Biodegradation of bovine spongiform encephalopathy prions in compost.

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