Glucose yields sweet pest control

The key to fighting the ravages of termites and other insect pests could lie in the ubiquitous glucose molecule, tweaked to weaken insect immune systems, say researchers from the Massachusetts Institute of Technology. Formosan subterranean termites Photo by Scott BauerThe scientists have shown that the glucose relative, D-δ-gluconolactone (GDL), can disrupt the activity of a termite protein crucial for sensing and killing invading microbes, making the pests susceptible to pathogenic bacter

Bob Grant

| 3 min read

Formosan subterranean termites
Photo by Scott Bauer

The scientists have shown that the glucose relative, D-δ-gluconolactone (GDL), can disrupt the activity of a termite protein crucial for sensing and killing invading microbes, making the pests susceptible to pathogenic bacteria or fungi that routinely buffet them, they linkurl:report;http://www.pnas.org/cgi/doi/10.1073/pnas.0904063106 in this week's issue of the __Proceedings of the National Academy of Sciences__. "When you have an immune system that is compromised, you have a variety of opportunistic infections that take over," linkurl:Ram Sasisekharan,;http://web.mit.edu/be/people/sasisekharan.htm an MIT bioengineer who led the study, told __The Scientist__. "You give these microbes sort of a leg up to attacking more seriously." With termites causing $30 billion worth of damage to manmade structures and crops every year, this is good news for our species and bad news for the voracious insects. GDL lacks the toxicity and environmental longevity of many currently used pesticides, said Sasisekharan. "Most of the current pesticide strategies essentially involve using toxic compounds that go after the nervous systems of insects." GDL, however, is non-toxic and biodegradable, the product of a simple and inexpensive chemical modification of an everyday glucose molecule. Gram-negative bacteria binding proteins (GNBPs) in insects normally search for carbohydrate molecules embedded on the surface of microbes. To Sasisekharan's surprise, GNBP-2, the protein variant the researchers studied in termites, had an additional role. It not only sniffs out pathogenic infection by scanning for carbohydrates, but also acts as an enzyme that degrades these molecules. "It was fascinating," Sasisekharan said: GNBP-2 "was not only a sensing tool but it was a method that [termites] use to kill the microbes." GDL works by attaching to a crucial pocket on GNBP-2 adjacent to parts of the protein that aid in breaking down microbial polysaccharides. With their defense system occupied, the termites were overtaken by fungal and bacterial invaders and died within approximately a week. Termites have GNBP-2 in their cell membranes, but they also secrete the protein into their nest walls to set up a perimeter fence of sorts to guard against microbial invasion, the researchers found. "It was a mechanism that went beyond pathogen sensing into sort of community sensing," Sasisekharan said, "It was fascinating that this protein was expressed not only in the insect, but that they had a mechanism of secreting them." Sasisekharan suggested that including GDL in building materials or agricultural products, such as fertilizers, could be a way to combat termite attacks. So far, though, cautioned Mississippi State University pathologist/entomologist linkurl:Terry Amburgey,;http://www.giles.msstate.edu/professors/staff.php?guid=tla6 who was not involved in the study, while the biological mechanism behind GDL might be interesting, its application in a pest control setting may be a long shot. "It's one of those interesting things," he told __The Scientist__. "In 20 to 30 years it may be more than interesting." Amburgey, who is also part owner of pest control company TermiSys, said that logistical difficulties might plague the real world application of GDL. There's no clear method for delivering the molecule to termites, and the biodegradability of GDL might also be its downfall. It's fine to incorporate GDL into building materials, Amburgey said, but termites don't tend to infest built structures for 10-15 years after installation. "How long are these things going to be available?" Amburgey asked. "I just think that this is fraught with potential problems." Sasisekharan's group also found that other insect pests, such as locusts and roaches, share a similar family of GNBP proteins that function in the same way -- meaning that GDL might be effective in disrupting their immune systems as well.
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[3rd September 1990]