Biodegradation of specified risk material and characterization of actinobacterial communities in laboratory-scale composters

Abstract

As a result of bovine spongiform encephalopathy in Canada, specific tissues at risk of harbouring prions are not allowed to enter the food chain. Composting may be a viable alternative to rendering and land filling for the disposal of specified risk material (SRM). Two types of laboratory-scale composters, actively-heated and ambient systems were constructed to assess the biodegradation of SRM over 30 days. A second heating cycle was generated by mixing the compost after 15 days. Compared to ambient composters, temperature profiles in actively-heated composters were above 50°C for 5 and 4 days longer in the first and second composting cycles, respectively. Degradation of SRM was similar between two composter types during two composting cycles, averaging 52.2% in the first cycle and 43.9% in second cycle. Denaturing gradient gel electrophoresis (DGGE) revealed that changes in the actinobacteria populations in the first composting cycle were of a temporal nature, whereas alterations in populations in the second composting cycle were more related to active heating of compost. Sequencing of the dominant DGGE bands showed the predominance of Corynebacterium, Promicromonospora, Pseudonocardia, and Thermobifida in the first composting cycle and Corynebacterium, Mycobacterium, Nocardia, Saccharomonospora, and Streptomyces in the second composting cycle. Active heating can alter the nature of actinobacteria populations in compost, but does not appear to have a major impact on the extent of degradation of SRM.

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

“…3) a value comparable to, or even higher than that observed in previous experiments in our laboratory. [21,33] Xu et al [10] also found that SRM was rapidly degraded (>90%) after the first 7 days in a biosecure composting system. This period of rapid SRM degradation corresponded with an increase in microbial biomass as indicated by phospholipid fatty acid profiles within this passively aerated laboratory composter.…”

“…2), probably due to a large amount of free nitrogen being released into the surrounding compost from the degradation of SRM. [32][33] As feathers contain 16% nitrogen, their substitution for manure lowered (P < 0.05) the C/N ratio (Table 1), which may have negatively impacted the Values are cited from Xu et al [21] . nm, not measured.…”

“…Over 28 days, there was considerable evidence of microbial activity in compost as indicated by peak temperature >70 • C, 5 days of thermophilic composting, significant reduction in TC content, and degradation of ∼ 80% of the SRM. In addition, some bacteria with the ability to degrade recalcitrant proteins such as keratin and PrP TSE , including those of the genera Actinomadura, [11] Streptomyces, [13] , and Saccharomonospora, [49] have been shown to be present in compost [33] and may play a role in the degradation of PrP Sc . …”

Biodegradation of bovine spongiform encephalopathy prions in compost

“…Long term exposure to proteases under these conditions raises the possibility that the microbial consortia in compost may have the capacity to degrade PrP BSE . Achieving thermophilic temperatures for a prolonged duration may be a key indictor of the potential to biodegrade SRM and inactivate PrP BSE in compost 16 , 17 .…”