title: Direct conversion of plant biomass to ethanol by engineered Caldicellulosiruptor bescii.
abstract: Ethanol is the most widely used renewable transportation biofuel in the United States, with the production of 13.3 billion gallons in 2012 [John UM (2013) Contribution of the Ethanol Industry to the Economy of the United States]. Despite considerable effort to produce fuels from lignocellulosic biomass, chemical pretreatment and the addition of saccharolytic enzymes before microbial bioconversion remain economic barriers to industrial deployment [Lynd LR, et al. (2008) Nat Biotechnol 26(2):169-172]. We began with the thermophilic, anaerobic, cellulolytic bacterium Caldicellulosiruptor bescii, which efficiently uses unpretreated biomass, and engineered it to produce ethanol. Here we report the direct conversion of switchgrass, a nonfood, renewable feedstock, to ethanol without conventional pretreatment of the biomass. This process was accomplished by deletion of lactate dehydrogenase and heterologous expression of a Clostridium thermocellum bifunctional acetaldehyde/alcohol dehydrogenase. Whereas wild-type C. bescii lacks the ability to make ethanol, 70% of the fermentation products in the engineered strain were ethanol [12.8 mM ethanol directly from 2% (wt/vol) switchgrass, a real-world substrate] with decreased production of acetate by 38% compared with wild-type. Direct conversion of biomass to ethanol represents a new paradigm for consolidated bioprocessing, offering the potential for carbon neutral, cost-effective, sustainable fuel production.
authors.affiliation: Department of Genetics, University of Georgia, Athens, GA 30602; andThe BioEnergy Science Center and.
authors.forename: Daehwan
authors.initials: D
authors.lastname: Chung
authors.affiliation: Department of Genetics, University of Georgia, Athens, GA 30602; andThe BioEnergy Science Center and.
authors.forename: Minseok
authors.initials: M
authors.lastname: Cha
authors.affiliation: The BioEnergy Science Center andBiosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Guss
authors.affiliation: Department of Genetics, University of Georgia, Athens, GA 30602; andThe BioEnergy Science Center and janwest@uga.edu.
authors.forename: Janet
authors.initials: J
authors.lastname: Westpheling
mesh_terms: D000079:Acetaldehyde / Q000737:chemistry; D000426:Alcohol Dehydrogenase / Q000737:chemistry; D056804:Biofuels; D018533:Biomass; D048013:Acetivibrio thermocellus / Q000201:enzymology; D004736:Energy-Generating Resources; D000431:Ethanol / Q000737:chemistry*; D005285:Fermentation; D016937:Gram-Positive Endospore-Forming Rods / Q000737:chemistry*; D007770:L-Lactate Dehydrogenase / Q000737:chemistry; D008031:Lignin / Q000737:chemistry; D015202:Protein Engineering
chemical_list: D056804:Biofuels; C036909:lignocellulose; D000431:Ethanol; D008031:Lignin; D000426:Alcohol Dehydrogenase; D007770:L-Lactate Dehydrogenase; D000079:Acetaldehyde
keywords: bioenergy and thermophiles; metabolic engineering