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 How much drought can a forest take?
20.01.2017 | University of California - Davis

nachricht Plasma-zapping process could yield trans fat-free soybean oil product
02.12.2016 | Purdue University

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: Quantum optical sensor for the first time tested in space – with a laser system from Berlin

For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.

According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Tracking movement of immune cells identifies key first steps in inflammatory arthritis

23.01.2017 | Health and Medicine

Electrocatalysis can advance green transition

23.01.2017 | Physics and Astronomy

New technology for mass-production of complex molded composite components

23.01.2017 | Process Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>