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Novel fungus helps beetles to digest hard wood
By Penn State,
Aug 18, 2008 - 3:59:37 AM
University Park, Pa. -- A little known fungus tucked away in the gut of Asian longhorned beetles helps the insect munch through the hardest of woods according to a team of entomologists and biochemists. Researchers say the discovery could lead to innovative methods of controlling the invasive pest, and potentially offer more efficient ways of breaking down plant biomass for generating biofuels.
Microbes in the gut of insects are known to break down cellulose, but little is known about how, or whether, insects degrade lignin. This natural polymer helps plants stay upright and protects them from most forms of microbial attack.
Lignin is nature's plastic and any organism that wants to get to the sugars in a plant has to be able to get past this protective barrier, said Ming Tien, study co-author and Penn State professor of biochemistry and molecular biology. We suspect that the fungus produces enzymes that help the beetles degrade lignin.
Before this report, it was thought that insects are unable to extensively break down lignin, and that they get around the problem either by feasting on wood that has already degraded, or by living close to fungi that can degrade the wood for them.
But this theory fails to explain the ability of insects to feed and grow within healthy living trees.
How these insects are able to circumvent this plastic wall [lignin] and get at the goodies, the sugars, behind it has remained a mystery, said Tien, who was recruited by Kelli Hoover, co-author and Penn State associate professor of entomology, and Scott Geib, lead author and Penn State doctoral student in entomology, to tease out an explanation.
The Asian longhorned beetle is one such insect that attacks healthy trees and bores through the hard wood to get at the succulent energy-rich matter inside. In the process, this invasive pest from China grows nearly 300-fold from being about the size of a grain of rice to a few inches in length.
Hoover and her colleagues speculated that the beetle could be harboring a community of microbes in the gut, which helps in breaking down lignin.
The researchers compared the chemical structure of non-degraded wood before and after it had passed through the gut of two wood-eating insects. To measure the degree of change in the lignin, they first fed pin oak wood to Asian longhorned beetles. Next they fed ponderosa pine wood to the Pacific dampwood termite, an insect that typically eats only dead wood.
Chemical analyses of feces from the two bugs indicated that they are able to alter the chemical structure of lignin by selectively adding or removing certain groups of molecules from the polymer.
Such alterations, said Geib, make it easier for the insect to break down wood.
This fungus has genes that then make enzymes, explained Hoover, whose team's findings appear today (Aug. 18) in the
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