Monday, April 19, 2010
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Properties of thermostable cellulose-degrading enzymes of deep underground thermophilic isolates

Aditya Bhalla1, Vasudeo Zambare1, Patrick C. Gilcrease2, Rajesh Sani1, and Lew Christopher1. (1) Center for Bioprocessing Research and Development, South Dakota School of Mines and Technology, 501 East Saint Joseph Street, Rapid City, SD 57702-3995, (2) Dept. of Chemical and Biological Engineering, South Dakota School of Mines and Technology, 501. E. St. Joseph Street, Rapid City, SD 57701

Lignocellulosic biomass is the most abundant and renewable organic raw material in the world. Biomass utilization could allow the development of self-sustainable processes for the production of energy, food, feed and chemicals. However, biomass recalcitrance to enzymatic breakdown is one of the major obstacles that need to be overcome for the establishment of cost-effective bioprocesses. The use of thermostable cellulose-degrading enzymes would greatly enhance hydrolysis and mass transfer rates of biomass degradation. The present study reports on the microbial production and characterization of cellulolytic enzymes of a thermophilic bacterial Geobacillus sp. isolated from the deep underground subsurface of the former Homestake mine in Lead, SD. The impact of various lignocellulosic feedstocks on the cellulase secretion by the Geobacillus isolate was examined in a 2L fermentor. Maximum cellulase production (154 U/L) was obtained with pretreated corn stover in a Nitsch’s medium at pH 7.0, 60¢ªC, 150 rpm agitation after 6 days of incubation. The thermophilic isolate produced 2.1-fold and 7-fold more cellulase activity when grown on pretreated corn stover than cellulose and untreated corn stover, respectively. The optimum pH and temperature for the crude cellulase were found to be pH 5 and 750C, respectively, whereas its half life at 600C was 8 days. The enzyme activity was enhanced 17% by Mg++ but completely inhibited with Cu++ and Zn++. Results warrant further investigations to evaluate the potential of the thermostable Geobacillus cellulase in a separate hydrolysis and fermentation as well as simultaneous saccharification and fermentation of lignocellulosic substrates for efficient bioethanol production.

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