanium dioxide nanoparticle (TiO2NP) suspension stability can be altered by adsorption of dissolved organic matter (DOM). This is expected to impact their environmental fate and bioavailability. To date, the influence of DOM on the toxicity of TiO2NPs to aquatic vertebrates has not been reported. We examined the impact of Suwannee River humic acid (HA) on the toxicity of TiO2NPs to developing zebrafish (Danio rerio) in the dark and under simulated sunlight illumination. Adsorption of HA increased suspension stability and decreased TiO2NP exposure. TiO2NPs were more toxic in the presence of HA. In the absence of simulated sunlight, a small but significant increase in lethality was observed in fish exposed to TiO2NPs in the presence of HA. Under simulated sunlight illumination, photocatalytic degradation of HA reduced suspension stability. Despite the lower concentrations of Ti associated with fish in the treatments containing HA, under simulated sunlight illumination, median lethal concentrations were lower and oxidative DNA damage was elevated relative to fish exposed to TiO2NPs in the absence of HA. This study demonstrates the importance of considering environmental factors (i.e., exposure to sunlight, adsorption of DOM) when assessing the potential risks posed by engineered nanomaterials in the environment.

A Review of the Use of Organic Amendments and the Risk to Human Health

Historically, organic amendments—organic wastes—have been the main source of plant nutrients, especially N. Their use allows better management of often-finite resources to counter changes in soils that result from essential practices for crop production. Organic amendments provide macro- and micronutrients, including carbon for the restoration of soil physical and chemical properties. Challenges from the use of organic amendments arise from the presence of heavy metals and the inability to control the transformations required to convert the organic forms of N and P into the minerals available to crops, and particularly to minimize the losses of these nutrients in forms that may present a threat to human health. Animal manure and sewage biosolids, the organic amendments in greatest abundance, contain components that can be hazardous to human health, other animals and plants. Pathogens pose an immediate threat. Antibiotics, other pharmaceuticals and naturally produced hormones may pose a threat if they increase the number of zoonotic disease organisms that are resistant to multiple antimicrobial drugs or interfere with reproductive processes. Some approaches aimed at limiting N losses (e.g. covered liquid or slurry storage, rapid incorporation into the soil, timing applications to minimize delay before plant uptake) also tend to favor survival of pathogens. Risks to human health, through the food chain and drinking water, from the pathogens, antibiotics and hormonal substances that may be present in organic amendments can be reduced by treatment before land application, such as in the case of sewage biosolids. Other sources, such as livestock and poultry manures, are largely managed by ensuring that they are applied at the rate, time and place most appropriate to the crops and soils. A more holistic approach to management is required as intensification of agriculture increases.

Biodegradation of specified risk material and fate of scrapie prions in compost

Composting may be a viable alternative to rendering and land filling for the disposal of specified risk material (SRM) provided that infectious prion proteins (PrP(TSE)) are inactivated. This study investigated the degradation of SRM and the fate of scrapie prions (PrP(Sc)) over 28 days in laboratory-scale composters, with and without feathers in the compost matrices. Compost was mixed at day 14 to generate a second heating cycle, with temperatures exceeding 65°C in the first cycle and 50°C in the second cycle. Approximately 63% and 77% of SRM was degraded after the first and second cycles, respectively. Inclusion of feathers in the compost matrices did not alter compost properties during composting other than increasing (P < 0.05) total nitrogen and reducing (P < 0.05) the C/N ratio. However, addition of feathers enhanced (P < 0.05) SRM degradation by 10% upon completion of experiment. Scrapie brain homogenates were spiked into manure at the start of composting and extracted using sodium dodecyl sulphate followed by detection using Western blotting (WB). Prior to composting, PrP(Sc) was detectable in manure with 1-2 log(10) sensitivity, but was not observable after 14 or 28 days of composting. This may have been due to either biological degradation of PrP(Sc) or the formation of complexes with compost components that precluded its detection.

