S75: Presence of high-value microbes and microbial enzymes in the deep biosphere of the former Homestake gold mine, South Dakota

The Homestake gold mine (8000 ft. deep, Lead, SD) offers a unique opportunity for direct exploration of the deep biosphere environment. This mine is now known as the Sanford Underground Research Facility -SURF. In past six years, we have obtained water, soil, and sediment samples from the 300, 2000, 4400, 4850, and 5000 ft. levels. Using PhyloChips, clone libraries, and various enrichments results show that SURF harbors a significant microbial diversity including archaea, unclassified (novel) microbes, and unique organic polymer-degrading and -fermentative bacteria. SURF microbial diversity compared well at phylum level with other gold mines. The common bacterial phyla were Acidobacteria, Actinobacteria, Bacteroidetes, Chlorobi, Chloroflexi, Firmicutes, Gemmatimonadetes, Nitrospirae, Proteobacteria, and candidate divisions OP10 and TM7. However, specific lineages within phyla, such as the presence of genera e.g., Rheinheimera, Zobellella, and Devosia in the SURF have not been documented in any earlier studies from the deep subsurface gold mines. We also found the presence of Verrucomicrobia which has not been documented for other gold mines. Using various enrichments, we have isolated several thermophilic cellulose- and xylan-degrading pure cultures belonging to the genera Brevibacillus, Clostridium, Paenibacillus, Bacillus, and Geobacillus.  Unique characteristics of cellulases and xylanases produced by mine thermophiles include optimum temperatures of >70°C, pH ranges from 4 - 8, and high thermostability.  We are currently trying to elucidate the structure-function relationship of these thermostable enzymes and the structural factors that leads to their thermostability.  This fundamental information will be critical in developing a more efficient and cost-effective biofuel production process.