New Test Corners Elusive Biofuels Enzyme

In a wood near you, powerful microbes quicken the decay of fallen tree branches. These adroit decomposers perform that essential role by producing specialized enzymes. In the United States and abroad, biofuels researchers prize these enzymes because they may speed and simplify the process of making bioethanol, and coproducts, from the cellulose in the cell walls of energy crops such as switchgrass.

One of the most sought-after of those specialty enzymes may now be easier for today's researchers to find. That's thanks to an assay created by Agricultural Research Service (ARS) chemist Charles C. Lee and colleagues at the agency's Western Regional Research Center in Albany, Calif.

High-speed and high-tech, but surprisingly affordable, the sophisticated assay equips scientists with a faster, less expensive way to discover genes that enable microbes to make an enzyme known as an alpha-glucuronidase. In nature, this enzyme cleaves glucuronic acid from hemicellulose and, in so doing, helps disassemble plant cell walls. Hemicellulose, cellulose and lignin are bound in a tight, complicated matrix that impedes other enzymes' ready access to the cellulosic sugars that are ideal for fermenting into bioethanol.

Right now, there are very few genes in the publicly available GenBank database that code for alpha-glucuronidases. The new assay, however, may change that by making it possible for scientists to quickly screen the genes in masses of anonymous microbes taken from the forest floor, compost heaps, or other outdoor places where decomposers live and work.

In brief, the test involves moving the DNA from the outdoor microbes into laboratory bacteria that, in petri dishes, will form telltale dark spots if they have alpha-glucuronidase genes and enzymes actively working inside. Scientists can then isolate and copy the genes from those bacteria, and perhaps re-tool the genes to make them even stronger and faster-acting, for tomorrow's biorefineries.

Lee developed the assay with Albany colleague Kurt Wagschal, patterning it upon an assay Wagschal built earlier for finding another in-demand biofuels enzyme. Lee also worked with Dominic W.S. Wong, George Robertson, William Orts, and Rena Kibblewhite. All are with the Bioproduct Chemistry and Engineering Research Unit at Albany.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.