Tuesday, August 14, 2012: 3:00 PM
Jefferson East, Concourse Level (Washington Hilton)
Consolidated bioprocessing (CBP) conversion comprises biomass fermentative microorganisms that produce some or all of the needed biomass hydrolytic enzymes, mitigating the cost of added enzymes. It has been shown previously that down-regulation of the caffeic acid O-methyltransferase (COMT) gene in switchgrass (Panicum virgatum) reduced lignin content, reduced S/G ratio, increased sugar release, and improved the yeast-based SSF conversion of the modified switchgrass line compared to the control. To follow-up this work, we examined the fermentation of both control and COMT transgenic switchgrass lines using CBP anaerobic bacteria including Clostridium thermocellum, Caldicellulosiruptor bescii, and Caldicellulosiruptor obsidiansis. A differential of inhibition was shown for C. thermocellum fermentations of dilute acid pretreated switchgrass with the control outperforming the transgenic. However, full fermentation capabilities for C. thermocellum were restored after an extra hot water extraction of soluble components from the control and transgenic switchgrass. The COMT line yielded about 25% more total products than from the control. However, using the same biomass sources processed identically with extensive water extraction, C. obsidiansis and C. bescii failed to ferment the transgenic switchgrass (ca. 7-10% of expected) while successfully fermenting the control switchgrass lines and intermediate transgenic T1-COMT12. The high degree of inhibition led to the selection of a transgenic T1-COMT3-tolerant mutant of C. obsidiansis that restored expected fermentation yields with transgenic switchgrass