Common Soil Mineral Degrades the Nearly Indestructible Prion

Researchers have found that a common soil mineral can penetrate the prion and degrade the protein.

Prions living in the soil can ravage entire deer herds.

In the rogues' gallery of microscopic infectious agents, the prion is the toughest hombre in town. Warped pathogens that lack both DNA and RNA, prions are believed to cause such fatal brain ailments as chronic wasting disease (CWD) in deer and moose, mad cow disease in cattle, scrapie in sheep and Creutzfeldt-Jakob disease in humans.

In addition to being perhaps the weirdest infectious agent known to science, the prion is also the most durable. It resists almost every method of destruction from fire and ionizing radiation to chemical disinfectants and autoclaving, which reduce prion infectivity but fail to completely eliminate it.

Now, a team of Wisconsin researchers has found that a common soil mineral—an oxidized from of manganese known as birnessite—can penetrate the prion's armor and degrade the protein. The finding may yield ways to decontaminate soil and other environments where prions reside.

"Prions are resistant to many of the conventional means of inactivating pathogens," says Joel Pedersen, a UW-Madison environmental chemist and member of the study team. Autoclaving, a standard method for sterilization in the laboratory, for example, will reduce the concentration of prions in a sample, but won’t eliminate them altogether, as it does for virtually all other types of pathogens.

Because prions infect both wild and domesticated animals, the agent can contaminate barnyards and other areas where infected livestock are kept, as well as persist in natural environments where deer, elk and other animals can become infected by contact with contaminated soil.

Other studies have shown that prions can survive in the soil for at least three years, and that soil is a plausible route of transmission for some animals, Pedersen says. "We know that environmental contamination occurs in deer and sheep at least," he said.

Manganese oxides like birnessite are commonly used in such things as batteries and are among the most potent oxidants occurring naturally in soils, capable of chemically transforming a substance by adding oxygen atoms and stripping away electrons. The mineral is most abundant in soils that are seasonally waterlogged or poorly drained.

The study was conducted on prions in solution in the laboratory. The next step is to mix the mineral with contaminated soil to see if it has the same effect. If it does, birnessite may become a useful tool for cleaning up contaminated farmyards and other places where the prion may be concentrated in the soil.

The study was reported this month in the Journal of General Virology.

In addition to Pedersen, co-authors include Fabio Russo at the University of Naples, Christopher Johnson and Chad J. Johnson of the UW-Madison, and Judd Aiken and Debbie McKenzie of the University of Alberta.

The work was supported by grants from the National Science Foundation, the U.S. Environmental Protection Agency and the U.S. Department of Defense.

—By Terry Devitt/UW-Madison.

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