8-7 Understanding sugar yield loss and enzyme inhibition due to oligosaccharides accumulation during high solids-loading enzymatic hydrolysis
Tuesday, April 28, 2015: 3:35 PM
Aventine Ballroom DEF, Ballroom Level
Saisi Xue1, Nirmal Uppugundla2, Michael J. Bowman3, Mingjie Jin4, Leonardo da Costa Sousa5, Shishir P.S. Chundawat2, Brian Fox6, David Cavalier7, Bruce E. Dale8 and Venkatesh Balan9, (1)Department of Chemical Engineering and Materials Science, Michigan State University, DOE Great Lakes Bioenergy Research Center (GLBRC), East Lansing, MI, (2)Biomass Conversion Research Laboratory, Deparment of Chemical Engineering and Materials Science, DOE Great Lakes Bioenergy Research Center, Michigan State University, Lansing, MI, (3)Bioenergy Research Unit, United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, IL, (4)Chemical Engineering and Materials Science, Michigan State University, DOE Great Lakes Bioenergy Research Center, Lansing, MI, (5)Department of Chemical Engineering and Materials Science,, Michigan State University and University of Pune, Lansing, MI, (6)Department of Biochemistry, University of Wisconsin-Madison, DOE Great Lakes Bioenergy Research Center, Madison, WI, (7)DOE Plant Research Laboratory, Michigan State University, East Lansing, MI, (8)Chemical Engineering and Materials Science, DOE Great Lakes Bioenergy Research Center, Michigan State University, Lansing, MI, (9)Department of Chemical Engineering and Materials Science, Michigan State University, DOE Great Lakes Bioenergy Research Center, Lansing, MI
During enzymatic hydrolysis of biomass, polysaccharides are cleaved by glycosyl hydrolases to soluble oligosaccharides and further hydrolyzed by β-glucosidase, β-xylosidase and other enzymes to monomeric sugars. However, not all oligosaccharides can be fully hydrolyzed and they may accumulate to 18-25% of the total soluble sugars at high solid loading (>3-25% solids loading). Oligosaccharide accumulation reduces ethanol yields because industrial ethanol-producing strains only consume monomeric sugars. Very little is understood about the nature of these oligomers and why they accumulate. In this work, we report a large-scale, robust method to separate and produce recalcitrant oligosaccharides using affinity-based charcoal fractionation and molecular weight-based gel filtration chromatography from high solids-loading AFEX-corn stover (ACS) hydrolysate. The low DP (degree of polymerization)  oligosaccharides can be digested using commercial enzyme mixtures (Ctec2, Htec2 and Multifect pectinase(MP)) after being separated from the hydrolysate, while the high DP oligosaccharides were highly recalcitrant. Inhibition studies using pure substrates (Avicel and beechwood xylan) showed that low DP oligosaccharides are highly inhibitory to commercial enzymes, and the addition of monomeric sugars further intensified the inhibition. Chemical structures of oligosaccharides with varying DP, composition of monomeric sugars, and the extent of branching patterns have also been identified by acid hydrolysis, methylate derivatization, LC-MS and NMR. Using these oligosaccharides as substrates, enzymes and microbes arrays were screened to identify candidates to break down the un-hydrolyzed crosslinks and digest the oligosaccharides completely. This work helps us understand the mechanisms behind oligosaccharides accumulation and thus develop better strategies to increase sugar yields during biomass hydrolysis.
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