The team cloned seven of Bt's nematode-specific crystal proteins
into E. coli bacteria and tested them against five bacteria-feeding
nematodes and one that parasitizes animals.
"Four toxins damaged the gut of at least two nematode species,"
says Carta. "Each of the six nematode species was damaged by at
least one toxin. This is the first report on the killing of nematodes
in general by Bt crystal toxins independent of Bt bacteria.
It shows how well these different toxins damage various nematodes."
Carta adds that it's also the first report of crystal toxins harming
an animal parasite. "This provides a foundation for future use
of these mammalian-safe toxins against plant-parasitic nematodes that
Dr. Aroian's laboratory is currently investigating," she says.
Focus on Sterols
Chitwood is studying ways to disrupt biochemical development pathways
in nematodes. He's focusing on the pathway for sterolschemical
compounds found in the cells of plants and animals. The most common
of these is cholesterol.
"Nematodes can't make their own cholesterol," says Chitwood.
"But they can use nonfunctional sterols found in their hosts and
convert them into cholesterol and other sterols for cellular function."
Previous studies in C. elegans found that blocking sterol conversion
to cholesterol through use of azacoprostane causes serious defects in
germ cell and cuticle development, growth, and motility. It also specifically
inhibits at least one enzyme involved in nematode sterol metabolism.
Azacoprostane is a chemical analog of cholesterol developed by ARS chemists
during the 1980s.
In a followup, Chitwood, along with researchers Byung-Kwon Choi and
Young-Ki Paik from Yonsei University in Seoul, South Korea, sought to
learn exactly how disruption of sterol metabolism actually kills nematodes.
They focused specifically on the effects of azacoprostane on nematodes'
synthesis of different kinds of proteins.
"The results indicated that treated nematodes contain low levels
of some important proteins usually abundant in their body walls and
other proteins involved in transporting fats within them," says
Chitwood. "They showed that nematode sterols regulate synthesis
of their proteins."
Chitwood says all these studies may lead to safe, innovative strategies
for managing this important crop pest. "We're turning the nematode's
own biology against itself," he says. "This can be put into
practical use by applying compounds to soil that re-create our results
or by engineering plants to produce antinematode compounds or genetically
based resistance."By Luis
Pons, Agricultural Research Service Information Staff.
This research is part of Plant Diseases (#303) and Methyl Bromide
Alternatives (#308), two ARS National Programs described on the World
Wide Web at www.nps.ars.usda.gov.
David J. Chitwood
is at the USDA-ARS Nematology
Laboratory, 10300 Baltimore Ave., Bldg. 011A, BARC-West, Beltsville,
MD 20705-2350; phone (301) 504-8634, fax (301) 504-5589.
"An Inside Job: Using Nematodes' Own Biology Against Them"
was published in the August
2004 issue of Agricultural Research magazine.