Monday, April 19, 2010
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Native corn stover induces efficient production of hydrogen and ethanol in Clostridium thermocellum

Hui Wei1, Lauren Magnusson1, Melvin Tucker2, John Baker1, Igor Bogorad1, Andrew Bowersox1, Yining Zeng1, Yu-San Liu1, Yonghua Luo1, Michael Himmel1, Pin-Ching Maness1, and Shi-You Ding1. (1) Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd. (MS-3323), Golden, CO 80401, (2) National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd. (MS-3323), Golden, CO 80401

The anaerobic thermophilic bacterium Clostridium thermocellum produces a multiprotein cellulosomal enzyme system that is believed to have higher activity than the fungal free enzyme systems on deconstructing complex plant cell wall biomass, and could be used potentially for processing biomass to biofuels.  The bacterium also produces hydrogen and ethanol as products that could be used in direct biofuel production. This study uses different forms of corn stover (either dilute-acid-pretreated or merely milled), as representative biomass-derived growth substrates and inducers in C. thermocellum fermentation.  We have found that cumulative production of H2, ethanol, as well as cellulosomal enzymes are correlated with the mass balances of the cellulose and hemicellulose components of the biomass during fermentation, which in turn provide estimates of the efficiency of C. thermocellum in utilizing the biomass as growth substrate. Transcriptomic analysis of genes encoding the various components of cellulosomes is employed to identify the genes that are responsive to induction by different growth substrates.  The hydrolytic properties of produced cellulosomes are characterized by their activities on Avicel and three “nearly natural” substrates - corn stover, switchgrass and yellow poplar.  The results highlight the distinct superiority of the cellulosomes induced by untreated vs. acid-treated corn stover in the degradation of “natural” biomass substrates, whereas only a small difference is noted between the two enzyme preparations when assayed against the Avicel cellulose.  These comprehensive experiments yield insights into the dynamics of bacterial growth, biomass consumption and production of cellulosomal enzyme components, which will enable a multiple-products strategy to improve the economy of biofuels technology. 

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