Bt protein; also Bt toxin

A protein that is toxic to chewing insects and is produced by the soil bacterium Bacillus thuringiensis and has long been used as a biological pesticide.

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.

For genetically engineered insect resistance, different variants of Bt genes are transferred, e.g. Cry1Ab, Cry1Ac and Cry9c for maize. They differ both in terms of their length and in terms of the promoters used. The transgenic maize varieties differ depending on the Bt gene variant used, both in terms of the amount of Bt protein they produce and its distribution within the plant. Some Bt maize varieties produce the Bt protein primarily in the stem, while other produce it in all plant parts.