Tracking the Cell Wall Breakthrough

Native grasses and fast-growing trees are the best candidates for energy crops in the United States, according to the leading researchers in the field. After initializing and then expanding the use of marginal or idle lands for switchgrass, poplar trees and other species, technological and scientific research is developing rapidly and aggressively to transform the biomass energy crops into ethanol. In this second installment of a three part series, EPM looks at genetic research aiming to mutate these plants into a ethanol producer's dream.
By Nicholas Zeman | October 26, 2006
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When it comes to breaking down biomass, would-be cellulose ethanol producers are not unlike construction workers hammering on a thick foundation with hand tools.

"The iron rods in a concrete wall are like the long fibers of cellulose, and the lignin is like the cement so it is very hard to remove the rod from the cement," says Bikram Gill, professor of plant pathology at Kansas State University (KSU). "It is very hard to remove cellulose from the lignin."

When Gill heard President George W. Bush's State of the Union addressor what's being called "the switchgrass speech"in January, he hoped his lifetime studies of wheat genetics might be applicable to grasses. "Because wheat is a grass, it turned out that our genetic work might apply to this kind of research," he says.

The basic challenge will be to manipulate the DNA of various cellulosic sources. Researchers have already identified 50 gene sequences involved in the synthesis of lignins, which are a part of the cell walls. Cellulose is easy to convert into ethanol but difficult to extract from lignin. "Our proposal is to locate the weak link and knock down each gene to see what happens to the cell wall," says Gill, who is not alone in his efforts to delve into biomass research.

The financial success of, and political support for, ethanol has researchers across the country taking a serious look at the field. For instance, Steve Kelley, professor and department head of Wood and Paper Sciences at North Carolina State University (NCSU) in Raleigh, says the school's research can be valuable for ethanol feedstock development, as well. "There is probably about a 15-year history of modifying the chemical composition of wood," Kelley says. "The biotechnology involved in this process could be a lot like turning genes up and down for making ethanol."

Gill wants to produce a genetic lesion in the plant itself so that the cell wall is more amenable to cellulose extraction. This is performed by a sort of vaccination when the plant is infected with a genetically modified virus. The virus has had the gene, which causes the lignin and cellulose to be tightly bound, inserted into its molecular sequence. "We [are trying to] understand where particular genes play key roles, and how we can manipulate certain genes to be able to use this material more easily for making ethanol," Gill says.

When the plant's immune defenses attack the virus, the native gene-binding lignin and cellulose are also under siege. This process weakens the cell wall, making it more amenable to cellulose extraction. "We have a system where we can knock out a gene in a living plant within two weeks," Gill says. "Then, we can harvest the leaf and see what happens. You can disarm the virus and then put in the gene you want to knock out in this virus. Our research is long term. We want to analyze the nearly 50 genes involved in laying down the cell wall and try to find some weak link or produce some mutation."

Just like crops are bred for disease resistance or baking bread, if the genetic factors involved in cell walls are known, then scientific breeding could lead to crops that are much better suited for conversion into ethanol.

Joint Research
In July, the U.S. DOE published a 200-page scientific "roadmap" listing the research efforts required for overcoming challenges of the large-scale production of cellulosic ethanol. Feedstock development was one of the challenges identified by the roadmap, and a grant program was developed to accelerate the production of biomass that can be used to make renewable fuels. Gill received one of those grants worth $700,000, while NCSU received another $300,000 grant. These awards were among nine grants that were part of the $9 million program administered by the DOE and the USDA. "To be a reliable renewable energy source, farmers and ranchers will need to grow biomass in large quantities," Ag Secretary Mike Johanns said in a news release announcing the grant initiative. "This joint research initiative will address our nation's need for alternative energy resources, and improve the efficiency with which biomass and plant feedstocks are used to produce renewable fuels such as ethanol."

The focus of the research plan is to use advances in biotechnology first developed in the Human Genome Project and the Genomics:GTL program. While NCSU is researching trees, KSU is focusing on grasses because those crops grow predominantly in the Great Plains states. "This is a partnership to promote renewable energy resources in the United States, and we [received] one of the (nine) grants," Gill says. "So we're very excited of course."

The feedstock development program at Oak Ridge National Laboratory (ORNL), in Oak Ridge, Tenn., which is funded by the DOE, estimates that 400 million acres of land classified as cropland in the United States are suitable for growing dedicated feedstocks. Perennial grasses and trees can often be economically grown on land that is not suitable for conventional crops, while providing the same protection from erosion recommended for agricultural set-aside or Conservation Reserve Program lands.

ORNL, which is funded by the DOE, has identified hybrid poplars, hybrid willows, silver maples and switchgrass as having the most potential for use as bioenergy feedstocks over a wide geographic range. But this is just the beginning of work that will take decades. "It depends on support, resources, people and discovery," says Gerald Tuskan of ORNL, who was among the scientists responsible for the first complete DNA sequencing of a treethe black cottonwood. "In a fully funded resource scenario, within five years we could see plots of domestic trees being evaluated," Tuskan says. "Within 15 years of continued research, we could see employment of large-scale energy farms using poplar."

The theory is to optimize cell-wall chemistry to perfect the ratio of lignin to cellulose, as well as yield per unit area of land. "Increased yield does more to decrease the cost than anything we can do to manipulate the plant material," Tuskan says. The Joint Genome Institute says this research "lays the groundwork that may lead to the development of trees as an ideal feedstock for a new generation of biofuels."

There is a complex pathway involved in integrating a presently nonexistent dedicated energy crop into the nation's agricultural production. "If we had an improved corn stover strain, poplar or pine, it will take you five years just to produce the seed needed," Kelley says. "There is a whole pathway involved into getting a new seed or line into practice, and it's longer for trees than it is for crops."

Despite the challenges, poplar's extraordinarily rapid growth, and its relatively compact genome size of 480 million nucleotide units40 times smaller than the genome of pineare among the many features that led researchers to target poplar as a model for biofuels production.

Revitalization
Researchers at NCSU say that trees can potentially be modified with a genome approach for traits to overcome virtually any major biomass conversion barrier to ethanol production. However, the plant traits suited to ethanol production are poorly understood.

Researchers and politicians believe it is going to take more than corn for the United States to produce enough ethanol to significantly contribute to energy needs and domestic security. That will mean growing switchgrass, campus, poplar and corn. "The rate of this research is increasing rapidly," Kelley says. "When you think of how important energy is to our societyfrom sources that you can't count onI think this is a very wise investment."

Fortunately, there is an existing infrastructure in place for the proliferation of the poplar as a dedicated energy crop. "What you have right now is nearly 80 paper mills that have shut down within the past five years," Kelley says. "At least half could be opened back upnot to make paper but to make ethanol. All of these sites have experience collecting wood commercially in a sustainable manner. The sites are equipped with wastewater treatment facilities, boilers, heat and power, and are also already permitted to operate. "They even have all of this steel in the ground for bleaching and pulping chemistry," Kelley says. "Now, you would have to renovate the pots and put in a still, and that's tens of millions in capitalbut it's not hundreds [of millions]."

Scientists say that the conversion of these sites into production test facilities for cellulosic ethanol made from dedicated energy crops like poplar trees is feasible within the next five to 20 years. "You use these [paper] plants as test facilities, and the only risk is going to be the capital," Kelley says.

Nicholas Zeman is an Ethanol Producer Magazine staff writer. Reach him at nzeman@bbibiofuels.com or (701) 746-8385.