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Madelon Wise
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E-mail: mwise@fs.fed.us

TRANSLATION OF BROWN-ROT GENETIC CODE OFFERS PROMISE TO BIOFUELS INDUSTRY

MADISON, Wis.— An international team led by scientists from the U.S. Department of Agriculture Forest Service, Forest Products Laboratory (FPL) and U.S. Department of Energy (DOE) Joint Genome Institute (JGI) have translated the genetic code that explains the complex biochemical machinery making brown-rot fungi uniquely destructive to wood. The mechanisms by which these fungi gain access to energy-rich sugar molecules in wood may ultimately lead to innovations for the biofuels industry. The research, conducted by more than 50 authors, is reported in the February 4 edition of the Proceedings of the National Academy of Sciences (PNAS).

The paper describes analysis of the Postia placenta genome and reports a milestone in understanding lignocellulose conversions, a topic of considerable importance to the U.S. Departments of Agriculture (USDA) and Energy (DOE). Postia is representative of the 'brown-rot' fungi, which are common inhabitants of forest ecosystems and also responsible for the destructive decay of wooden structures. The costs of replacing decayed wood and the diminishing number of environmentally friendly preservatives have spurred FPL research on brown-rot fungi for decades.

In addition to their economic importance, the degradative capacity of wood decay fungi has attracted considerable research attention. Much of this research has focused on the degradation of lignin, the 'glue' that makes plant cells strong. Lignin is particularly stubborn to convert, but its removal is central to pulp and paper manufacturing. An earlier partnership between FPL, the DOE and the University of Wisconsin lead to genome completion of another wood decay fungus. Published in June 2004 in Nature Biotechnology, the lignin-degrading 'white-rot' fungus provided fundamental insight into the degradation of lignin.

In the past 5 years, DOE emphasis has shifted substantially to biofuels. Solid biomass --plants and trees-- can be converted into liquid fuels such as ethanol, methanol, and biodiesel. The challenge, however, lies in efficient conversion -- creating more energy than the input required to produce it.

A particular concern to the Forest Service is that our national forests are crowded with small-diameter trees, which negatively affect the health of the forests while increasing the threat of forest fires. Therefore, the Forest Service is critically concerned with finding good use for this material. The biggest challenge to producing ethanol from woody plant matter is in learning how to cost-effectively break down lignin and to convert cellulose to small, molecular-weight compounds that can be fermented into alcohol -- a crucial part of the biofuels process. Addressing this challenge, analysis of Postia has revealed a unique mechanism for deconstructing cellulose.

Microbiologist Dan Cullen, a principal investigator and one of three FPL scientists who worked on this study said, "The first step in this study was to elucidate the mechanism Postia uses to degrade cellulose." The team of scientists learned that Postia has unique attributes and a strategy for efficiently depolymerizing cellulose distinct from all known microbes, including the white-rot fungus previously studied.

"Nature offers some guidance here," said Cullen. "Postia has, over its evolution, shed the conventional enzymatic machinery for attacking plant material. Instead, the evidence suggests that it utilizes an arsenal of small oxidizing agents that blast through plant cell walls to depolymerize the cellulose. This biological process opens a door to more effective, less-energy intensive and more environmentally sound strategies for lignocellulose deconstruction."

Rapid break-down of cellulose is a distinguishing feature of brown-rot, and our systematic examination of Postia revealed unique extracellular enzyme systems." The genome information, Cullen says, "provides a framework for further investigations and a deeper understanding of biological processes involved in converting cellulosic biomass."

Although FPL Director Chris Risbrudt stresses that the mechanisms discovered in this study are "a long way from commercialization," these findings may add an important piece to solving the puzzle of cost-effective production of biofuels from forest biomass. Risbrudt adds that this study provides a side benefit to FPL and the public, "Analysis of the Postia genome also offers unparalleled opportunities for the development of more effective and environmentally-preferable wood preservation techniques."

The USDA Forest Service Forest Products Laboratory was established in 1910 in Madison, Wis., with the mission to conserve and extend the country's wood resources. Today, FPL's research scientists work with academic and industrial researchers and other government agencies in exploring ways to promote healthy forests and clean water, and improve papermaking and recycling processes. Information is available at FPL's Web site: www.fpl.fs.fed.us. Through FPL's Advanced Housing Research Center, (www.fpl.fs.fed.us/ahrc/), researchers also work to improve homebuilding technologies and materials.

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