1-21: Consolidated bioprocessing capabilities of Clostridium thermocellum, Caldicellulosiruptor obsidiansis, and Caldicellulosiruptor bescii on dilute acid pretreated Populus biomass

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Kelsey Yee, Miguel Rodriguez Jr., Choo Hamilton, Scott Hamilton-Brehm and Jonathan Mielenz, Biosciences Division and BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN
Economic feasibility of converting lignocellulosic biomass to a liquid fuel could be improved through the use of CBP, which comprises fermentative microorganisms that produce some or all of the needed biomass hydrolytic enzymes. In this study, we evaluate the fermentation capabilities of three very active CBP microorganisms, Clostridium thermocellum, Caldicellulosiruptor bescii, and Caldicellulosiruptor obsidiansis on a consistent substrate and uniform media. C. obsidiansis and C. bescii fermentations took approximately twice as long as C. thermocellum. Metabolite analysis of fermentations with C. bescii and C. obsidiansis produced primarily acetic acid, minimal lactic acid, and essentially no ethanol with C. obsidiansis out performing C. bescii in terms of total product formation and yield on utilized substrate (0.46 g/g and 0.35 g/g, respectively). C. thermocellum fermentations produced acetic acid, ethanol, and minimal lactic acid with an acetic acid to ethanol ratio of 2.9 and an overall yield of 0.39 g/g utilized substrate. The results from the quantitative saccharification assay of fermentation residues showed that the enzymes produced by C. bescii and C. obsidiansis were simultaneously hydrolyzing hemicellulose and cellulose at the same rate. The results for fermentations with C. thermocellum showed that the cellulosome was hydrolyzing primarily cellulose at a rate that was approximately 2.6 times greater than the Caldicellulosiruptor strains. The CBP microorganisms did not fully hydrolyze the substrate leaving fermentable carbohydrates and as a result, C. bescii, C. obsidiansis, and C. thermocellum fermentations reached respectively an average 74% ± 9, 91% ± 7, and 78% ± 2 of theoretical carbohydrate conversion.
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