Detection of the deep biosphere in metamorphic rocks from the Chinese continental scientific drilling.

Affiliation

Dai X(1)(2), Wang Y(1), Luo L(3), Pfiffner SM(4), Li G(1), Dong Z(1), Xu Z(5), Dong H(6), Huang L(1)(2).
Author information:
(1)State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
(2)College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China.
(3)National Research Center for Geoanalysis, Chinese Academy of Geological Sciences, Beijing, China.
(4)Center for Environmental Biotechnology, University of Tennessee, Knoxville, TN, USA.
(5)State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, China.
(6)Center for Geomicrobiology and Biogeochemistry Research, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing, China.

Abstract

It is generally accepted that there is a vast, well-populated biosphere in the subsurface, but the depth limit of the terrestrial biosphere has yet to be determined, largely because of the lack of access to the subsurface. Here as part of the Chinese Continental Scientific Drilling (CCSD) project in eastern China, we acquired continuous rock cores and endeavored to probe the depth limit of the biosphere and the depth-dependent distribution of microorganisms at a geologically unique site, that is, a convergent plate boundary. Microbiological analyses of ultra-high-pressure metamorphic rock cores taken from the ground surface to 5,158-meter reveal that microbial distribution was continuous up to a depth of ~4,850 m, where temperature was estimated to be ~137°C. The metabolic state of these organisms at such great depth remains to be determined. Microbial abundance, ranging from 103 to 108  cells/g, was also related to porosity, but not to the depth and rock composition. In addition, microbial diversity systematically decreased with depth. Our results support the notion that temperature is a key factor in determining the lower limit of the biosphere in the continental subsurface.