Effects of solution chemistry and aging time on prion protein adsorption and replication of soil-bound prions

Prion interactions with soil may play an important role in the transmission of chronic wasting disease (CWD) and scrapie. Prions are known to bind to a wide range of soil surfaces, but the effects of adsorption solution chemistry and long-term soil binding on prion fate and transmission risk are unknown. We investigated HY TME prion protein (PrP(Sc)) adsorption to soil minerals in aqueous solutions of phosphate buffered saline (PBS), sodium chloride, calcium chloride, and deionized water using western blotting. The replication efficiency of bound prions following adsorption in these solutions was also evaluated by protein misfolding cyclic amplification (PMCA). Aging studies investigated PrP(Sc) desorption and replication efficiency up to one year following adsorption in PBS or DI water. Results indicate that adsorption solution chemistry can affect subsequent prion replication or desorption ability, especially after incubation periods of 30 d or longer. Observed effects were minor over the short-term (7 d or less). Results of long-term aging experiments demonstrate that unbound prions or prions bound to a diverse range of soil surfaces can readily replicate after one year. Our results suggest that while prion-soil interactions can vary with solution chemistry, prions bound to soil could remain a risk for transmitting prion diseases after months in the environment.

Fate of prions in soil: a review

Prions are the etiological agents of transmissible spongiform encephalopathies (TSSEs), a class of fatal neurodegenerative diseases affecting humans and other mammals. The pathogenic prion protein is a misfolded form of the host-encoded prion protein and represents the predominant, if not sole, component of the infectious agent. Environmental routes of TSE transmission areimplicated in epizootics of sheep scrapie and chronic wasting disease (CWD) of deer, elk, and moose. Soil represents a plausible environmental reservoir of scrapie and CWD agents, which can persist in the environment for years. Attachment to soil particles likely influences the persistence and infectivity of prions in the environment. Effective methods to inactivate TSE agents in soil are currently lacking, and the effects of natural degradation mechanisms on TSE infectivity are largely unknown. An improved understanding of the processes affecting the mobility, persistence, and bioaviailability of prions in soil is needed for the management of TSE-contaminated environments.

Soil clay content underlies prion infection odds

Environmental factors—especially soil properties—have been suggested as potentially important in the transmission of infectious prion diseases. Because binding to montmorillonite (an aluminosilicate clay mineral) or clay-enriched soils had been shown to enhance experimental prion transmissibility, we hypothesized that prion transmission among mule deer might also be enhanced in ranges with relatively high soil clay content. In this study, we report apparent influences of soil clay content on the odds of prion infection in free-ranging deer. Analysis of data from prion-infected deer herds in northern Colorado, USA, revealed that a 1% increase in the clay-sized particle content in soils within the approximate home range of an individual deer increased its odds of infection by up to 8.9%. Our findings suggest that soil clay content and related environmental properties deserve greater attention in assessing risks of prion disease outbreaks and prospects for their control in both natural and production settings.

The infectious prion diseases affect numerous hoofed animal species, and it has been suggested that the properties of the local soil affect transmission of these diseases. Here, the authors studied two North American locations and demonstrate that soil clay content can influence the infection rate in deer.

Survival of infectious prions in Class B biosolids

This study developed a method for extracting infectious prions from Class B biosolids and subsequently evaluated the survival of infectious prions under the influence of mesophilic (37°C) and thermophilic (60°C) temperatures in Class B biosolids. Unlike other studies, this study utilized a scrapie cell assay to determine infectivity and quantity of infectious prions. The best method for extraction was exposing the biosolids to 4 M urea at 80°C for 10 minutes followed by a membrane centrifugation to reduce the concentration of urea. The recovery efficiency of the infectious prions from the biosolids for this method was 17.2%. In the survival study, a 2.43-log(10) reduction in prion infectivity was observed under mesophilic temperatures after 15 days and a 3.41-log(10) reduction after 10 days under thermophilic conditions. The reduction of infectious prions was greater in the biosolids than the control in phosphate buffered saline, suggesting factors other than temperature were also playing a role in the loss of infectivity of the prions in the biosolids.

