A Novel Biochemical Platform for Fuels and Chemicals Production From Cellulosic Biomass: Metabolic Engineering and Fermentation Optimization for Improved Yield of Ethanol and Reactive IntermediatesEPA Grant Number: FP917465
Title: A Novel Biochemical Platform for Fuels and Chemicals Production From Cellulosic Biomass: Metabolic Engineering and Fermentation Optimization for Improved Yield of Ethanol and Reactive Intermediates
Investigators: Hildebrand, Amanda M
Institution: University of California - Davis
EPA Project Officer: Michaud, Jayne
Project Period: September 1, 2012 through August 31, 2015
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2012) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Bio-Environmental Engineering
The proposed biochemical platform for cellulosic ethanol production consolidates the three most expensive steps in the conventional platform in a single, biological step. Cellulolytic microorganism(s) that can secrete all the enzymes needed to hydrolyze cellulose and hemicellulose despite the presence of lignin can be modified to convert most of the carbohydrate contained in the cellulosic biomass to sugar aldonates. In a second step, the sugar aldonates are utilized as the carbon source to produce ethanol and other products. Although the viability of this process has been demonstrated, substantial gains in sugar aldonate and ethanol yields are possible through metabolic and genetic engineering. Fermentation modeling and optimization will provide a means to further improve the overall yield of the process.
A metabolic engineering strategy will be employed to improve the yield of the sugar aldonate intermediates from cellulose, as well as the subsequent conversion of the sugar aldonates to ethanol. By knocking out certain genes in the cellulolytic organism, the carbon contained in cellulose will be diverted to the production of sugar aldonates. The study can ensure that the sugar aldonates are preserved as a carbon source for ethanol production rather than being consumed by the organism by knocking out genes involved in aldonate utilization. Additionally, genetic engineering can be employed to improve the activity of key enzyme(s) involved in converting cellulose to sugar aldonates. These processes can be modeled and optimized through a factorial design of experiment. Initial experiments will be conducted on the shake flask scale, followed by evaluation in a 1.3 liter bioreactor. Similarly, in the subsequent fermentation of these sugar aldonates to ethanol, genes for competing pathways can be inactivated to direct carbon flow toward ethanol production.
Preliminary experiments have demonstrated that sugar aldonates can be produced from cellulose by genetically engineering a cellulolytic organism, and that those aldonates can be converted to ethanol. By knocking out genes for competing pathways, it is expected that the yields for each of these steps will improve. By enhancing the activity of key enzymes involved, the conversion of cellulose to sugar aldonates can be improved further. Factorial designs will aid in understanding the key factors involved from a processing perspective, and a model will provide a tool for further optimization.
Potential to Further Environmental/Human Health Protection
Burning fossil fuels produces carbon dioxide, which is a major contributor of global climate change. With the supply of fossil fuels approaching depletion, the imbalance of power for the small collection of national suppliers of fossil fuels will become ever more disproportionate. The rising global demand for energy will only intensify these issues, creating an urgent need to develop alternative energy sources. The proposed biological platform seeks to advance the field of cellulosic ethanol by improving the overall processing costs through consolidation of the costliest process steps, bringing the industry one step closer to making renewable, economical and environmentally friendly energy a reality.