Diversity and abundance of ammonia-oxidizing bacteria and ammonia-oxidizing archaea during cattle manure composting.

Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) play important roles in nitrification in various environments. They may also be key communities for ammonia oxidation in composting systems, although few studies have discussed their presence. We investigated the relative diversity and abundance of AOB and AOA using cloning procedures, denaturing gradient gel electrophoresis analysis, and real-time PCR during several stages in the process of cattle manure composting. Our results revealed that the AOB community structure changed during the process. At the high-temperature stage (>60°C), a member of the Nitrosomonas europaea/eutropha cluster dominated while the uncultured Nitrosomonas spp. cluster appeared after the temperature decreased. Additionally, our analysis indicated that AOA sequences, which were classified into a soil/sediment cluster, were present after the temperature decreased during the composting process. At these stages, the number of the archaeal amoA gene copies (3.2 or 3.9 × 10(7) copies per gram freeze-dried compost) was significantly higher than that of bacterial amoA gene copies (2.2-7.2 × 10(6) copies per gram freeze-dried compost). Our results suggest that both AOB and AOA are actively involved in nitrification of composting systems.