(374af) Thermophilic Microbes and Their Thermostable Enzymes for Lignocellulose Conversion

Authors: 
Sani, R. K., South Dakota School of Mines & Technology
Bhalla, A., South Dakota School of Mines & Technology
Kunreddy, V., South Dakota School of Mines & Technology
Zambare, V., South Dakota School of Mines & Technology
Bischoff, K., USDA-ARS, NCAUR
Dixon, D., SD School of Mines and Technology
Christopher, L. P., South Dakota School of Mines & Technology


The literature suggests that current strategies for sustainable and economical processing of lignocellulose into biofuels is limited due to high production costs of lignocellulose-hydrolyzing enzymes; the very slow enzymatic hydrolysis kinetics of release of sugars from lignocellulose; and the low yields of sugars from lignocellulose. These issues can be addressed using enzymes and organisms naturally adapted to environments of extreme temperature. At high temperatures, bioreactors can offer faster, more effective and reliable conversion of substrates to commodity chemicals due to increased solubility and hydrolysis of lignocelluloses as well as a lower potential for contamination. Our group has been working on extremophiles from the deepest mine (2.5 km deep) - the Homestake Gold Mine, Lead, SD (also known as NSF DUSEL) and from a local compost facility for lignocellulose conversion under thermophilic (≥60oC) conditions. Using deep subsurface (1.34 km) and compost facility soil samples, we have isolated several thermophilic cellulose- and xylan-degrading pure cultures belonging to the genera Brevibacillus, Paenibacillus, Bacillus, and Geobacillus. Unique characteristics of DUSEL cellulases and xylanases include optimum temperatures of >70°C, pH ranges from 4 - 8, and high thermostability (e.g., at 60ºC, 50% of cellulases and xylanases activities were lost in 35 and 23 days of incubation, respectively). In addition, DUSEL thermophiles grew on various carbon sources and produced ethanol from cellulose in a single step. These thermostable enzymes and robust thermophilic fermentative microbes should facilitate development of more efficient and cost-effective forms of the simultaneous saccharification and fermentation process to convert lignocellulosic biomass into biofuels.