Adsorption of transgenic insecticidal Cry1Ab protein to SiO2. 1. Forces driving adsorption

Genetically modified Bt crops express insecticidal Cry proteins (Bt toxins) that may enter agricultural soils. A mechanistic understanding of Cry protein adsorption to soils is critical for risk assessment, as this process governs Cry protein fate and bioavailability. We used quartz crystal microbalance and optical waveguide lightmode spectroscopy to elucidate the driving forces of the adsorption of monomeric Cry1Ab to negatively charged quartz (SiO(2)) and positively charged poly-L-lysine (PLL) at pH 5-8 and constant ionic strength of 50 mM (NaCl). Bovine serum albumin and hen egg white lysozyme were used as reference proteins because of their known adsorption behavior. Electrostatics governed Cry1Ab adsorption; as pH increased above the isoelectric point of Cry1Ab, the initial rate and the extent of adsorption decreased on SiO(2) and increased on PLL. Reversible adsorption to SiO(2) suggested weak Cry1Ab-SiO(2) electrostatic interactions and no irreversible conformational changes of Cry1Ab at the surface. High conformational stability of Cry1Ab was further supported by supply rate-independent extent of adsorption of Cry1Ab to apolar gold. Some evidence is presented that the nonuniform surface charge distribution of Cry1Ab resulted in patch-controlled electrostatic attraction with sorbents that carried the same net charge as Cry1Ab. A more detailed discussion of this mechanism is given in a companion paper.

Prions and manganese: A maddening beast

The prion protein is well known because of its association with prion diseases. These diseases, which include variant CJD, are unusual because they are neurodegenerative diseases that can be transferred between individuals experimentally. The prion protein is also widely known as a copper binding protein. The binding of copper to the prion protein is possibly necessary for its normal cellular function. The prion protein has also been suggested to bind other metals, and among these, manganese. Despite over ten years of research on manganese and prion disease, this interaction has often been dismissed or at best seen as a poor cousin to the involvement of copper. However, recent data has shown that manganese could stabilise prions in the environment and that chelation therapy specifically aimed at manganese can extend the life of animals with prion disease. This article reviews the evidence for a link between prions and manganese.

Anaerobic digestion of specified risk materials with cattle manure for biogas production

Biogas production from anaerobic digestion (AD) of specified risk materials (SRM) co-digested with cattle manure was assessed in a 3 x 2 factorial design. SRM replaced manure at 0 (control), 10% or 25% (w/w) as the substrate fed to six 2-L biodigesters maintained at 37 degrees C or 55 degrees C. Digesters were fed substrate (30 g L(-1) total volatile solids) at 6-d intervals for 90 d, with a retention time of 30 d. Keratin (<20mg) was added to each digester to model the degradation of beta-sheet rich proteins. Methane production was measured daily, and effluent was collected at feeding to monitor SRM degradation using real-time PCR analysis of bovine-specific DNA fragments. Compared with control, methane production increased by 83% or 161% (P<0.05) with 10% or 25% SRM at 37 degrees C, and by 45% and 87%, respectively, at 55 degrees C (P<0.05). Bovine DNA degradation over 6d was higher (P<0.05) at 37 degrees C as compared to 55 degrees C. Dry matter degradation of keratin at 37 degrees C decreased with increasing SRM concentration (P<0.05), whereas at 55 degrees C no difference between treatments was observed (P>0.05). Inclusion of SRM increases the production of methane during the anaerobic digestion of manure and may offer a means of deriving economic value from the disposal of SRM.

