How does Bacillus Thuringiensis kill insects?

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Discovered in 1911, the bacterium Bacillus thuringiensis has been widely used as an insecticide since the 1950s; today it is the leading biological pest control agent for crop pests, particularly the caterpillars of Lepidoptera.

In addition, transgenic plants with the toxin gene of this bacterium are the most planted among genetically modified plants.

Although this bacterium and the toxin it produces have been studied for many years, the mechanism of action remains poorly understood. The commonly accepted assumption is that the toxin perforates the intestinal cells of the insect , leading to the lysis of these cells, and the death of the insect that stops feeding, or that in some cases death may be caused by a generalized infection by the bacteria.

BT Cotton plant

A new study to be published shortly in the  Proceedings of the National Academy of Sciences, led by Prof. Handelsman of the Department of Plant Pathology at the University of Wisconsin in Madison, shows that  Bacillus thuringiensis needs microorganisms from the intestinal flora of the insect to be lethal . The destruction of the native intestinal flora of the caterpillars with antibioticscancels out the lethal effects of Bt. However, the exact role played by the micro-organisms remains to be discovered.

The direct application of these results would be an optimization of the insecticidal effect of Bt by playing on microorganisms. In the longer term, understanding the mechanism of mediation between toxin and host microorganisms may have medical implications if found in some types of human infections.

Dr. Kimberly Seltzer

Postdoctoral Scholar, UC Berkeley Research Assistant, MIT

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