HR: 15:24h
AN: V13C-09    [Abstracts]
TI: Microbial Communities in Ultra-High Pressure Rocks and Fluids From Chinese Continental Scientific Drilling (CCSD): A Unique Opportunity to Study Microbial Adaptation and Survival
AU: * Dong, H
EM: dongh@muohio.edu
AF: Miami University, Department of Geology, Oxford, OH 45056 United States
AU: Zhang, G
EM: zhangg@muohio.edu
AF: Miami University, Department of Geology, Oxford, OH 45056 United States
AU: Xu, Z
EM: xuzhiqin@ccsd.org.cn
AF: Chinese Academy of Geological Sciences, Key Laboratory for Continental Dynamics (KLCD), Institute of Geology, 26 Baiwanzhuang Road, Beijing, 100037 China
AB: A major obstacle to understanding the subsurface biosphere has been our limited ability to access the deep subsurface, to acquire uncontaminated samples and to place our knowledge of isolated microorganisms into environmental context. We studied deep subsurface microbiology by taking an advantage of the Chinese continental scientific drilling (CCSD) project currently underway in China. The project is to drill a 5-km deep borehole in the Dabie-Sulu ultra high-pressure (UHP) metamorphic belt in China that is located at the convergent plate boundary between Sino-Korean and Yangtze Plate. The collision began at ~240 Ma ago followed by exhumation ~220 Ma ago. The products of such a plate convergence are the formation of unique UHP rocks and minerals. These rocks are typically separated by a series of structurally weak shear zones and faults. The macroscopic shear zones/faults are potential storage space for large pockets of fluids/gases and they may serve as a potential microbial habitat. Fluids/gas bubbles also exist inside minerals, and they are called fluid/gas inclusions. The inclusions are microscopic and they serve as another potential habitat for microbes. The 5-km contiguous drilling intercepts both habitats and spans a range of environmental gradients. Our cultivation and SSU rRNA gene analyses appear to indicate that unique microbial communities may exist in both habitats. A variety of methods were used to assess possible contamination, and contamination was minimal. Acridine orange direct count method was employed to determine the total number of cells in the rocks, and the results indicated that the biomass ranged from 5.2 x 103 to 2.4 x 104 cells/g (dry weight). Total counts indicated a much higher biomass in the drilling fluids, ranging from 3.5 x 108 to 4.2 x 109 cells/g (wet weight). The PLFA profiles for one rock and multiple drilling fluids indicated the presence of sulfate and metal reducers. Cultivation attempts have identified the presence of mesophilic Fe(III) reducers in the rocks, but thermophilic (37 to 68oC) and alkaliphilic metal reducers and fermenters in the drilling fluids. SSU rRNA gene analyses detected clone sequences in the rocks that have previously been isolated from cold, alkaline and saline environments (including mesophilic, facultative, heterotrophic, halotolerant or halophilic nitrate and Fe(III) reducers). These microbial growth habitats are inconsistent with the present day geochemical conditions (geothermal gradient, for example). We speculate that these microbes reside in mineral fluid/gas inclusions. Because the inclusions are isolated and heat conductivity is low, microenvironment inside the inclusions may be out of equilibrium with the bulk subsurface conditions. The microbial communities in the drilling fluids include anaerobic, alkaliphilic, chemoorganotrophic or chemolithoautotrophic, halotolerant or halophilic Fe(III) and sulfate reducers, fermenters, acetogens, and methanogens/methanotrophs. This microbial growth habitat suggests that the detected microbes in the drilling fluids may be of different origin, and they may be derived from macroscopic fluids/gases associated with structurally weak shear zones/faults. Because of possible connectivity to flow channels and shear zones, these fluids/gases may be in equilibrium with the in-situ subsurface conditions, and microbes from this habitat are expected to change in environmental gradients.
DE: 4840 Microbiology
DE: 0400 Biogeosciences
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting