Microbial ecology of nitrous oxide-reducing denitrifying bacteria in the livestock waste composts

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In this study we performed composting experiments using solidwastes from piggery wastewater treatment processes. Our results indicated that the timing of N_2O emission follows emergence of ammonia-oxidizing bacteria, which produce denitrification substrates such as nitrate and nitrite. We also found that hyperthermophilic pre-treatment reduces N_2O emission from composting, which is suggest to have been caused by denitrifying bacteria with N_2O-reducing activities. Phylogenetic analyses showed that community structures of ammonia-oxidizing bacteria and denitrifying bacteria dynamically changed as composting proceeded. Denitrifying bacterial strains isolated from our compost samples were able to perform denitrification under oxic or microoxic conditions. These findings collectively suggest that N_2O emission patterns during composting is strongly affected by community structures and functions of ammonia-oxidizing bacteria and denitrifying bacteria, which should be effectively controlled to reduce N_2O emission from composting processes.