A joint effort by several research laboratories is working to make biofuels a viable and sustainable energy resource.

As greenhouse gas emissions grow and world oil fields potentially pass their peak production, the search is on for future fuels that literally grow on trees. The U.S. Department of Energy (DOE) has established three Bioenergy Research Centers that will lay the foundation for a plant-based energy economy. Consisting of uniquely structured partnerships among National Laboratories, universities, nonprofit research centers and private companies, each center is receiving $25 million in annual federal funding. The plan is to provide each with up to $135 million through 2012. Results of fundamental research performed by the centers will provide the nascent bioenergy industry with the critical new techniques and tools needed to make production of cellulosic biofuels (biofuels made from nonfood plant fiber) efficient, economical and sustainable.

Although the three centers share the common goal of achieving new breakthroughs in the transformation of plant matter into biofuels, each center has a unique perspective and approaches the problem from a variety of different angles. “We are bringing to the table different approaches and ways of thinking that increase our chances of success,” said Tim Donohue, director of DOE’s Great Lakes Bioenergy Research Center (GLBRC) in Madison, Wisconsin, and a professor of bacteriology at the University of Wisconsin-Madison. “It increases the probability that society is going to reap the benefit of this investment by putting their eggs in several baskets.”

The centers have their work cut out for them. At present, converting plants into fuels is a costly, multistep process that must be made cheaper and more efficient before it can compete with fossil fuels in the marketplace. “We are focusing on the major problem of why biofuels are not a sustainable industry,” commented Martin Keller, director of the DOE’s BioEnergy Science Center (BESC) based at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee.

The structures of plants themselves pose the first hurdle. Plant cells are built of interwoven large polymeric molecules. The breakdown of these molecules leads to sugars that microbes can ferment into fuels such as ethanol. These polymeric molecules are very sturdy and resist both chemical and mechanical breakdown, necessary to get access to the sugars.To overcome this problem, called recalcitrance, BESC researchers are working to identify the thousands of genes involved in plant cell wall construction and how they interact to build stems, trunks and leaves. “Once we know the genes, we can start examining how we can change them to make the plant easier to digest,” said Keller. That includes the automation of the screening of plant samples for desirable traits with methods commonly found in the pharmaceutical industry, which routinely tests vast libraries of chemical compounds for potential drugs.

But sugars aren’t the only viable source of plant energy. Plants also store their biochemical energy in energy-rich molecules such as oils and starches. GLBRC is studying how to maximize the oil and starch yield in leaves and other nonedible portions of plants. “If we could breed plants to accumulate as much as 20 percent oils, we could double the energy produced per acre of land,” Donohue said.

An area that bioenergy scientists are working to streamline is the laborious process required to refine green plants into biofuels. At present, breakdown enzymes produced by one set of microbes must be grown and purified before being added to harvested plants. A second set of microbes is then used to ferment the plant sugars into biofuels such as ethanol. BESC aims to collapse these three steps into one with a single organism that can both manufacture catalyst enzymes and ferment the sugars into biofuels. “This type of consolidated bioprocessing provides the biggest savings and could completely change the economics of biofuels,” Keller said. His researchers have already identified one such multitalented microbe and are using a combination of genetic and genomic tools to optimize its performance.

To further speed the breakdown of raw plant biomass process, scientists at the DOE’s Joint Bioenergy Institute (JBEI) in Emeryville, California, are studying how to pretreat plants with ionic liquids before they are added to fermenters. Ionic liquids are made of ions similar to table salt, but are liquid rather than solid at room temperature. Early results show that ionic liquid pretreatment can break down plant cell walls more rapidly and effectively than current treatments using acid or ammonia. Ionic liquids also do not cause downstream problems, such as inhibition of microbial fermentation, which can decrease the efficiency of biofuel synthesis.

At the same time, JBEI scientists are building a better biofuels manufacturing microbe from scratch. “We view all these enzymes and metabolic pathways as parts. We want to put them onto the chassis of a microbe and modify the parts to get the greatest benefits from them,” said JBEI scientist Blake Simmons. Leading their efforts is synthetic biology pioneer and JBEI director Jay Keasling, who is also a professor of bioengineering and chemical engineering at the University of California-Berkeley, and the director of the Physical Biosciences Division at Lawrence Berkeley National Laboratory (Berkeley Lab) in Berkeley, California.

While current biofuels are made of food crops, such as corn and sugar cane, scientists working at the Bioenergy Research Centers envision a far more diverse portfolio of bioenergy crops. The centers are examining a wide range of fast-growing perennial plants that are already found in abundance in different regions of the country. Switchgrass might be the preferred biofuels crop in Nebraska and Florida, refineries in Hawaii might use eucalyptus while those in Pennsylvania might use silver maple. Excess biomass produced by forests and farms also could contribute. “It’s not so much a silver bullet that we need but a silver shotgun,” remarked Berkeley Lab scientist Blake Simmons. “We’ll have tens if not hundreds of solutions that make the most of our diverse geographical climate, growing conditions and water availability.”

Biofuel crops will have an impact on soil fertility, water and air quality, animal migration patterns and land use, as well as local and global economies. To that end, GLBRC scientists are developing tools with economists, engineers and others to maximize the environmental benefits of a biofuels economy. “We want to enter this new world with our eyes open,” Donohue said. Researchers at Berkeley Lab are looking even further ahead by developing third-generation biofuels that are chemically equivalent to gasoline, diesel or jet fuel.

Other experts say the DOE Bioenergy Research Centers will play a critical role in jump-starting the nascent biofuels industry. “These government centers are working at a basic research level on questions of practical importance that private companies can pick up and move with,” said Doug Cameron, chief science advisor for Piper Jaffray, a global investment bank headquartered in Minneapolis, Minnesota, and a member of the GLBRC external advisory board. Although all private companies involved in alternative fuels need to understand the detailed physical composition of plants and how best to deconstruct their scaffolding, “almost none of them can afford to have people working on it at the level you have at these government-funded centers,” according to Cameron.