High Abundance of Thaumarchaeota Found in Deep Metamorphic Subsurface in Eastern China.

Wenhui Zhang,Xiangzhi Zeng,Hailiang Dong,Shang Wang,Weiguo Hou

doi:10.3390/microorganisms10030542

Abstract

Members of the Thaumarchaeota phylum play a key role in nitrogen cycling and are prevalent in a variety of environments including soil, sediment, and seawater. However, few studies have shown the presence of Thaumarchaeota in the terrestrial deep subsurface. Using high-throughput 16S rRNA gene sequencing, this study presents evidence for the high relative abundance of Thaumarchaeota in a biofilm sample collected from the well of Chinese Continental Scientific Drilling at a depth of 2000 m. Phylogenetic analysis showed a close relationship of these thaumarchaeotal sequences with known ammonia-oxidizing archaea (AOA) isolates, suggesting the presence of AOA in the deep metamorphic environment of eastern China which is believed to be oxic. Based on fluid geochemistry and FAProTax functional prediction, a pathway of nitrogen cycling is proposed. Firstly, heterotrophic nitrogen fixation is executed by diazotrophic bacteria coupled with methane oxidation. Then, ammonia is oxidized to nitrite by AOA, and nitrite is further oxidized to nitrate by bacteria within the phylum Nitrospirae. Denitrification and anaerobic ammonia oxidation occur slowly, leading to nitrate accumulation in the subsurface. With respect to biogeochemistry, the reaction between downward diffusing O2 and upward diffusing CH4 potentially fuels the ecosystem with a high relative abundance of Thaumarchaeota.

Highlights

Formation of the biofilm suggested a high abundance of biomass in the metamorphic rock of the deep subsurface in eastern China, which was consistent with previous studies of samples from the same borehole [28,39,40]
In Chinese Continental Scientific Drilling Project (CCSD) rocks, the biomass was generally higher than 104 cell/g rock after staining of high porosity rocks with 40,6-diamidino-2-phenylindole (DAPI) [40]
Thaumarchaeota are an important group of microorganisms onportion

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Thaumarchaeota—the third designated archaeal phylum, previously considered to be a lineage of the phylum Crenarchaeota [1]—contains ammonia-oxidizing archaea (AOA) as well as deeply rooted non-AOA [2,3]. AOA catalyze the first and the rate-limiting step of nitrification—the aerobic oxidation of ammonia to nitrate via nitrite [2]—and are the most abundant archaea in terrestrial and marine systems [4]. AOA are thought to be key members of the global nitrogen and carbon biogeochemical cycles [4–6]

Methods

Results

Conclusion