Transport of the pathogenic prion protein through soils

Transmissible spongiform encephalopathies (TSEs) are progressive neurodegenerative diseases and include bovine spongiform encephalopathy of cattle, chronic wasting disease (CWD) of deer and elk, scrapie in sheep and goats, and Creutzfeldt-Jakob disease in humans. An abnormally folded form of the prion protein (designated PrP(TSE)) is typically associated with TSE infectivity and may constitute the major, if not sole, component of the infectious agent. Transmission of CWD and scrapie is mediated in part by an environmental reservoir of infectivity. Soil appears to be a plausible candidate for this reservoir. The transport of TSE agent through soil is expected to influence the accessibility of the pathogen to animals after deposition and must be understood to assess the risks associated with burial of infected carcasses. We report the results of saturated column experiments designed to evaluate PrP(TSE) transport through five soils with relatively high sand or silt contents and low organic carbon content. Protease-treated TSE-infected brain homogenate was used as a model for PrP(TSE) present in decomposing infected tissue. Synthetic rainwater was used as the eluent. All five soils retained PrP(TSE); no detectable PrP(TSE) was eluted over more than 40 pore volumes of flow. Lower bound apparent attachment coefficients were estimated for each soil. Our results suggest that TSE agent released from decomposing tissues to soils with low organic carbon content would remain near the site of initial deposition. In the case of infected carcasses deposited on the land surface, this may result in local sources of infectivity to other animals.

Prion protein adsorption to soil in a competitive matrix is slow and reduced

It is likely that the soil environment serves as a stable reservoir of infectious CWD and scrapie prions as well as a potential reservoir of BSE. Prion adsorption to soil could play an important role in prion mobility, proteolysis, and infectivity. We modified previously published methods to quantify adsorbed prions via direct detection and studied prion adsorption to soil and soil minerals as a function of time through 60 days. Prion-infected brain homogenate was used as a complex, relevant prion source. We determined that maximum PrP adsorption requires days or weeks, depending on the soil or mineral, and is 2-5 orders of magnitude lower than previous studies using purified PrP(Sc) or recPrP. Because PrP adsorption to soil is slow and reduced in tissue homogenate, the possibility of prion transport in soil environments cannot be excluded and requires further investigation. Our results indicate that binding to soil may protect prions from degradation, consistent with prions' longevity in the environment. Adsorption of PrP to sterilized soil did not differ significantly from adsorption to unsterilized soil, which suggests that active biological processes do not significantly affect prion adsorption or degradation in the soil environment.

Influence of prion strain on prion protein adsorption to soil in a competitive matrix

It is likely that the soil environment serves as a stable reservoir of infectious chronic wasting disease (CWD) and scrapie prions, as well as a potential reservoir of bovine spongiform encephalopathy (BSE, or "mad cow" disease). Prion adsorption to soil may play an important role in prion mobility, proteolysis, and infectivity. Differences in PrP environmental fate are possible due to the strain- and species-dependent structure of PrP(Sc). Kinetic and isothermal studies of PrP adsorption to sand and two whole soils were conducted using HY and DY TME-infected hamster, uninfected hamster, and CWD-infected elk brain homogenates as competitive PrP sources. The role of the N-terminus in PrP adsorption was also investigated. We report strain and species differences in PrP adsorption to soil over time and as a function of aqueous concentration, indicating that the fate of prions in the environment may vary with the prion strain and species infected. Our data also provide evidence that the N-terminal region of PrP enhances adsorption to clay but may hinder adsorption to sand. PrP adsorption was maximal at an intermediate aqueous concentration, most likely due to the competitive brain homogenate matrix in which it enters the soil environment.

Transport of the pathogenic prion protein through landfill materials

Transmissible spongiform encephalopathies (TSEs, prion diseases) are a class of fatal neurodegenerative diseases affecting a variety of mammalian species including humans. A misfolded form of the prion protein (PrP(TSE)) is the major, if not sole, component of the infectious agent RecentTSE outbreaks in domesticated and wild animal populations have created the need for safe and effective disposal of large quantities of potentially infected materials. Here, we report results of a study to evaluate the potential for transport of PrP(TSE) derived from carcasses and associated wastes in municipal solid waste (MSW) landfills. Column experiments were conducted to evaluate PrP(TSE) transport in quartz sand, two fine-textured burial soils currently used in landfill practice, a green waste residual material (a potential burial material), and fresh and aged MSW. PrP(TSE) was retained by quartz sand and the fine-textured burial soils, with no detectable PrP(TSE) eluted over more than 40 pore volumes. In contrast, PrP(TSE) was more mobile in MSW and green waste residual. Transport parameters were estimated from the experimental data and used to model PrP(TSE) migration in a MSW landfill. To the extent that the PrP(TSE) used mimics that released from decomposing carcasses and the column experiments adequately simulate prion transport through burial soils, burial of CWD-infected materials at MSW landfills could provide secure containment of PrP(TSE) provided reasonable burial strategies (e.g., encasement in fine-grained soil) are used.

