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

Shun Chen,Kaiwen Ta,Hengchao Xu,Xiaotong Peng

doi:10.5194/bg-13-2051-2016

Abstract

Abstract. 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 amoA 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 amoA was not detected. Phylogenetic analysis of 16S rRNA genes showed high sequence similarity to thermophilic Candidatus 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.

Highlights

Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many ecosystems (Vitousek et al, 1997)
In combination of cultureindependent (fluorescence in situ hybridization, quantitative polymerase chain reaction (PCR), and clone library) and culture-dependent (15N pool dilution technique) approaches, we provide direct evidence that ammonia-oxidizing Archaea (AOA) are responsible for the major portion of ammonia oxidation in hightemperature hot spring environments
Combination of 15N-NO−3 pool dilution and molecular analyses demonstrate that the oxidation of ammonia by AOA occurs actively in the high-temperature the Gongxiaoshe geothermal system

Summary

Introduction

Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many ecosystems (Vitousek et al, 1997). Some studies have elucidated nitrogen metabolism and cycling in high-temperature hot spring ecosystems (Dodsworth et al, 2011b; Nishizawa et al, 2013; Gerbl et al, 2014). In such systems, there has been evidence of microbial communities oxidizing ammonia, the first and rate-limiting step of nitrification (Reigstad et al, 2008; Hatzenpichler et al, 2008). L. Zhang et al, 2008)

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Discussion

Conclusion