DNA Sequencing Project Could Help in Biofuel Production

A Penn State genome-sequencing project involving an exotic insect pest recently was designated as a top priority by the U.S. Department of Energy's Joint Genome Institute. The project aims to sequence the genomes of microbes that live in the gut of the Asian longhorned beetle. The goal is to explore microbiological approaches to developing new sources of energy.

The Asian longhorned beetle is an invasive species that kills hardwood trees such as maple, box elder, horsechestnut, elm, and poplar. According to Kelli Hoover, associate professor of entomology, the insect was brought into the United States in wood pallets and other wood packing material accompanying cargo shipments from Asia. "They were first discovered in 1996 on several hardwood trees in Brooklyn, New York. The beetles quickly spread to Long Island, Queens, and Manhattan. Currently, quarantine and control strategies are in place in New York, Illinois, and New Jersey to help eradicate this serious pest."

Adults are easy to spot. "About one to 11/2 inches long, Asian longhorned beetles have long antennae and are shiny black with white markings," Hoover says. "After mating, adult females chew depressions into the bark of trees where they lay their eggs. Once the eggs hatch, small white larvae bore their way through the bark and into the tree. As they feed deeper into the tree's heartwood, they form tunnels, or galleries, in the trunk and branches. This damage weakens the integrity of the tree and will eventually kill it if the infestation is severe enough."

Hoover says that over the course of a year, a larva will mature and then pupate near the surface, under the bark. From the pupa, an adult beetle emerges, chewing its way out of the tree and forming characteristic round holes approximately 3/8 of an inch in diameter. "Many holes will appear on a heavily infested tree, usually accompanied by sawdust and sap oozing from the holes. The beetles emerge from June through October, with adults flying in search of mates and new egg-laying sites to complete their life cycle."

So how does this relate to alternative energy? According to Hoover, Asian longhorned beetles produce a diverse set of enzymes, which in combination are able to degrade woody biomass to simple sugars that may be useful in the production of biofuels, such as cellulosic ethanol. "In contrast to other wood-boring beetles, Asian longhorned beetles feed on healthy trees in addition to decaying trees," she explains. "They presumably contain lignin-degrading fungi internally, rather than ingesting the fungi present in decaying wood. The sequence information is likely to reveal a variety of enzymes in the beetles capable of degrading cellulose, hemicellulose, and lignin. In addition to biofuels, the enzymes might be used in bioremediation, textiles, and food production."

The Penn State team working on the project consists of a diverse group of scientists including Hoover, John Carlson, director of the Schatz Center for Tree Molecular Genetics, Ming Tien, professor of biochemistry, Maria Jimenez-Gasco, assistant professor of plant pathology, and Scott Geib, graduate student in entomology.

—Kristie Auman-Bauer