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Capture of Planktonic Microbial Diversity in Fractures by Long-Term Monitoring of Flowing Boreholes, Evander Basin, South Africa

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The diversity of planktonic microorganisms in fluids from a group of flowing subterranean boreholes was monitored from the day they were drilled to as long as three and a half months after drilling as they drained into Evander Au mine. Geochemical analyses of the water, characterization of microbial communities by phospholipids fatty acid (PLFA) and DNA sequence analyses, and calculations of free energy flux indicated that mine-introduced microbial contaminants, dominated by β and γ Proteobacteria, Cenarchaeaceae and Candidatus Nitrososphaera, were flushed from the boreholes and replaced by fracture water derived microbial communities dominated by Firmicutes, Methanosarcinalesand Thermoproteaceaea. The fracture water was a mixture of paleometeoric water and 2.0 Ga old, diagenetically altered, hydrothermal fluid. The C and H isotopic data for C1-4 indicated that the CH4 was primarily abiogenic in origin although ∼35-50% of it might have originated from microbial methanogenesis. Noble gas analyses yielded estimated residence times of some 10 million years for the fracture water, which is estimated to represent a capture cross-section of 0.25-0.50 km2. The 16S rRNA and dsrAB gene sequences indicated that the indigenous bacterial communities were predominantly comprised of sulfate reducers belonging to the genera Desulfotomaculum, Candiditus Desulforudis and Desulfofustis. The sulfur isotopic analyses of sulfate and sulfide yielded fractionation Δ34S values ranging from 16 to 22% consistent with microbial sulfate reduction. Thermodynamic analyses indicate that methanogenic reactions are inhibited by the high partial pressure of abiogenic CH4 and that sulfate-reducing reactions are more favorable, which is consistent with the abundance of 16S rRNA genes belonging to known sulfate reducing bacteria. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.

Keywords: 16S rRNAphylogeny; dsrAB; isotope geochemistry; methanogenesis; sulfate reduction

Document Type: Research Article


Affiliations: 1: Department of Geosciences, Princeton University, Princeton, New Jersey, USA,Geosyntec, Pasadena, California, USA 2: Department of Geosciences, Princeton University, Princeton, New Jersey, USA 3: Environmental Microbiology Group, Pacific Northwest National Laboratory, Richland, Washington, USA,Division of Earth and Ecosystems Sciences, Desert Research Institute, Las Vegas, Nevada, USA 4: Environmental Microbiology Group, Pacific Northwest National Laboratory, Richland, Washington, USA,Biosciences Division, Oak Ridge National Laboratory, Microbial Ecology and Physiology Group, Oak Ridge, Tennessee, USA 5: Department of Geology, Indiana University, Bloomington, Indiana, USA 6: Department of Geology, Indiana University, Bloomington, Indiana, USA,ExxonMobil Research and Engineering, Houston, Texas, USA 7: Department of Geology, University of Toronto, Toronto, Ontario, Canada 8: Institute of Radiochemistry, Forschungszentrum Dresden Rossendorf - Research Site Leipzig, Leipzig, Germany 9: Center of Biomarker Analysis, University of Tennessee, Knoxville, Tennessee, USA 10: Department of Biology, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA 11: Geology Department, Evander Mine, Harmony Gold Mining Company Ltd., South Africa

Publication date: 2011-05-01

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