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Aim: A comprehensive understanding of the microbial community is necessary to ensure a significant reduction in pathogens during the composting process. Methods and Results: Two biosecure, static composting systems containing cattle mortalities were constructed at subzero temperatures. Temperature at each sampling site was measured continuously and samples were grouped as either ≤50 or ≥55°C, based on temperature exposure required for effective pathogen inactivation during composting. High-throughput 454 sequencing was used to characterize the bacterial communities within each sample. Clustering of bacterial communities was observed according to temperature. However, neither richness nor diversity differed between temperature groups. Firmicutes was the most abundant phylum within both temperature groups but was more pronounced (63Á6%) in samples ≥55°C (P < 0Á05). Similarly, members of Clostridia, Clostridium sensu stricto (3Á64%), Clostridium XI (0Á59%), UF (Clostridiaceae 1) (5Á29%) and UF (Clostridiales Incertae Sedis XI) (6Á20%), were prominent at ≥55°C (P < 0Á05), likely a reflection of spore survival and/or anaerobic microenvironments within passively aerated compost piles. Members of Thermobifida (3Á54%), UO (Actinomycetales) (12Á29%) and UO (Bacillales) (19Á49%) were also prominent at ≥55°C (P < 0Á05). Conclusion: Substantial spatial diversity exists within bacterial communities in field-scale compost piles. Localized temperature at the site of sampling may be one of the factors contributing to this phenomenon. Significance and Impact of the Study: This is the first study to describe the microbial community profile with the use of targeted 16S rRNA highthroughput sequencing in passively aerated composted livestock mortalities.

f Mycobacterium avium subsp. paratuberculosis causes Johne's disease (JD) in ruminants, with substantial economic impacts on the cattle industry. Johne's disease is known for its long latency period, and difficulties in diagnosis are due to insensitivities of current detection methods. Eradication is challenging as M. avium subsp. paratuberculosis can survive for extended periods within the environment, resulting in new infections in naïve animals (W. Xu et al., J. Environ. Qual. 38:437-450, 2009). This study explored the use of a biosecure, static composting structure to inactivate M. avium subsp. paratuberculosis. Mycobacterium smegmatis was also assessed as a surrogate for M. avium subsp. paratuberculosis. Two structures were constructed to hold three cattle carcasses each. Naturally infected tissues and ground beef inoculated with laboratory-cultured M. avium subsp. paratuberculosis and M. smegmatis were placed in nylon and plastic bags to determine effects of temperature and compost environment on viability over 250 days. After removal, samples were cultured and growth of both organisms was assessed after 12 weeks. After 250 days, M. avium subsp. paratuberculosis was still detectable by PCR, while M. smegmatis was not detected after 67 days of composting. Furthermore, M. avium subsp. paratuberculosis remained viable in both implanted nylon and plastic bags over the composting period. As the compost never reached a homogenous thermophilic (55 to 65°C) state throughout each structure, an in vitro experiment was conducted to examine viability of M. avium subsp. paratuberculosis after exposure to 80°C for 90 days. Naturally infected lymph tissues were mixed with and without compost. After 90 days, M. avium subsp. paratuberculosis remained viable despite exposure to temperatures typically higher than that achieved in compost. In conclusion, it is unlikely composting can be used as a means of inactivating M. avium subsp. paratuberculosis associated with cattle mortalities.