Progress 10/01/05 to 09/30/07
Outputs
OUTPUTS: Bacillus thuringiensis (Bt) is the most widely used microbial pesticide in agricultural and forest ecosystems. It offers a number of advantages over traditional synthetic insecticides, including a narrower range of susceptible species (typically at the level of insect orders), brief residual times in the environment, and extremely low toxicity to vertebrates. The gene encoding the Bt endotoxin is now the most commonly deployed transgene in crops, having achieved widespread utility in cotton, corn, and potatoes, among others. Synthetic pesticide inputs have decreased in systems where Bt application has risen. Despite these advantages, further substitution of synthetic insecticides with the more environmentally benign Bt faces a number of challenges. First, Bt often exhibits lower efficacy than synthetic insecticides. Bt also poses significant nontarget effects. Although preferable to the broad-spectrum organophosphates, carbamates, and pyrethroids, Bt is toxic to many (or
most) species within the order to which the target pest belongs. A third challenge to continued use of Bt involves biotype evolution. Insects commonly evolve resistance against any treatment, whether pesticides, cultural practices, or resistant varieties, that exert intense mortality and unidirectional selection pressures on their populations. Our goal is to identify compounds that synergize the insecticidal activity of Bacillus thuringiensis (Bt) against lepidopteran insects and determine the mechanism of synergy. In our previous work we identified a number of potent synergists, including the novel antibiotic, zwittermicin A, and synthetic phenolic glycosides, a group of compounds related to the phenolic glycosides found in aspen leaves, which are also known to be synergistic with Bt toxin. We have synthesized a variety of phenolic glycosides using a combinatorial approach that relies on inexpensive, microwave-driven chemistry. To identify features of the phenolic glycosides that are
essential for activity, we will conduct a structure-function analysis by testing a large collection of these synthetic compounds for synergistic activity. As we began exploring the mechanism of synergy, we found that the gut microbial community is required for Bt activity. This is surprising, new information about Bt because it has been studied for almost a century and was never shown to require other bacteria for mortality. Our next goal is to determine the role of the gut bacteria in Bt killing and determine whether there is an interaction with synergists. Our working hypothesis is that the gut bacteria, in concert with Bt, incite an inflammatory response, much like the cause of sepsis in mammals. We have found that proinflammatory compounds promote the activity of Bt whereas anti-inflammatory compounds reduce Bt killing.
PARTICIPANTS: Nichole Broderick Joey Strange Valent Biosciences, the largest producer of Bt in the world, meets with us quarterly and their scientists are interested in the research.
TARGET AUDIENCES: Scientific community, agricultural community, lay public Conducted interviews with two UW reporters.
Impacts
This work will contribute to our understanding of the interactions of plant chemistry, bacterial toxins, and insect gut communities and may lead to new strategies to enhance the activity of Bt toxin in agriculture and forestry.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
The goal of the project is to identify compounds that synergize the insecticidal activity of Bacillus thuringiensis (Bt) against lepidopteran insects. In our previous work we identified a number of potent synergists, including the novel antibiotic, zwittermicin A, and synthetic phenolic glycosides, a group of compounds related to the phenolic glycosides found in aspen leaves, which are also known to be synergistic with Bt toxin. In the proposed research, we using two approaches to find economically viable synergists. First, we are attempting to elucidate the biosynthetic pathway for zwittermicin A, which remains the most potent synergist in our arsenal. We have cloned the genes encoding the complex pathway, which appears to require more than 60 enzymes, and we have begun to delineate the biochemical function of each gene in the pathway. This work has identified some interesting features of the biosynthetic apparatus, including a regulatory system that may repress
production of zwittermicin. We are exploring the possibility that removing the repressor will enhance production of zwittermicin. We have also developed a combinatorial approach to synthesize a large collection of phenolic glycosides. We develop very inexpensive and rapid chemistry (referred to as 'click chemistry') to synthesize a variety of compounds with facility. Thus far, we have synthesized a number of compounds that are synergistic with Bt toxin, but none are as potent as zwittermicin A. To identify features of the phenolic glycosides that are essential for activity, we will conduct a structure-function analysis by testing each compound for synergy with Bt toxin in an assay for mortality of gypsy moth larvae. To understand the mechanism of synergy, we tested the hypothesis that synergistic activity is associated with changes in the microbial community of the insect gut. In pursuing this hypothesis, we made the most surprising discovery that Bt toxin does not kill insect larvae
directly, but simply facilitates septicemia induced by normal residents of the larval gut. Germ-free insects are not susceptible to Bt toxin, but when Enterobacter, a normal member of the gut microbiota, is added back to the germ-free animals, Bt induces insect death. Bt does not grow in the insect's hemolymph whereas Enterobacter does, making it a far better candidate to induce septic death than Bt, which has long been assumed to be the direct cause of mortality. This work opens up an entirely new area of research on Bt, which involves manipulating the gut microbiota to achieve more efficient killing by Bt.
Impacts
This work will lead to development of new pest control strategies. These may entail chemical synergists (such as zwittermicin A or phenolic glycosides) for Bt or microorganisms that are enabled by Bt to induce septic death.
Publications
- Chan, Y.A., Boyne, M.T., Podevels, A.M., Klimowicz, A.K., Handelsman, J., Kelleher, N.L., and Thomas, M.G. 2006. Two new polyketide synthase extender units: hydroxymalonyl-acyl carrier protein and aminomalonyl-acyl carrier protein. Proc. Natl. Acad. Sci. USA. 103(41):14349-14354.
- Broderick, N.A., Raffa, KR., and Handelsman, J. 2006. Midgut bacteria required for Bacillus thuringiensis insecticidal activity. Proc. Natl. Acad. Sci. USA. 103(41):15196-15199.
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Progress 01/01/05 to 12/31/05
Outputs
The goal of the project described here is to identify compounds that synergize the insecticidal activity of Bacillus thuringiensis (Bt) against lepidopteran insects. In our previous work we identified a number of potent synergists, including the novel antibiotic, zwittermicin A, and synthetic phenolic glycosides, a group of compounds related to the phenolic glycosides found in aspen leaves, which are also known to be synergistic with Bt toxin. In the proposed research, we will use a combinatorial approach to synthesize a large collection of phenolic glycosides. To identify features of the phenolic glycosides that are essential for activity, we will conduct a structure-function analysis by testing each compound for synergy with Bt toxin in an assay for mortality of gypsy moth larvae. Finally, to begin exploring the mechanism of synergy, we will test the hypothesis that synergistic activity is associated with changes in the microbial community of the insect gut. To test
this hypothesis, we will determine the effect of the compounds on the composition of the gut community. This work will contribute to our understanding of the interactions of plant chemistry, bacterial toxins, and insect gut communities and may lead to new strategies to enhance the activity of Bt toxin in agriculture and forestry.
Impacts
This work will contribute to our understanding of the interactions of plant chemistry, bacterial toxins, and insect gut communities and may lead to new strategies to enhance the activity of Bt toxin in agriculture and forestry.
Publications
- No publications reported this period
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