Bt toxin

A protein toxic to insect pests, produced by the soil bacterium Bacillus thuringiensis

By means of genetic engineering, the genes for Bt toxin can be isolated from Bacillus thuringiensis and transferred to plants. The plant is thus conferred the ability to produce the insect toxin on its own.

There are different forms of Bt toxin that are specifically active against certain groups of insects. About 170 naturally occuring Bt toxins with varying specificities are known. 

Various versions of Bt genes are used in plant genetic engineering, e.g. Cry 1Ab, Cry1 Ac, and Cry 9c, to acheive insect resistance. They may also be combined with different promotors that specify the site-specificity and quantity of Bt toxin produced. Some Bt maize varieties produce Bt toxin mainly inside the stalk, some mostly in the roots, while others express it in all parts of the plant.