Journal Article

Genetic manipulation of lignin reduces recalcitrance and improves ethanol production from switchgrass

Rodriguez, Miguel Jr, Ge, Yaxin, Mielenz, Jonathan R, Chen, Fang, Ragauskas, Arthur, Fu, Chunxiang, Wang, Zeng-Yu, Hamilton, Choo Y, Xiao, Xirong, Dixon, Richard A, Bouton, Joseph, Foston, Marcus

2011

Overview

Switchgrass is a leading dedicated bioenergy feedstock in the United States because it is a native, high-yielding, perennial prairie grass with a broad cultivation range and low agronomic input requirements. Biomass conversion research has developed processes for production of ethanol and other biofuels, but they remain costly primarily because of the intrinsic recalcitrance of biomass. We show here that genetic modification of switchgrass can produce phenotypically normal plants that have reduced thermal-chemical ([less-than or equal to]180 °C), enzymatic, and microbial recalcitrance. Down-regulation of the switchgrass caffeic acid O-methyltransferase gene decreases lignin content modestly, reduces the syringyl:guaiacyl lignin monomer ratio, improves forage quality, and, most importantly, increases the ethanol yield by up to 38% using conventional biomass fermentation processes. The down-regulated lines require less severe pretreatment and 300-400% lower cellulase dosages for equivalent product yields using simultaneous saccharification and fermentation with yeast. Furthermore, fermentation of diluted acid-pretreated transgenic switchgrass using Clostridium thermocellum with no added enzymes showed better product yields than obtained with unmodified switchgrass. Therefore, this apparent reduction in the recalcitrance of transgenic switchgrass has the potential to lower processing costs for biomass fermentation-derived fuels and chemicals significantly. Alternatively, such modified transgenic switchgrass lines should yield significantly more fermentation chemicals per hectare under identical process conditions.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Bacteria / Biofuels / Biofuels - analysis / Biological Sciences / Biomass / Biomass production / caffeate O-methyltransferase / caffeic acid O-methyltransferase / Cellulase / Cellulase - metabolism / Chemicals / Clostridium thermocellum / Down-Regulation - genetics / endo-1,4-beta-glucanase / Energy crops / Enzymes / Ethanol / Ethanol - metabolism / ethanol production / feedstocks / Fermentation / forage quality / Fuel technology / Fuels / gene expression regulation / genes / genetic engineering / Genetic Techniques / genetically modified organisms / Genetics / Genotype & phenotype / Grasses / Hydrolysis / Lignin / Lignin - genetics / Methyltransferases - genetics / Molecular Sequence Data / Monomers / Panicum - enzymology / Panicum - genetics / Panicum - growth & development / Panicum - metabolism / Panicum virgatum / Phenotype / Plants / Plants, Genetically Modified / Prairies / Pretreatment / saccharification / Transgenic plants / United States / Yeast / Yeasts