Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/3/2002
Publication Date: N/A
Citation: Interpretive Summary: Nematodes are microscopic roundworms that include beneficial species as well as parasites of plants and animals. The parasites cause billions of dollars of damage to crops and livestock in the United States each year. The serious problem farmers have in controlling nematodes is worsening because the most common pesticide used against plant parasites will soon be eliminated and because animal-parasitic nematodes are developing resistance against a common drug used to control them. In this paper, ARS scientists and collaborators explore new methods for controlling nematodes by examining the nematode-killing properties of naturally occurring toxins found in a safe, common bacterium called Bacillus thuringiensis. Seven toxins were evaluated in laboratory tests against one animal-parasitic nematode and five soil-dwelling, bacteria-feeding nematodes. The major findings were that four toxins damaged the guts of at least two nematode species and that each of the six species was damaged by at least one toxin. Because these particular toxins are not very damaging to insects, this study is significant because it is the first report on where in the body and how well these different nematode-specific toxins damage different nematodes, and it is the first report that shows that some can hurt an animal parasite. This information will be used by researchers to predict the best toxin to use against plant-parasitic nematodes and could eventually lead to safe and effective controls of nematode infections of plants and animals.
Technical Abstract: Bacillus thuringiensis crystal proteins are pore-forming toxins used around the world to control insects that attack crops and carry human disease. The extent to which crystal proteins might also target a different but important invertebrate phylum, nematodes, has until recently been largely ignored. Here, we produce seven crystal toxin proteins from two phylogenetically related subfamilies that might be predicted to target nematodes, and we assay their ability to target five diverse free-living nematode species. Using different assays, we demonstrate that four of these crystal proteins are toxic to at least two nematode species and that all nematode species tested are adversely affected by at least one toxin. Toxicity in nematodes correlates with damage to the intestine, consistent with the mechanism of action in insects. Unlike insects, the sensitivity of nematodes to different Bt toxins did not correlate with their phylogenetic relationships. One of the nematicidal crystal proteins is unrelated to the main family of crystal proteins, and its structure is unknown. We took advantage of our Bt - C. elegans system to efficiently delineate the active domain of this novel toxin. We demonstrate that Bt crystal proteins can target an animal parasite, indicating these proteins hold promise in controlling animal parasitic nematodes.