Sunday, May 3, 2009
6-11
Characterization of extremophilic cellulose-degrading bacteria from the deep subsurface of the Homestake gold mine, Lead, South Dakota, USA
Gurdeep Rastogi1, Geetha Muppidi1, Raghu Gurram2, Akash Adhikari1, Sookie Bang1, Lew Christopher3, Kenneth M. Bischoff4, Stephen R. Hughes5, William Apel6, and Rajesh K. Sani7. (1) South Dakota School of Mines, 501 E. St. Joseph St., Rapid City, SD 57701, (2) Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, 501 East St. Joseph Street, Rapid City, SD 57701, (3) Center for Bioprocessing Research and Development, South Dakota School of Mines and Technology, 501 East Saint Joseph Street, Rapid City, SD 57702-3995, (4) National Center for Agricultural Utilization Research, USDA - Agricultural Research Service, 1815 N. University St., Peoria, IL 61604, (5) Bioproducts and Biocatalysis Research Unit, United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural, 1815 North University Street, Peoria, IL 61604, (6) Biological Sciences, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415, (7) Department of Chemical and Biological Engineering and CBRD, South Dakota School of Mines and Technology, 501 East Saint Joseph Street, Rapid City, SD 57701
Ligninocellulosic materials are among the Earth's most abundant renewable resources. The degradation of cellulosic waste materials with greater rates by high potential microbes (e.g., thermophiles) is very important. Therefore, the present study investigated the cultivable mesophilic (37ºC) and thermophilic (60ºC) cellulose-degrading bacterial diversity in a weathered soil-like sample collected from the deep subsurface (1.5 km depth) of the Homestake gold mine in Lead, South Dakota , USA . Molecular community structures were determined by phylogenetic analysis of 16S rRNA gene sequences retrieved from enrichment cultures growing in presence of microcrystalline cellulose as the sole source of carbon. All phylotypes retrieved from enrichment cultures were affiliated to Firmicutes. Cellulose-degrading mesophilic and thermophilic pure cultures belonging to the genera Brevibacillus, Paenibacillus, Bacillus, and Geobacillus were isolated from enrichment cultures, and selected cultures were studied for enzyme activities. For a mesophilic isolate (DUSELG12), the optimum pH and temperature for carboxymethyl cellulase (CMCase) were 5.5 and 55ºC, while for a thermophilic isolate (DUSELR7) they were 5.0 and 75ºC, respectively. Furthermore, DUSELG12 retained about 40% CMCase activity after incubation at 60ºC for 8 hours. Most remarkably, thermophilic isolate, DUSELR7 retained 26% CMCase activity at 60ºC up to a period of 300 hours. Overall, the present work revealed the presence of different cellulose-degrading bacterial lineages in the unique deep subsurface environment of the mine. The results also have strong implications for biological conversion of cellulosic agricultural and forestry wastes to commodity chemicals including sugars.