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Applied and Environmental Microbiology, June 2005, p. 3213-3227, Vol. 71, No. 6
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.6.3213-3227.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Microbial Diversity in Ultra-High-Pressure Rocks and Fluids from the Chinese Continental Scientific Drilling Project in China

Department of Geology, Miami University, Oxford, Ohio 45056,¹ Chinese Academy of Geological Sciences, Institute of Geology, Beijing, China,² Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208,³ Savannah River Ecology Laboratory and Marine Sciences Department, University of Georgia, P.O. Box Drawer E, Aiken, South Carolina 29802⁴

Received 9 December 2003/ Accepted 16 December 2004

Microbial communities in ultra-high-pressure (UHP) rocks and drilling fluids from the Chinese Continental Scientific Drilling Project were characterized. The rocks had a porosity of 1 to 3.5% and a permeability of 0.5 mDarcy. Abundant fluid and gas inclusions were present in the minerals. The rocks contained significant amounts of Fe₂O₃, FeO, P₂O₅, and nitrate (3 to 16 ppm). Acridine orange direct counting and phospholipid fatty acid analysis indicated that the total counts in the rocks and the fluids were 5.2 x 10³ to 2.4 x 10⁴ cells/g and 3.5 x 10⁸ to 4.2 x 10⁹ cells/g, respectively. Enrichment assays resulted in successful growth of thermophilic and alkaliphilic bacteria from the fluids, and some of these bacteria reduced Fe(III) to magnetite. 16S rRNA gene analyses indicated that the rocks were dominated by sequences similar to sequences of Proteobacteria and that most organisms were related to nitrate reducers from a saline, alkaline, cold habitat; however, some phylotypes were either members of a novel lineage or closely related to uncultured clones. The bacterial communities in the fluids were more diverse and included Proteobacteria, Bacteroidetes, gram-positive bacteria, Planctomycetes, and Candidatus taxa. The archaeal diversity was lower, and most sequences were not related to any known cultivated species. Some archaeal sequences were 90 to 95% similar to sequences recovered from ocean sediments or other subsurface environments. Some archaeal sequences from the drilling fluids were >93% similar to sequences of Sulfolobus solfataricus, and the thermophilic nature was consistent with the in situ temperature. We inferred that the microbes in the UHP rocks reside in fluid and gas inclusions, whereas those in the drilling fluids may be derived from subsurface fluids.

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