Fuels from biomass
29 May 2001
Researchers at the University of Colorado at Boulder have developed a novel process involving the production of ethanol that could lead to a significant decrease in the cost of renewable fuel.
Associate Professor Kathleen Danna of the molecular, cellular and developmental biology department and her research team created a new technique they expect to produce large amounts of low-cost, highly effective enzymes vital for the conversion of plant cellulose into ethanol. Successfully producing large quantities of the enzymes could significantly lower costs for the processing of renewable fuels from plant biomass, said Danna.
Ethanol, also known as ethyl alcohol, is a clean-burning fuel that is used as a gasoline additive in some states like Colorado during the high-pollution months in winter, said Danna. In Brazil, ethanol has been used on an experimental basis to run fleets of cars with specially modified engines using fuel made up of 95 percent ethanol.
Although the ethanol currently used as a fuel additive in America is derived from cornstarch rather than cellulose via biomass conversion, cornstarch as a source of raw material would not be able to meet the demand if ethanol were to become a major transportation fuel, she said. While there is a competing use for cornstarch - food - the supply of plant biomass is so large it often has a 'negative cost' in that households, industry and government often must pay for its disposal, Danna said.
Cellulose is the principal structural material in the cell walls of all land plants. Cellulose - essentially, repeating chains of glucose - needs to be broken down into smaller segments in order to produce ethanol.
A class of enzymes known as cellulase, which are found in some species of fungi and bacteria, break chemical bonds between glucose sub-units that make up cellulose. Fermentation of the glucose completes the conversion of cellulose to ethanol, Danna said.
Because the organisms that synthesize such enzymes are difficult to grow in large quantities needed for industrial application, the researchers have taken genes from certain bacteria harbouring the enzymes and injected them into plants. The plants then express the genes as the cellulase enzymes in large quantities within the cell walls of plants, she said.
One bacterium that has been used by the CU-Boulder researchers, and which contains genes that code for cellulase enzymes, was originally discovered in the hot springs of Yellowstone National Park by researchers at the National Renewable Energy Laboratory in Golden, CO, said Danna.
Most recently, the researchers have transplanted a bacterial gene that codes for cellulase into a tiny weed species in the mustard family known as Arabidopsis thallana. Raised in closed chambers set at temperatures of roughly 77 degrees Fahrenheit for optimal growth, the plants manufacture significantly large quantities of the cellulase enzyme, which then is harvested from the plants.
A number of plants might be viable candidates to produce large amounts of cellulase enzymes in their leaves and stems, said Danna, including tobacco and corn.
The effort led by Danna has earned the project recognition from the Consortium for Plant Biotechnology Research, which recently awarded the CU-Boulder team a $40,000 fellowship that will help fund research by Danna and biology Research Associate Sylvia Fromherz. The money will fund a project aimed at developing a superior cellulase enzyme and is receiving matching funds from industry and the Colorado Commission on Higher Education grants program to CU-Boulder.