Pathogenic prion protein is degraded by a manganese oxide mineral found in soils

Prions, the aetiological agents of transmissible spongiform encephalopathies, exhibit extreme resistance to degradation. Soil can retain prion infectivity in the environment for years. Reactive soil components may, however, contribute to the inactivation of prions in soil. Members of the birnessite family of manganese oxides (MnO(2)) rank among the strongest natural oxidants in soils. Here, we report the abiotic degradation of pathogenic prion protein (PrP(TSE)) by a synthetic analogue of naturally occurring birnessite minerals. Aqueous MnO(2) suspensions degraded the PrP(TSE) as evidenced by decreased immunoreactivity and diminished ability to seed protein misfolding cyclic amplification reactions. Birnessite-mediated PrP(TSE) degradation increased as a solution's pH decreased, consistent with the pH-dependence of the redox potential of MnO(2). Exposure to 5.6 mg MnO(2) ml(-1) (PrP(TSE) : MnO(2)=1 : 110) decreased PrP(TSE) levels by > or = 4 orders of magnitude. Manganese oxides may contribute to prion degradation in soil environments rich in these minerals.

Grey-iron foundry slags as reactive media for removing trichloroethylene from groundwater

A feasibility study was conducted using slags from six grey-iron foundries to evaluate their potential as reactive media for permeable reactive barriers (PRBs) to remove aqueous trichloroethylene (TCE) from groundwater. Batch tests indicated that the slags exhibit varying degrees of reactivity ranging from nonreactive to reactivity comparable to that obtained with commercially available granular zerovalent iron on a surface-area-normalized basis. TCE removal follows pseudo-first-order kinetics, and produces lesser-chlorinated ethene byproducts (e.g., 1,1-DCE, cis-DCE). Greater reactivity was obtained with the slags having the highest iron content and the lowest reactivity was obtained with the slag having the lowest iron content, suggesting that iron is a primary reductant in the slags. Batch tests on the two most reactive slags indicated that the rate coefficients are linearly related to surface area over the range tested, and are sensitive to initial TCE concentration. Column studies showed that reactivity is lower under flow-through conditions than anticipated based on batch tests. Calculations indicate a 2-m-thick slag PRB can degrade TCE to less than 0.005 mg/L for influent concentrations less than 2 mg/L at seepage velocities below 0.1 m/d.

Concentration of disease-associated prion protein with silicon dioxide

Reagents that can precipitate the disease-associated prion protein (PrP(Sc)) are vital for the development of high sensitivity tests to detect low levels of this disease marker in biological material. Here, a range of minerals are shown to precipitate both ovine cellular prion protein (PrP(C)) and ovine scrapie PrP(Sc). The precipitation of prion protein with silicon dioxide is unaffected by PrP(Sc) strain or host species and the method can be used to precipitate bovine BSE. This method can reliably concentrate protease-resistant ovine PrP(Sc) (PrP(res)) derived from 1.69 microg of brain protein from a clinically infected animal diluted into either 50 ml of buffer or 15 ml of plasma. The introduction of a SiO(2) precipitation step into the immunological detection of PrP(res) increased detection sensitivity by over 1,500-fold. Minerals such as SiO(2) are readily available, low cost reagents with generic application to the concentration of diseases-associated prion proteins.

Prions in the environment: occurrence, fate and mitigation

Scrapie and CWD are horizontally transmissible, and the environment likely serves as a stable reservoir of infectious prions, facilitating a sustained incidence of CWD in free-ranging cervid populations and complicating efforts to eliminate disease in captive herds. Prions will enter the environment through mortalities and/or shedding from live hosts. Unfortunately, a sensitive detection method to identify prion contamination in environmental samples has not yet been developed. An environmentally-relevant prion model must be used in experimental studies. Changes in PrP(Sc) structure upon environmental exposure may be as significant as changes in PrP(Sc) quantity, since the structure can directly affect infectivity and disease pathology. Prions strongly bind to soil and remain infectious. Conformational changes upon adsorption, competitive sorption and potential for desorption and transport all warrant further investigation. Mitigation of contaminated carcasses or soil might be accomplished with enzyme treatments or composting in lieu of incineration.

