Composting as a method for disposal of specified risk material and degradation of prions

  • Author / Creator
    Xu, Shanwei
  • Provided that infectious prions (PrPTSE) are inactivated, composting of specified risk material (SRM) may be a viable alternative to rendering and land filling. The overall objective of this research was to utilize laboratory-scale composters to assess the degradation of SRM and PrPTSE during composting. Under non-containment conditions, co-composting of SRM with cattle manure revealed that SRM was degraded rapidly in compost, with approximately 60% and 80% dry matter loss after 14 and 28 days, respectively. Composter depth, types of bulking agent, or prolongation of thermophilic temperature using a water jacket did not influence SRM degradation. However, mixing of feathers with manure increased the extent of SRM degradation. Phospholipid fatty acid (PLFA) profiles demonstrated that both mesophilic and thermophilic microbial communities were responsible for SRM degradation. Furthermore, PCR-denaturing gradient gel electrophoresis (DGGE) analysis suggested that bacterial genera of Thermoactinomycetaceae, Thiohalospira, Pseudomonas, Enterobacter, Corynebacterium, Promicromonospora, Pseudonocardia, Thermobifida, Mycobacterium, Nocardia, Saccharomonospora, Streptomyces, Actinomadura, and fungal genera of Dothideomycetes, Cladosporium, Chaetomium, and Trichaptum may play a role in SRM degradation in compost. Prior to and after 14 or 28 days of composting, PrPTSE was detected by Western blotting (WB) after extraction using sodium dodecyl sulphate (SDS) and sodium phosphotungstic acid (PTA) precipitation. The WB findings suggested at least 1-2 log10 reduction of PrPTSE signals after 14 to 28 days of composting. Although scrapie prions (PrPSc) degradation can not be definitively concluded, the disappearance of chronic wasting disease prions (PrPCWD) and bovine spongiform encephalopathy prions (PrPBSE) may reflect biological degradation in compost. This is the first study to investigate possible biological degradation of PrPCWD and PrPBSE during composting, suggesting that it has merit as a means of SRM disposal.

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    Doctor of Philosophy
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