Diversity of ammonia-oxidizing bacteria and ammonia-oxidizing archaea during composting of municipal sludge

Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) play an important role in the oxidation of ammonia. The diversity and relative abundance of AOA and AOB in compost samples from four composting stages [initial (day 0), heating (day 3), thermophilic (day 12), and cooling (day 28) stage ] were analyzed using the amoA gene as a functional marker. The number of operational taxonomic units (OTUs) found in each stage during sewage sludge composting was 33.3 % to 66.6 % of the total OTUs for AOB and 43.8 % to 62.5 % for AOA, with OTUs defined on the basis of a 5 % difference in nucleotides. Phylogenetic analysis showed that the AOB amoA sequences related to the Nitrosomonas lineage were dominant throughout the entire composting process. Most of the AOA amoA sequences fell into a soil/sediment cluster containing “Candidatus Nitrososphaera gargensis”. These results indicate that different ammonia oxidizers were present in different stages during composting, but that the dominant phylogenetic types were stable.