Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Most widely used organic pesticide requires help to kill

26.09.2006
The world's most widely used organic insecticide, a plucky bacterium known as Bacillus thuringiensis or Bt for short, requires the assistance of other microbes to perform its insect-slaying work, a new study has found.

Writing in the Sept. 26 issue of the Proceedings of the National Academy of Sciences (PNAS), a team of researchers from the University of Wisconsin-Madison reports that without the help of the native bacteria that colonize the insect gut, Bt is unable to perform its lethal work.

The startling new insight into the workings of one of the most important and environmentally friendly weapons in the human arsenal against insect pests has significant implications not only for the control of insects in agriculture, forestry and human health, but for understanding microbial disease in humans and other animals.

"The take-home message is that we've shown that the mechanism of killing for Bacillus thuringiensis is facilitated by the normal gut community," says Nichole Broderick, a UW-Madison graduate student and the lead author of the PNAS study. "This is a mechanism that was not previously known."

First discovered in 1911, Bacillus thuringiensis was developed as a commercially important insecticide in the 1950s. It is by far the most widely used natural agent to control important insect pests, and the genes that make Bt's toxic proteins have been engineered into numerous crop plants. Transgenic crops using the bacterium's genes are the most prevalent of any engineered plants, and are planted on millions of acres in the United States alone.

Although Bt and the toxic proteins it makes have been studied for decades, how the microbe goes about killing the insects it infects has been assumed to be a simple toxin-mediated disruption of the cells that line the insect gut. The damaged cells, according to the prevailing hypothesis, lead to starvation. An alternative hypothesis holds that the spread of the bacterium in infected insects leads to blood poisoning and death.

"It was one of those assumptions built on assumptions -- a scientific house of cards," explains one of the report's authors, Jo Handelsman, of the long-held view of Bt's mode of killing. "What was proposed as a hypothesis in one paper became cited as proven in another and no one seemed to go back to the original literature until now."

Handelsman is a Howard Hughes Medical Institute Professor in the UW-Madison department of plant pathology.

The new work, conducted in the laboratories of Handelsman and Kenneth F. Raffa, a professor in the UW-Madison department of entomology, demonstrates that Bt requires the presence of other bacteria to exert its lethal influence.

Virtually all animals, including humans, depend on the interplay of numerous species of bacteria that, beginning at birth, routinely colonize the stomach and intestines. The caterpillars of moths and butterflies, for example, have anywhere from seven to twenty species of gut bacteria. Humans have between five hundred and one thousand species of micro flora that take up residence in the intestinal tract.

"In moths and butterflies, the complexity is much lower than in mammals, and even some other insects," Broderick explains.

The Wisconsin study was conducted using antibiotics to clear all of the native bacteria that colonize the gut of gypsy moth caterpillars. Exposed to Bt, the caterpillars whose intestinal tracts had been cleared of their native microbial communities showed none of the agent's toxic effects.

When the insect's microbial gut flora were reestablished, Bt's insecticidal activity was restored. To further test their results, the Wisconsin team used a strain of live E. coli engineered to carry the Bt toxin to infect caterpillars, a lethal treatment whether or not the insect gut contained its normal complement of microbes. However, if the engineered E. coli was killed before administration, it only killed those caterpillars whose microbial gut flora were intact.

"The significance of the microbial community has been overlooked," Broderick asserts. "Ultimately, this is a toxin-mediated septicemia (blood poisoning) modulated by the gut community."

The exact role played by the microbes to promote the Bt toxin's lethal effects remains unknown.

The upshot of the new work may have immediate application in designing strategies to manage insect pests by enhancing the killing effects of BT using indigenous insect gut microbes or other bacteria known to promote blood poisoning.

"The work also raises the possibility that the genes encoding the (Bt) toxins could be deployed more effectively in transgenic crops by exploiting the role of insect-borne bacteria that enhance insecticidal activity," the Wisconsin team writes in its PNAS report.

What's more, the insight that gut microbes mediate the effects of bacterial toxins could have application in human and animal medicine as the roles of those bacteria become better understood. Bacterial infections in humans may account for as much as 10 percent of mortality in the United States.

"It is thought that the gut is the source of bacteria for a large portion of cases of human septicemia, so if this mechanism is shared by Bt and toxins produced by human pathogens, the implications could be far greater in medicine than in agriculture," Handelsman says.

Nichole Broderick | EurekAlert!
Further information:
http://www.entomology.wisc.edu

More articles from Agricultural and Forestry Science:

nachricht Climate change, population growth may lead to open ocean aquaculture
05.10.2017 | Oregon State University

nachricht New machine evaluates soybean at harvest for quality
04.10.2017 | University of Illinois College of Agricultural, Consumer and Environmental Sciences

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>