1-20: Towards industrial robustness: comparison of wild-type and Populus hydrolysate-tolerant mutant strains of Clostridium thermocellum

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Jessica L. Linville1, Miguel Rodriguez2, Jonathan R. Mielenz2 and Chris D. Cox1, (1)Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN, (2)Biosciences Division and BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN
An industrially robust microorganism capable of degrading lignocellulosic biomass in the presence of inhibitory compounds produced from the pretreatment process in a CBP scheme is needed to reduce the cost of cellulosic biofuels. Clostridium thermocellum has the ability to convert biomasses complex carbohydrates into ethanol by fermentation. However, C. thermocellum is inhibited by by-products from the biomass pretreatment process. To increase C. thermocellum’s industrial robustness, a 17.5% v/v Populus hydrolysate-tolerant mutant (PM) was produced by 117 successive transfers of C. thermocellum 27405 strain into increasing concentrations of the hydrolysate. A single colony culture of the PM was then produced and the genome is being sequenced. A study comparing the wild-type (WT) and PM strains of C. thermocellum was completed with growth on cellobiose examining sugar utilization and end product formation, and growth on Avicel examining protein concentration. The growth of the PM in 17.5% v/v Populus hydrolysate had a 20% higher optical density, a 33% faster sugar utilization rate (g glucan/L/hr), and produced 34% more ethanol (g ethanol/ g glucan) than the WT grown without hydrolysate. The PM retained these characteristics when grown without hydrolysate with a 37% higher optical density, a 40% faster sugar utilization rate and produced 20% more ethanol than the WT grown under the same conditions. The WT was severely inhibited when grown in the presence of 17.5% v/v Populus hydrolysate with a barely detectable optical density, 7% of sugar utilization rate, and produced 7.5% of the expected ethanol versus when it was grown without hydrolysate. 
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