Put a Poplar in Your Tank
December 2006 / January 2007
Volume 4 Number 6
Wood from a common tree may one day become a renewable resource from which ethanol can be more efficiently and economically rendered to help meet U.S.
transportation fuel needs. Research on the fast-growing poplar tree, highlights the analysis of the first complete DNA sequence of a tree, the black cottonwood or Populus trichocarpa. The genome is the blueprint for the tree's biochemical pathways, including those responsible for constructing cellulose, a major component of plant cells. With the DNA code of the poplar now publicly available, the groundwork is in place for breeding strategies to improve trees as an ideal "feedstock" for a new generation of clean biofuels, such as ethanol derived from cellulose.
The research is the result of a four-year scientific and technical effort, led by the Department of Energy's Joint Genome Institute (DOE JGI) and Oak Ridge National Laboratory, which united the efforts of 34 institutions from around the world including the University of British Columbia, Genome Canada and Umeå Plant Science Centre of Sweden.
"Biofuels are not only attractive for their potential to cut reliance on oil imports but also their reduced environmental impact," said Dr. Gerald A. Tuskan, a DOE researcher and lead author of the study published in Science Magazine.
"Biofuels emit fewer pollutants than fossil fuels such as gasoline. In addition, poplar and related plants are vital managers of atmospheric carbon. Trees store captured carbon dioxide in their leaves, branches, stems and roots. This natural process provides opportunities to improve carbon removal from the air by producing trees that effectively shuttle and store more carbon below ground in their roots and the soil. Moreover, bioenergy crops re-absorb carbon dioxide emitted when biofuels are consumed, creating a cycle that is essentially carbon neutral."
Among the major discoveries yielded from sequencing the poplar is the identification of more than 90 genes associated with the production of cellulose, hemicellulose and lignin, the building blocks of plant cell walls.
The biopolymers cellulose and hemicellulose constitute the most abundant organic materials on earth. Through enzymatic action, they can be broken down into sugars that in turn can be fermented into alcohol and distilled to yield fuel-quality ethanol and other liquid fuels.
The poplar project supports a broader DOE drive to accelerate research into biofuels production, under the administration's Advanced Energy Initiative. In August, the department announced it would spend $250 million over five years to establish and operate two new Bioenergy Research Centers. The DOE-supported research into biofuels is focusing on both plants and microbes, in an effort to discover new biotechnology-based methods of producing fuels from plant matter (biomass) cost-effectively.
"There are many environmental benefits of an ethanol-based transportation fuels industry, and poplars have a significant role to play in the development of such an industry," said Brian Stanton, managing director of resource management for Greenwood Resources. Stanton has overseen the technological developments for poplar on commercial fiber farms where he has produced more than 40,000 hybrid varieties that have been tested throughout the United States, Chile, China and Europe. "Access to the genome information from poplar will enable us to more effectively sequester (capture) carbon, lower inputs of fertilizer and pesticides, reduce soil erosion, protect water and air quality, and improve the wildlife habitat within the context of a fully sustainable production system."
"The poplar genome project provides the foundation for the development of tree crops that will play an important role in the growth of cellulose as an important national and worldwide source of renewable fuels, chemicals and power," said Art Wiselogel of BBI International, a major service provider to the renewable fuels industry and a recognized leader in the ethanol industry.
Wiselogel's project development division has done more than 150 renewable fuels feasibility studies (including cellulosic ethanol), and has developed several ethanol plants in Kansas, Colorado and New York. "As the rapidly growing ethanol industry expands to include cellulosic technologies, the development of tools such as those that can be produced from the poplar genome project will be crucial to the production of tree crops to help fuel the nation and the world," Wiselogel said.
"Wood is a renewable resource that supplies the feedstock for our energy, building, communications and packaging needs," said Maud Hinchee, chief technology officer of ArborGen, a global leader in the research, development and commercialization of applications in genetic and new technology that will improve forest sustainability and productivity. "The sequencing of the Populus genome enables researchers to better understand how to grow trees for all applications including pulp and paper, wood products, and biofuels industry needs." Hinchee anticipates that wood products grown as a dedicated energy crop will contribute feedstock in support of the goal set by Secretary of Energy Samuel Bodman of replacing 30 percent of current transportation fuel demand with biofuels by 2030.
Earlier this year, DOE published a study summarizing the views of leading scientists in the field of biofuels research that expressed optimism about the prospects for finding cost-effective methods to produce fuels such as ethanol from cellulose in the not-too-distant future (Breaking the Biological Barriers to Cellulosic Ethanol, available at http://genomicsgtl.energy.gov/biofuels/b2bworkshop.shtml).
DOE scientists envision a future in which vast poplar farms in regions such as the Pacific Northwest, the upper Midwest, and portions of the southeastern United States could provide a steady supply of tree biomass rich in cellulose that can be transformed by specialized biorefineries into fuels like ethanol.
Other regions of the country might specialize in different "energy crops" suited to their particular climate and soil conditions, including such plants as switchgrass, also being sequenced by DOE JGI. In addition, a large quantity of biofuels might be produced from agricultural and forestry waste.
DOE JGI is also working on characterizing microbes isolated from environmental samples for their potential to produce enzymes that can ferment the sugars in plant material to a higher percentage of ethanol, and thus decrease energy and resources needed for distillation.
More information about DOE JGI, which unites the expertise of five DOE national laboratories—€”Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge and Pacific Northwest, along with the Stanford Human Genome Center—€”can be found at www.jgi.doe.gov.
David Gilbert is public affairs manager for the DOE Joint Genome Institute.
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