Environmentally-relevant forms of the prion protein

Scrapie and chronic wasting disease (CWD) are prion diseases of particular environmental concern as they are horizontally transmissible and can remain infectious after years in the environment. Recent evidence suggests that the N-terminus of PrPSC, the infectious conformation of the prion protein, plays an important role in the mechanism of sorption to soil particles. We hypothesize that, in a prion-infected animal carcass, a portion of the N-terminus of PrPSc could be cleaved by proteinases in the brain at ordinary temperatures. Hamster (HY transmissible mink encephalopathy-infected), transgenic mice (CWD-infected), and elk (CWD-infected) brain homogenates were incubated at 22 and 37 degrees C for up to 1 month and then analyzed by Western blot using N-terminal and middle region monoclonal anti-PrP antibodies. For all three systems, there was a very faint or undetectable N-terminal PrP signal after 35 days at both temperatures, which indicates that full-length PrPSc might be rare in the brain matter of animal carcasses. Future studies on prion-soil interactions should therefore consider N-terminal-degraded PrPSc in addition to the full-length form. Both mouse and elk CWD PrPSc demonstrated greater resistance to degradation than HY TME PrPSc. This indicates that the transgenic mouse-CWD model is a good surrogate for natural CWD prions, but that other rodent prion models might not accurately represent CWD prion fate in the environment.

Prion stability and infectivity in the environment

The biology of normal prion protein and the property of infectivity observed in abnormal folding conformations remain thinly characterized. However, enough is known to understand that prion proteins stretch traditional views of proteins in biological systems. Numerous investigators are resolving details of the novel mechanism of infectivity, which appears to feature a protein-only, homologous replication of misfolded isoforms. Many other features of prion biology are equally extraordinary. This review focuses on the status of infectious prions in various natural and man-made environments. The picture that emerges is that prion proteins are durable under extreme conditions of environmental exposure that are uncommon in biological phenomena, and this durability offers the potential for environmental reservoirs of persistent infectivity lasting for years. A recurrent theme in prion research is a propensity for these proteins to bind to mineral and metal surfaces, and several investigators have provided evidence that the normal cellular functions of prion protein may include metalloprotein interactions. This structural propensity for binding to mineral and metal ions offers the hypothesis that prion polypeptides are intrinsically predisposed to non-physiological folding conformations that would account for their environmental durability and persistent infectivity. Similarly, the avidity of binding and potency of prion infectivity from environmental sources also offers a recent hypothesis that prion polypeptides bound to soil minerals are actually more infectious than studies with purified polypeptides would predict. Since certain of the prion diseases have a history of epidemics in economically important animal species and have the potential to transmit to humans, urgency is attached to understanding the environmental transmission of prion diseases and the development of protocols for their containment and inactivation.

Oral transmissibility of prion disease is enhanced by binding to soil particles

Soil may serve as an environmental reservoir for prion infectivity and contribute to the horizontal transmission of prion diseases (transmissible spongiform encephalopathies [TSEs]) of sheep, deer, and elk. TSE infectivity can persist in soil for years, and we previously demonstrated that the disease-associated form of the prion protein binds to soil particles and prions adsorbed to the common soil mineral montmorillonite (Mte) retain infectivity following intracerebral inoculation. Here, we assess the oral infectivity of Mte- and soil-bound prions. We establish that prions bound to Mte are orally bioavailable, and that, unexpectedly, binding to Mte significantly enhances disease penetrance and reduces the incubation period relative to unbound agent. Cox proportional hazards modeling revealed that across the doses of TSE agent tested, Mte increased the effective infectious titer by a factor of 680 relative to unbound agent. Oral exposure to Mte-associated prions led to TSE development in experimental animals even at doses too low to produce clinical symptoms in the absence of the mineral. We tested the oral infectivity of prions bound to three whole soils differing in texture, mineralogy, and organic carbon content and found soil-bound prions to be orally infectious. Two of the three soils increased oral transmission of disease, and the infectivity of agent bound to the third organic carbon-rich soil was equivalent to that of unbound agent. Enhanced transmissibility of soil-bound prions may explain the environmental spread of some TSEs despite the presumably low levels shed into the environment. Association of prions with inorganic microparticles represents a novel means by which their oral transmission is enhanced relative to unbound agent.

