S198: Improving Lignocellulose Degradation with Thermostable Enzymes

It is obvious that extremophiles and their enzymes are likely to play important roles in many kinds of bioprocessing (e.g., conversion of non-food biomass into biofuels including bioethanol, biodiesel, biobutanol, and biogas).  Much attention has been paid to thermophilic bioprocessing of lignocellulosic biomass to biofuels as it offers several potential advantages.  Current technologies for sustainable and economical processing of lignocellulose into biofuels are limited due to high production costs of lignocellulose-hydrolyzing enzymes; slow enzymatic hydrolysis kinetics of releasing sugars from lignocellulose; and the low yields of sugars.  These issues can be addressed using enzymes and organisms naturally adapted to environments of extreme temperature.  We have been working on extremophiles from the deepest mine - the Homestake Gold Mine, SD and a local compost facility for lignocellulose conversion under thermophilic (≥60^oC) conditions.  Using deep biosphere and compost facility soil samples, we have isolated several thermophilic cellulose- and xylan-degrading pure cultures belonging to the genera Paenibacillus, Bacillus, and Geobacillus.  Unique characteristics of cellulases and xylanases produced by DUSEL and compost thermophiles include optimum temperatures of >70°C, pH of 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).  DUSEL and compost thermophiles also grew on various inexpensive regional carbon and energy sources (e.g., prairie cordgrass, corn stover).  These thermostable enzymes and robust thermophilic fermentative microbes will facilitate development of more efficient and cost-effective forms of the simultaneous saccharification and fermentation process to convert lignocellulosic biomass into biofuels.