Bt toxin: inactive in the bacterium, active in the insect gut
"Bt toxin: inactive in the bacterium, active in the insect gut" is a free, interactive Class 12 Biology simulation for NEET, built on the lesson "Bt cotton" in Biotechnology and its Applications. Bacillus thuringiensis packs its insecticidal protein into crystals. Switch between the bacterium and a bollworm's midgut, and drag the slider through the stages. Bt toxin is an inactive protoxin crystal; the insect's alkaline gut activates it; the toxin binds midgut epithelial cells, makes pores, and the cells swell and lyse. cryIAc and cryIIAb proteins control cotton bollworms.
From the lesson Bt cotton in Biotechnology and its Applications. Change the values and watch what happens.
The idea behind it
NCERT §10.1
- Bt toxin is made by the bacterium Bacillus thuringiensis (Bt). Its gene has been cloned and expressed in plants, giving insect resistance without insecticides: in effect, a bio-pesticide.
- Crops given Bt genes include cotton and corn, and also rice, tomato, potato and soyabean.
- Some strains of B. thuringiensis make proteins lethal to particular insects: lepidopterans such as the tobacco budworm and armyworm, coleopterans (beetles), and dipterans (flies and mosquitoes).
- During one phase of growth the bacterium forms protein crystals that contain a toxic insecticidal protein.
- The toxin does not kill the Bacillus because it is stored as an inactive protoxin.
- In an insect that eats it, the alkaline pH of the gut solubilises the crystals and converts the protoxin into the active toxin.
- The active toxin binds to the surface of the midgut epithelial cells and creates pores, so the cells swell and lyse and the insect dies.
- Most Bt toxins act on one insect group, so the gene chosen depends on the crop and its pest. The toxin genes are named cry.
- Proteins coded by cryIAc and cryIIAb control cotton bollworms; the protein of cryIAb controls the corn borer.
Questions
2 answers
- What does the "Bt toxin: inactive in the bacterium, active in the insect gut" simulation show?
- Bacillus thuringiensis packs its insecticidal protein into crystals. Switch between the bacterium and a bollworm's midgut, and drag the slider through the stages.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Bt cotton" in Biotechnology and its Applications (Class 12 Biology).
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