Saccharification of thermochemically pretreated cellulosic biomass using native and engineered cellulosomal enzymes
Using microbes like Clostridium thermocellum for consolidated bioprocessing of biomass enables one-pot production of fuels
Pretreating lignocellulosic biomass using microbes such as C. thermocellum enables a one-pot process for breaking down sugars and fermenting those sugars for fuel and chemicals. In this study, we examined the bacterium’s efficiency in breaking down cellulose in industrially relevant pretreated biomass, finding that pretreatments that remove both lignin and hemicellulose can help improve the specific activity of the bacterium’s cellulosomal enzymes.
Our research on C. thermocellum, a bacterium that deconstructs biomass using large, multi-enzyme complexes called cellulosomes, provides insight into how to overcome the challenge of deconstructing lignocellulosic-derived sugar polymers, and may lead to the more efficient and cost-effective use of cellulosic biomass in making fuels and chemicals.
Researchers in the Great Lakes Bioenergy Research Center compared the hydrolytic activity of the most abundant cellulosomal enzymes from C. thermocellum and investigated the importance of enzyme complexation using a model engineered protein scaffold called a “rosettasome.” We tested the hydrolytic performance of non-complexed enzymes, enzyme-rosettasome/rosettazyme complexes, and cellulosomes on distinct cellulose allomorphs formed during pretreatment of biomass. The scaffold-immobilized enzymes always gave higher activity than the free enzymes; however, cellulosomes exhibited higher activity than rosettazyme complexes. This was likely due to the greater flexibility of the native versus engineered scaffold, as deciphered using small angle X-ray scattering. Scaffold-tethered enzymes gave lower saccharification yields on industrially relevant lignin-rich switchgrass than cellulose alone, as well as comparable activity on all the cellulose allomorphs tested. These results indicate that the type of pretreatment can significantly impact the saccharification efficiency of cellulosomal enzymes for various consolidated bioprocessing scenarios, and pretreatments that remove both lignin and hemicellulose can help improve the specific activity of cellulosomal enzymes.
Contacts (BER PM)
N. Kent Peters
Program Manager, Office of Biological and Environmental Research
Bruce E. Dale
Michigan State University
This study was funded by NASA Ames Research Center and Michigan State University Research Foundation. We also acknowledge partial support by the National Science Foundation Grant #1236120 (CBET – Energy for Sustainability) and the DOE Great Lakes Bioenergy Research Center (supported by the Department of Energy, Office of Science, Office of Biological and Environmental Research, through Cooperative Agreement DE-FC02-07ER64494 between The Board of Regents of the University of Wisconsin System and the Department of Energy; www.glbrc.org). BR and JRM were supported through the BioEnergy Science Center (BESC). BESC is a U.S. Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. Oak Ridge National Laboratory is managed by UTBattelle LLC for the US DOE under contract number DE-AC05-00OR22725.
Chundawat, S. P. S., et al. (2016). "Saccharification of thermochemically pretreated cellulosic biomass using native and engineered cellulosomal enzyme systems." Reaction Chemistry & Engineering 1(6): 616-628. DOI: 10.1039/C6RE00172F