Nitrification of archaeal ammonia oxidizers in a high- temperature hot spring

• Main Authors: S. Chen, X. Peng, H. Xu, K. Ta
• Format: Article
• Language: English
• Published: Copernicus Publications 2016-04-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/13/2051/2016/bg-13-2051-2016.pdf

The oxidation of ammonia by microbes has been shown to occur in diverse natural environments. However, the link of in situ nitrification activity to taxonomic identities of ammonia oxidizers in high-temperature environments remains poorly understood. Here, we studied in situ ammonia oxidation rates and the diversity of ammonia-oxidizing Archaea (AOA) in surface and bottom sediments at 77 °C in the Gongxiaoshe hot spring, Tengchong, Yunnan, China. The in situ ammonia oxidation rates measured by the ¹⁵N-NO₃⁻ pool dilution technique in the surface and bottom sediments were 4.80 and 5.30 nmol N g⁻¹ h⁻¹, respectively. Real-time quantitative polymerase chain reaction (qPCR) indicated that the archaeal 16S rRNA genes and <i>amoA</i> genes were present in the range of 0.128 to 1.96  ×  10⁸ and 2.75 to 9.80  ×  10⁵ gene copies g⁻¹ sediment, respectively, while bacterial <i>amoA</i> was not detected. Phylogenetic analysis of 16S rRNA genes showed high sequence similarity to thermophilic <i>Candidatus</i> Nitrosocaldus yellowstonii, which represented the most abundant operational taxonomic units (OTU) in both surface and bottom sediments. The archaeal predominance was further supported by fluorescence in situ hybridization (FISH) visualization. The cell-specific rate of ammonia oxidation was estimated to range from 0.410 to 0.790 fmol N archaeal cell⁻¹ h⁻¹, higher than those in the two US Great Basin hot springs. These results suggest the importance of archaeal rather than bacterial ammonia oxidation in driving the nitrogen cycle in terrestrial geothermal environments.