Friday, July 17th, 2015
1:10 PM, 2045 Bainer Hall
"A Biochemical Route for the Production of Fuels and Chemicals from Cellulosic Biomass"
Amanda Hildebrand
Abstract:
Cellulosic biomass is an attractive resource for biofuel and chemical production due to its widespread availability, distinction from food crops, and low cost. Fuels derived from cellulosic biomass have significant potential to reduce dependence on foreign oil, lower greenhouse gas emissions, and drive economic development. Despite these benefits, commercialization has been impeded by the high production costs associated with overcoming the recalcitrance of cellulose. The conventional process for fuel and chemical production from cellulosic biomass involves five key steps: pretreatment, cellulase production, enzymatic hydrolysis, fermentation, and product recovery. Consolidating the process into fewer processing steps is one way to improve the overall economics. Utilizing lignocellulolytic microorganisms to directly hydrolyze the cellulose into reactive intermediates, such as sugar or sugar-like compounds, for subsequent conversion to fuels or chemicals is one such way to consolidate the process.
In the proposed biological process, Neurospora crassa, a cellulolytic fungus, is used as a model organism to convert cellulose to aldonic acids, primarily cellobionic acid. A previously engineered strain of N. crassa (F5) with six out of seven bgl genes knocked out was shown to produce cellobiose and cellobionate directly from cellulose without the addition of exogenous cellulases. The F5 strain was further modified to improve the yield of cellobiose and cellobionate from cellulose by increasing cellulase production and minimizing product consumption. The carbon flow was further directed to the production of cellobionate by oxidizing cellobiose with cellobiose dehydrogenase (CDH). The conversion reaction was optimized by adding low concentrations of laccase and a redox mediator to the fermentation, with efficient re-oxidation of CDH by the redox mediator and in-situ re-oxidation of the redox mediator by laccase. The resulting process achieves over 90% yield of cellobionate from the hydrolyzed cellulose.
While inhibition of cellulases by cellobiose has been extensively studied, cellobionic acid inhibition of cellulases has not received much attention. Since our system converts cellulose to cellobionic acid, it became evermore important to understand the inhibitory effects of cellobionic acid on cellulases. To better understand the inhibition effects of cellobionate, we investigated the inhibition of Trichoderma reesei CBHI, one of the most extensively studied CBHs, and the N. crassa CDH. The well-studied cellobiose inhibitor was characterized in parallel for comparison. Our data show that the oxidation of cellobiose to cellobionate has significant potential to improve cellulose conversion rates through inhibition relief.
Coffee and cookies will be served.
