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New Bacterium May Aid War on Insect Pests
Description: Scientists have discovered a bacterium with the same
insect-thwarting properties as the widely-used Bacillus thurengensis.
The bacterium, Photorhabdus luminescens, contains a toxin proven
effective against a broad array of insects, and promises to become a
potent, safe and environmentally benign weapon in the war against
insect pests.
EMBARGOED FOR RELEASE DEC. 17, 1997 CONTACTS: Jerald Ensign, (608)
262-7877; Richard ffrench-Constant, (608) 263-7924; David Bowen (608)
265-2470 (Editor's note: We've put together a news media resource
page at
http://www.w
isc.edu/news/news_images/bacteria.html for reporters who are
interested in viewing images as they prepare stories or organizations
wishing to download for publication.)
MOVE OVER BACILLUS THURENGENSIS BACTERIUM'S NEW-FOUND INSECTICIDAL
PROPERTIES RIVAL BT NASHVILLE - In the world of biological pest
control, Bacillus thurengensis, Bt for short, is the king of
insecticides. For 30 years Bt, a bacterium with remarkable
insecticidal properties, has been a pest-control mainstay for
foresters, farmers, gardeners and homeowners in search of a safe,
natural way to neutralize the bugs that bug them. As a form of
biological pest control, it is the only bacterium from which
widespread commercial applications have been possible, giving it, in
effect, a microbial monopoly on insect control worth hundreds of
millions of dollars. But now a team of scientists from two
laboratories at the University of Wisconsin-Madison, working in
collaboration with scientists from DowElanco of Indianapolis, hopes
to unleash a new bacterium with similar insect-thwarting
properties.
The bacterium, Photorhabdus luminescens, contains a toxin that has
proven effective against a broad array of insect pests - from
cockroaches to boll weevils - and promises to become a potent, safe
and environmentally benign weapon in the war against insect pests.
"It's a voracious pathogen. One bacterial cell can kill an insect,"
says Jerald Ensign, a UW-Madison professor of bacteriology who, with
then-graduate student David Bowen, discovered and characterized the
toxic potential of Photorhabdus, a widely-dispersed, multiple strain
bacterium that lives inside of and in symbiosis with soil-dwelling
roundworms called nematodes. The bacteria live inside the gut of
nematodes that invade insects.
Once inside an insect host, the bacteria are released from the
nematode, kill the insect, and set up rounds of bacterial and
nematode reproduction that turns the insect into a "protein soup,"
food for large numbers of nematodes. "This makes Alien look like a
cakewalk," says Richard ffrench-Constant, a UW-Madison professor of
toxicology in the department entomology. The Photorhabdus bacteria,
in fact, do Alien one better: The corpses left behind by the bacteria
glow in the dark as the microbe produces luminescent proteins in
addition to potent insecticides.
The findings of the Wisconsin group were reported here today (Dec.
17) at the annual meeting of the Entomological Society of America.
After establishing that Photorhabdus luminescens was indeed an
effective killer of a wide variety of insects, Bowen moved as a
post-doctoral fellow to the lab of ffrench-Constant where he
continued work on the biochemistry of the toxin and orchestrated a
nationwide survey for new toxic strains of the bacterium. So far,
that survey has yielded scores of new Photorhabdus
strains.
The discovery of a diverse new family of insect-killing bacteria
has added importance since, in recent years, some insects have
already begun to exhibit resistance to the Bt toxin, raising fears
that the biological pesticide may be losing its potency. By adding an
entire family of lethal bacteria to the biological pest-control
arsenal, the Wisconsin and DowElanco scientists have opened a
potentially broad new front in the war on insect pests since each of
the Photorhabdus strains produces its own variation on the toxin.
"What we have is a natural source, almost an infinite variety" of
toxic molecules, says ffrench-Constant. "We can't afford to hook
ourselves to a single bacterium or a single toxin." The Photorhabdus
toxin and the genes that produce it have been patented jointly by the
Wisconsin and DowElanco scientists through the Wisconsin Alumni
Research Foundation (WARF).
The technology has been licensed to DowElanco. In concentrated
doses, the toxin can be used as a spray or fed directly to insects.
The greatest potential application, however, lies in transferring the
toxin-producing genes from the bacteria to crop plants. Already,
scientists have transferred the genes that code for Bt's
insect-thwarting properties to important crop plants. Next year, an
estimated 3 million to 5 million acres of Bt transgenic corn will be
planted in the Midwest alone. "This deployment of Bt transgenic crops
is perhaps the biggest artificial experiment on natural selection in
insect populations since the introduction of synthetic insecticides
half a century ago," according to ffrench-Constant. The incentive to
confer crop plants with their own insecticides is huge. Farmers now
spend more than $575 million annually on chemical pesticides to
protect just one crop: corn. Bowen, working with colleagues Thomas
Rocheleau and Michael Blackburn in ffrench-Constant's lab, has
identified, cloned and sequenced the genes responsible for the
Photorhabdus' toxin.
Clones were independently derived at DowElanco as well. The next
step, already well underway, is to move those genes to any amenable
crop plant. Bringing a product to the field, however, may still take
anywhere from three to five years, says ffrench-Constant. "The need
for Bt replacements is critical before we have many crops in North
America expressing a limited range of Bt toxins," says
ffrench-Constant. "If we don't have them, it's an open invitation for
natural selection to confer resistance on insects and we'll lose that
control."
### - Terry Devitt, (608) 262-8282; trdevitt@facstaff.wisc.edu