South African Ultradeep Mines-Long Term Sites for Interdisciplinary Studies (LSLIS) into the Extreme Environment of the Deep Subsurface

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9978267Onstott Recent investigations have identified microbial communities in various crustal environments down to 3.2 kilometers below the surface (kmbls.). Only a hand full of deep microbial samples from continental crust (0.5 kmbls.) exist, however, because coring is expensive. In the fall of 1998, an expedition of scientists from the USA, Canadian, and Swedish universities and U.S. DOE National labs searched the rock strata and groundwater of the ultradeep Au mines of South Africa for microorganisms. The goal of this research was to determine whether these mines, which extend 3 kmbls., offer ready access to indigenous, subsurface microbial communities and whether radiolysis of groundwater provides a nutrient source for the microorganisms. Rock, water and biofilm samples were collected from several of these mines at depths ranging from 0.8 to 3.2 kmbls. Preliminary results indicate that a variety of thermophilic microorganisms are present in the groundwater and rock. Some of these microorganisms represent novel species, radiation tolerant and appear uniquely adapted to the geochemical and hydrological crustal environment from which they were derived. Furthermore, evidence indicates that most of these microorganisms are autochthonous and not simply the result of contamination. PIs plan to establish a 5 year observation and sample acquisition program to analyze the microbial communities in the deep continental lithosphere of South Africa and address the following hypotheses, which are critical to gaining insight into potential exobiological niches and into how microorganisms can adapt and survive in relatively extreme environments. 1. Do autotrophic microbial communities dominate over heterotrophic communities in the deep subsurface?2. Are there deep subsurface microbial communities that are self-sufficient in terms of their energy and catabolic resources or do they all ultimately rely upon organic constituents supplied from the present surface biosphere or ancient buried fossil fuels?3. Are the cell lifetimes on the order of centuries as suggested by geochemical estimates of subsurface microbial activity and, if so, are these rates compatible with long term survival under low levels of ionizing radiation?4. Are microbial communities present in fluid fractures functionally and phylogenetically distinct from those present within the rock matrix.To address the above research hypotheses, PIs will improve enrichment, culturing and isolation technologies, in the detection limits for and rapidity of PLFA and DNA analyses, and develop instruments for quantifying in situ microbial activity within deep boreholes.