Diversity and Abundance of Ammonia-oxidizing Archaea in the Dongjiang River, China

Nitrification in aquatic ecosystems plays a crucial role in the global nitrogen cycling. It has been widely accepted that ammonia-oxidizing bacteria (AOB) are responsible for nitrification. However, this concept is currently challenged by the ubiquity of ammonia-oxidizing archaea (AOA) in various environments, such as in aquatic and terrestrial ecosystems. In this study, the presence of AOA in the Dongjiang River was documented via archaeal amoA amplification; the abundance of archaeal and bacterial amoA genes were estimated by quantitative polymerase chain reaction (qPCR), and the diversity was investigated by sequencing of archaeal amoA gene. Based on retrieved sequences and phylogenetic analysis, the majority of sequences obtained were different from Crenarchaeota phylum of marine and soil, affiliated with Freshwater Cluster 1 crenarchaeota. The results showed that the AOA detected fell into clusters which are specifically associated with freshwater habitats, and AOA was more abundance than AOB by around 2-4 orders of magnitude. Furthermore, it was found that AOA was more prefer to aerobic and relative low-ammonia concentrations in fresh water. Our finding provides a vital supplement to the distribution of AOA in global pattern, and offers implications for further understanding of the potential role of ammonia oxidizers in river ecosystems.