Transmissible spongiform encephalopathies (TSEs) are a group of incurable neurological diseases likely caused by a misfolded form of the prion protein. TSEs include scrapie in sheep, bovine spongiform encephalopathy (“mad cow” disease) in cattle, chronic wasting disease in deer and elk, and Creutzfeldt-Jakob disease in humans. Scrapie and chronic wasting disease are unique among TSEs because they can be transmitted between animals, and the disease agents appear to persist in environments previously inhabited by infected animals. Soil has been hypothesized to act as a reservoir of infectivity and to bind the infectious agent. In the current study, we orally dosed experimental animals with a common clay mineral, montmorillonite, or whole soils laden with infectious prions, and compared the transmissibility to unbound agent. We found that prions bound to montmorillonite and whole soils remained orally infectious, and, in most cases, increased the oral transmission of disease compared to the unbound agent. The results presented in this study suggest that soil may contribute to environmental spread of TSEs by increasing the transmissibility of small amounts of infectious agent in the environment.

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.

Sensitive detection of PrPSc by Western blot assay based on streptomycin sulphate precipitation

Transmissible spongiform encephalopathies, also termed prion diseases, are fatal neurodegenerative disorders that affect both humans and animals, which are characterized by presences of protease-resistance disease-associated prion protein (PrP(Sc)) in brains. In the present study, we optimized the Western blot assay for PrP(Sc) with a precipitation procedure of streptomycin sulphate. After incubated with suitable amount of streptomycin sulphate, the detective sensitivity for PrP(Sc) was remarkably improved. The precipitation of PrP(Sc) was obviously influenced by pH value in the solution. Employs of PrP(Sc) stock sample into various mimic specimens, including normal hamster brain homogenate, human cerebrospinal fluid and urine, demonstrated that streptomycin precipitation markedly increased the detective sensitivity of PrP(Sc), regardless in low concentration or in large volume. In addition, the PrP(Sc) from a human brain tissue of familiar Creutzfeldt-Jakob disease (fCJD) was efficiently precipitated with streptomycin sulphate. As a sensitive, specific, rapid and flexible protocol for PrP(Sc), the protocol in this study has the potential, alone or combined with other techniques, to detect low levels of PrP(Sc) in the specimens not only from central nerve system, but also from peripheral organs or fluids.

Direct detection of soil-bound prions

Scrapie and chronic wasting disease are contagious prion diseases affecting sheep and cervids, respectively. Studies have indicated that horizontal transmission is important in sustaining these epidemics, and that environmental contamination plays an important role in this. In the perspective of detecting prions in soil samples from the field by more direct methods than animal-based bioassays, we have developed a novel immuno-based approach that visualises in situ the major component (PrP^Sc) of prions sorbed onto agricultural soil particles. Importantly, the protocol needs no extraction of the protein from soil. Using a cell-based assay of infectivity, we also report that samples of agricultural soil, or quartz sand, acquire prion infectivity after exposure to whole brain homogenates from prion-infected mice. Our data provide further support to the notion that prion-exposed soils retain infectivity, as recently determined in Syrian hamsters intracerebrally or orally challanged with contaminated soils. The cell approach of the potential infectivity of contaminated soil is faster and cheaper than classical animal-based bioassays. Although it suffers from limitations, e.g. it can currently test only a few mouse prion strains, the cell model can nevertheless be applied in its present form to understand how soil composition influences infectivity, and to test prion-inactivating procedures.