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

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          Abstract

          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 (≤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.

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          Author and article information

          Journal
          Proceedings of the National Academy of Sciences
          Proc Natl Acad Sci USA
          Proceedings of the National Academy of Sciences
          0027-8424
          1091-6490
          March 01 2011
          March 01 2011
          March 01 2011
          February 14 2011
          : 108
          : 9
          : 3803-3808
          Article
          10.1073/pnas.1100310108
          1fb9204f-afdf-436d-bed7-b902688a1800
          © 2011
          History

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