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 Trees and climate change: Faster growth, lighter wood
14.08.2018 | Technische Universität München

nachricht Animals and fungi enhance the performance of forests
01.08.2018 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig

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: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

Im Focus: World record: Fastest 3-D tomographic images at BESSY II

The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.

Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

'Building up' stretchable electronics to be as multipurpose as your smartphone

14.08.2018 | Information Technology

During HIV infection, antibody can block B cells from fighting pathogens

14.08.2018 | Life Sciences

First study on physical properties of giant cancer cells may inform new treatments

14.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>